Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries
BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m2743 (Published 15 July 2020) Cite this as: BMJ 2020;370:m2743Linked Editorial
Lockdown-type measures look effective against covid-19
Read our latest coverage of the coronavirus pandemic
All rapid responses
Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles or when it is brought to our attention that a response spreads misinformation.
From March 2022, the word limit for rapid responses will be 600 words not including references and author details. We will no longer post responses that exceed this limit.
The word limit for letters selected from posted responses remains 300 words.
Dear Editor
It was a pleasure for us to read the article titled “Physical distancing
interventions and incidence of Corona virus disease 2019: Natural
experiment in 149 countries” by Islam et al. [1] in your esteemed
journal. It is a well-written article and quite a relevant one during the
current pandemic crisis. It is a topic of interest for us and we would like
to add a few points which we feel would enrich the article further in
regard to the global response to the COVID-19 pandemic.
As this study mainly intends to pinpoint the way to control the
pandemic spread, personal hygiene measures like hand washing, use of
face mask, gloves etc. along with the physical distancing methods
would seem to have a greater impact on curbing the viral transmission.
While physical distancing protects ourselves from the virus, hand
hygiene and the use of face masks, especially surgical or N95 masks,
both reduces the risk of infection and reduces the risk of infecting
others. [2]
Secondly, paying attention to children and adolescents during the
global public health emergency is of special social significance and
clinical value for preventing the occurrence of mental disorders and
adverse events. Humanistic care and psychological interventions for
children are therefore some of the most important components of the
response strategies for the COVID-19 pandemic [3].
Finally, social distancing interventions can be effective against
epidemics but are potentially detrimental for the economy. Businesses
that rely heavily on face-to-face communication or close physical
proximity when producing a product or providing a service are
particularly vulnerable. [4] School closings have sent more than half a
billion children home, according to UNESCO. They could end up missing
months of education and many depend on free school lunch programs.
[5] Physical distancing alone may not be an adequate long term
solution to the crisis, and it is imperative that social and political
leaders, in association with medical experts, come out with reasonable
and scientifically-sound measures and protocols, that safely balance
reducing risk of infection while propping up the national economy.
REFERENCES:
1. Islam N, Sharp SJ, Chowell G, Shabnam S, Kawachi I, Lacey B, et
al. Physical distancing interventions and incidence of corona
virus disease 2019: natural experiment in 149 countries. BMJ
2020;370:m2743.
2. Roser, M., Ritchie, H., Ortiz-Ospina, E. and Hasell, J. (2020) -
"Coronavirus Pandemic (COVID-19)". Retrieved from:
https://ourworldindata.org/coronavirus. Accessed : 1 st October
2020
3. Ye J. Pediatric Mental and Behavioral Health in the Period of
Quarantine and Social Distancing With COVID-19. JMIR Pediatr
Parent2020;3(2):e19867.
4. Koren M, Peto R. Business disruptions from social distancing.
PLoS One. 2020; 15(9): e0239113. doi:
10.1371/journal.pone.0239113
5. Cohen J, Kupferschmidt K. Countries test tactics in ‘war’
against COVID-19. Science 2020;367(6484):1287-1288. DOI:
10.1126/science.367.6484.1287
Competing interests: No competing interests
Dear Editor
It was a pleasure for us to read the article titled “Physical distancing
interventions and incidence of Corona virus disease 2019: Natural
experiment in 149 countries” by Islam et al. [1] in your esteemed
journal. It is a well-written article and quite a relevant one during the
current pandemic crisis. It is a topic of interest for us and we would like
to add a few points which we feel would enrich the article further in
regard to the global response to the COVID-19 pandemic.
As this study mainly intends to pinpoint the way to control the
pandemic spread, personal hygiene measures like hand washing, use of
face mask, gloves etc. along with the physical distancing methods
would seem to have a greater impact on curbing the viral transmission.
While physical distancing protects ourselves from the virus, hand
hygiene and the use of face masks, especially surgical or N95 masks,
both reduces the risk of infection and reduces the risk of infecting
others. [2]
Secondly, paying attention to children and adolescents during the
global public health emergency is of special social significance and
clinical value for preventing the occurrence of mental disorders and
adverse events. Humanistic care and psychological interventions for
children are therefore some of the most important components of the
response strategies for the COVID-19 pandemic [3].
Finally, social distancing interventions can be effective against
epidemics but are potentially detrimental for the economy. Businesses
that rely heavily on face-to-face communication or close physical
proximity when producing a product or providing a service are
particularly vulnerable. [4] School closings have sent more than half a
billion children home, according to UNESCO. They could end up missing
months of education and many depend on free school lunch programs.
[5] Physical distancing alone may not be an adequate long term
solution to the crisis, and it is imperative that social and political
leaders, in association with medical experts, come out with reasonable
and scientifically-sound measures and protocols, that safely balance
reducing risk of infection while propping up the national economy.
REFERENCES:
1. Islam N, Sharp SJ, Chowell G, Shabnam S, Kawachi I, Lacey B, et
al. Physical distancing interventions and incidence of corona
virus disease 2019: natural experiment in 149 countries. BMJ
2020;370:m2743.
2. Roser, M., Ritchie, H., Ortiz-Ospina, E. and Hasell, J. (2020) -
"Coronavirus Pandemic (COVID-19)". Retrieved from:
https://ourworldindata.org/coronavirus. Accessed : 1 st October
2020
3. Ye J. Pediatric Mental and Behavioral Health in the Period of
Quarantine and Social Distancing With COVID-19. JMIR Pediatr
Parent2020;3(2):e19867.
4. Koren M, Peto R. Business disruptions from social distancing.
PLoS One. 2020; 15(9): e0239113. doi:
10.1371/journal.pone.0239113
5. Cohen J, Kupferschmidt K. Countries test tactics in ‘war’
against COVID-19. Science 2020;367(6484):1287-1288. DOI:
10.1126/science.367.6484.1287
Competing interests: No competing interests
Dear Editor
It was a pleasure for us to read the article titled “Physical distancing
interventions and incidence of Corona virus disease 2019: Natural
experiment in 149 countries” by Islam et al. [1] in your esteemed
journal. It is a well-written article and quite a relevant one during the
current pandemic crisis. It is a topic of interest for us and we would like
to add a few points which we feel would enrich the article further in
regard to the global response to the COVID-19 pandemic.
As this study mainly intends to pinpoint the way to control the
pandemic spread, personal hygiene measures like hand washing, use of
face mask, gloves etc. along with the physical distancing methods
would seem to have a greater impact on curbing the viral transmission.
While physical distancing protects ourselves from the virus, hand
hygiene and the use of face masks, especially surgical or N95 masks,
both reduces the risk of infection and reduces the risk of infecting
others. [2]
Secondly, paying attention to children and adolescents during the
global public health emergency is of special social significance and
clinical value for preventing the occurrence of mental disorders and
adverse events. Humanistic care and psychological interventions for
children are therefore some of the most important components of the
response strategies for the COVID-19 pandemic [3].
Finally, social distancing interventions can be effective against
epidemics but are potentially detrimental for the economy. Businesses
that rely heavily on face-to-face communication or close physical
proximity when producing a product or providing a service are
particularly vulnerable. [4] School closings have sent more than half a
billion children home, according to UNESCO. They could end up missing
months of education and many depend on free school lunch programs.
[5] Physical distancing alone may not be an adequate long term
solution to the crisis, and it is imperative that social and political
leaders, in association with medical experts, come out with reasonable
and scientifically-sound measures and protocols, that safely balance
reducing risk of infection while propping up the national economy.
REFERENCES:
1. Islam N, Sharp SJ, Chowell G, Shabnam S, Kawachi I, Lacey B, et
al. Physical distancing interventions and incidence of corona
virus disease 2019: natural experiment in 149 countries. BMJ
2020;370:m2743.
2. Roser, M., Ritchie, H., Ortiz-Ospina, E. and Hasell, J. (2020) -
"Coronavirus Pandemic (COVID-19)". Retrieved from:
https://ourworldindata.org/coronavirus. Accessed : 1 st October
2020
3. Ye J. Pediatric Mental and Behavioral Health in the Period of
Quarantine and Social Distancing With COVID-19. JMIR Pediatr
Parent2020;3(2):e19867.
4. Koren M, Peto R. Business disruptions from social distancing.
PLoS One. 2020; 15(9): e0239113. doi:
10.1371/journal.pone.0239113
5. Cohen J, Kupferschmidt K. Countries test tactics in ‘war’
against COVID-19. Science 2020;367(6484):1287-1288. DOI:
10.1126/science.367.6484.1287
Competing interests: No competing interests
Dear Editor
1. May I respectfully submit that physical distance matters not. (Except where mucosal contact is involved).
What matters is the amount of virus which enters the mucosae of the susceptible victim or host. I need not elaborate.
2. Whether the recipient will develop the dis ease will depend upon his immunity. This immunity may be anti-body based - which may be measurable.. It may be cellular- which can not be measured at all at present.
It could also be constitutional - which cannot be measured. You will recall smallpox. Some, admittedly few , persons refused to be vaccinated. Despite exposure to smallpox which carried away their siblings, they survived.
3. Physical distance is, again, not all-important. Imagine X standing 12 inches away from Y.
If the wind is blowing from X to Y,
X has a cough.
Y will catch it.
On the other hand, if the wind blows from Y to X, the virus of X will simply go the other way.
I ask:
1. Should we not ensure that in closed or semiclosed locations ( trains, tubes, aeroplanes, aerodromes, etc, the there should be exhaust pipes sucking air up, not allowing it to enter the respiratory passages of others?
2. Should we not follow South Korea? In Seoul they have installed ultraviolet devices in bus stations, to sterilise the air?
I do hope we British don’t feel embarrassed about copying good practices of South Korea.
Competing interests: No competing interests
Dear Editor
Islam et al. [1] report the success of international governmental lockdown of schools, workplaces, public transport etc. in achieving reductions in covid-19 incidence. As lockdown is released, interventions to control virus-transmitting behaviours transfer from being the responsibility of the state to being the responsibility of each individual to ensure that they maintain physical distance. Using the Behaviour Change Wheel [2] classification, intervention policies transform from using ‘legislation’ and ‘environmental/social planning’ to ‘communication/marketing’ and provision of ‘guidelines’ and the function of the interventions change from ‘restriction’ and ‘environmental restructuring’ to ‘education’ and ‘persuasion’.
As part of the CHARIS project [3], we investigated how individuals who have not had covid-19 see responsibility for getting the disease in a Scottish national representative survey. The research was conducted in the weeks (June 3- June 16), following the first release from the legal requirement to stay at home except for exercise and essential activities (i.e. for basic necessities, daily exercise, basic animal welfare, medical need, travelling for work purposes). We examined the extent to which people aged 16 years or over (n=776) agreed that getting covid-19 could be attributed to their own behaviour, others’ behaviour and poor response from Scottish and UK governments, bad luck and ‘a germ or virus’.
We found that people attributed responsibility to their own and others’ behaviours rather than bad luck. Over 85% agreed or strongly agreed that failure to keep two metres distance and poor hand washing caused covid-19. Fewer, 59.6%, attributed the disease to failure to use face coverings but this was similar to the frequency of agreeing that the cause was ‘bad luck’ (56%). The behaviour of Government was also viewed as causal. Over three quarters of this Scottish sample believe a poor response from the UK Government caused covid-19, whilst only 51.6% have the same belief about the Scottish Government.
We examined whether attributions of causality were associated with performance of protective behaviours. Self-reported adherence behaviours (always or most of the time) was high for keeping two meters distance whether or not they attributed causality to these behaviours (92.0% vs 92.7%) and lower for frequent handwashing (77.9% vs 64.8%). Wearing a face covering, which was advised but not mandatory at this time, was more frequent in those attributing covid-19 to lack of face coverings (38.5% vs 14.3%). Performance of the corresponding behaviour was significantly associated with attributions for hand washing (r=.10, p<.01) and wearing a face covering (r=0.28, p<.01), but not for keeping two metres distance.
These data suggest that the population was attributing responsibility for the spread of covid-19 to their own and others’ behaviour and that these attributions were associated with, and might be causal in determining, their transmission-reducing behaviours.
While government recommendations can influence the covid-19 prevention behaviours of individuals [4] the importance of individual responsibility rather than government control has been identified as key to controlling virus transmission [5].Individual beliefs about the disease and about the behaviours causing its spread, become more important as governments release responsibility to individual citizens. Prior to release from lockdown, a UK survey found that beliefs about what other people were doing was associated with adherence to social distancing [6]. However, as release from lockdown progresses, individuals will have more exposure to how other people behave. Social norms i.e. what other people are doing and what they approve of, are associated with a wide range of preventive behaviours [7]. Rather than top-down, vertical transmission of beliefs from government to individuals, horizontal sharing of ideas and the observation of the behaviour of others is likely become more important.
References
1. Islam, N., Sharp, S. J., Chowell, G., Shabnam, S., Kawachi, I., Lacey, B., ... & White, M. (2020). Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries. BMJ 370.
2. Michie, S., Van Stralen, M. M., & West, R. (2011). The behaviour change wheel: a new method for characterising and designing behaviour change interventions. Implementation science, 6(1), 42.
3. https://www.abdn.ac.uk/iahs/research/health-psychology/charis.php
4. Goldberg, M. H., Gustafson, A., Maibach, E. W., Ballew, M. T., Bergquist, P., Kotcher, J. E., ... & Leiserowitz, A. (2020). Mask-wearing increased after a government recommendation: A natural experiment in the US during the COVID-19 pandemic. Frontiers in Communication, 5, 44.
5. Anderson, R. M., Heesterbeek, H., Klinkenberg, D., & Hollingsworth, T. D. (2020). How will country-based mitigation measures influence the course of the COVID-19 epidemic? The Lancet, 395(10228), 931-934.
6. Smith, L. E., Amlôt, R., Lambert, H., Oliver, I., Robin, C., Yardley, L., & Rubin, G. J. (2020). Factors associated with adherence to self-isolation and lockdown measures in the UK; a cross-sectional survey. medRxiv. preprint doi: https://doi.org/10.1101/2020.06.01.20119040.thi
7. Goldberg, M. H., Gustafson, A., Maibach, E., Linden, S., Ballew, M. T., Bergquist, P., … Leiserowitz, A. (2020). Social norms motivate COVID-19 preventive behaviors. PsyArXiv, https://doi.org/10.31234/osf.io/9whp4
Competing interests: No competing interests
Dear Editor,
In response to our recent article in the BMJ,[1] Fountoulakis et al. noted that our findings of a reduction in the incidence of coronavirus disease 2019 (covid-19) associated with physical distancing interventions were qualitatively in agreement with previously published studies, even though these studies used different effect measures such as reproduction number or transmission potential. The authors also reported that, using similar methodology, their research group found that earlier restrictions on public gatherings was the most effective measure in reducing the covid-19 mortality where all the other physical distancing measures were in place.[2] This finding also aligns with our results that restriction on mass gatherings is a key component of an effective viral containment strategy. These findings strongly support the overall effectiveness of physical distancing interventions despite the differences in study methods an analytic strategies.
Fountoulakis et al. noted that they used covid-19 mortality, as opposed to covid-19 cases, in their study since they considered that “the number of deaths is highly reliable”. We respectfully disagree with this assumption; under-reporting of covid-19 deaths has been reported in many countries including those in the Europe and in the US.[3-7] As we mentioned in our article,[1] covid-19 cases are likely under-reported as are covid-19 deaths.[3-7] However, as noted in the limitations section of our study, we agree with Fountoulakis et al. and Gelman that there are some degrees of heterogeneity across countries in terms of methodology in defining the cases of covid-19, which is inherent to “real-world” data, especially in the context of a pandemic.[8] If we wait for the ‘perfect’ data during a pandemic, we would have to abandon most, if not all, rapid research projects that aim to shed light on the pandemic during these early stages.
In another response, Zadey highlighted two important aspects of the study—the timeline of the ‘lockdown’ in India, and the model fit. This variable 'lockdown' was defined as "a combination of two variables: stay at home regulations and restrictions on movements within a country", as the author noted. The author noted that the India-wide lockdown “in the form of ‘curfew’” was implemented on March 23, 2020, while it was recorded as early as January 26, 2020 in the Oxford covid-19 Government Response Tracker database.[9] We contacted our colleagues of the Oxford covid-19 Government Response Tracker team, and located the specific document that was used for the date for this intervention (more details including the sources of data on these policy interventions are available at https://www.bsg.ox.ac.uk/research/research-projects/coronavirus-governme...). This policy was first recommended by the Government of Kerala in a document published on the 26th of January,[10] which was highly applauded by the World Health Organization for Kerala’s success in handling the pandemic.[11]
As we mentioned in our article, our analysis did not separate out regional vs national measures (largely due to unavailability of systematically collected regional data on covid-19 cases and physical distancing policies across the countries), nor did it examine the adherence to, compliance with, or stringency of the interventions.[1] Also, policy recommendation does not necessarily indicate policy implementations, as we also noted in our article. Therefore, our analysis used the first day of recommendation of the respective policy interventions ('lockdown' in this case), regionally or nationally. However, we acknowledge that regional differences (eg, between states/provinces) can be substantial, especially in larger countries. Since India is one of the largest countries with regional governments, we, therefore, conducted a sensitivity analysis excluding seven largest countries (eg, India), and the main finding remained unchanged.
Zadey and Gelman also raised concerns about the model fit and model parameters. Our interrupted time series model allows for both a change in slope (incidence rate) and a change in level at the time of intervention, the latter of which can therefore look like a "jump" in the fitted line on the incidence graphs (supplementary appendix). We agree with Zadey that change in level may also be relevant in other contexts, but here we chose to focus on change in the slope because we were most interested in the effect over the full post-intervention period examined, and did not anticipate that the intervention would have an immediate effect (i.e. a sudden jump in level) in most countries.
We are of course well aware that the model fits better in some countries than others. A different model may have fit the data better in Canada, for example, but not necessarily in other countries. Using different models in different countries would have precluded the ability to perform a meta-analysis of results across countries.
The graphs shown in the supplementary appendix were provided for additional data on the covid-19 cases for each country up to May 30, 2020. However, our interrupted time series models were restricted up to 30-days post-intervention or May 30, 2020, whichever came first, as specified in our article. The graphs from this analysis are available at https://github.com/shabnam-shbd/COVID-19_Physical_Distancing_Policy/blob..., which shows a considerably better fit in most countries. Again, this model also fits some countries better than others. By presenting graphically the model fit in every country as well as the country-level results, we have been transparent about the approach. The data are available if scientists wish to do more detailed modelling of country-specific data.
We thank all the authors for their interests and scholarly responses to our article.
References
1 Islam N, Sharp SJ, Chowell G, et al. Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries. BMJ 2020;370:m2743. doi:10.1136/bmj.m2743
2 Fountoulakis K, Fountoulakis N, Koupidis S, et al. Factors determining different death rates because of the COVID-19 outbreak among countries. J Public Health 2020;(In Press).
3 Wu J, McCann A, Katz J, et al. 153,000 Missing Deaths: Tracking the True Toll of the Coronavirus Outbreak. N. Y. Times. https://www.nytimes.com/interactive/2020/04/21/world/coronavirus-missing... (accessed 21 Jul 2020).
4 Biswas S. The ‘mystery’ of India’s low Covid-19 death rate. BBC News. 2020. https://www.bbc.com/news/world-asia-india-52435463 (accessed 20 Jul 2020).
5 The Economist. Tourism flows and death rates suggest covid-19 is being under-reported. The Economist 2020. https://www.economist.com/graphic-detail/2020/03/07/tourism-flows-and-de... (accessed 20 Jul 2020).
6 Walsh NP, Krever M. The UK’s ‘coronavirus dashboard’ may be under-reporting deaths significantly. CNN. 2020. https://www.cnn.com/2020/04/07/uk/coronavirus-uk-deaths-intl-gbr/index.html (accessed 21 Jul 2020).
7 Cohen J. Underreporting Of COVID-19 Coronavirus Deaths In The U.S. And Europe (Update). Forbes. https://www.forbes.com/sites/joshuacohen/2020/04/14/underreporting-of-co... (accessed 21 Jul 2020).
8 Zuidgeest MGP, Goetz I, Groenwold RHH, et al. Series: Pragmatic trials and real world evidence: Paper 1. Introduction. J Clin Epidemiol 2017;88:7–13. doi:10.1016/j.jclinepi.2016.12.023
9 Hale T, Petherick A, Phillips T, et al. Variation in government responses to COVID-19. Oxford, UK: : Blavatnik School of Government 2020.
10 Department of Health and Family Welfare, Govt of Kerala. nCorona – Guidelines. 2020. https://web.archive.org/web/20200427215819/http://dhs.kerala.gov.in/wp-c... (accessed 20 Jul 2020).
11 World Health Organization. Responding to COVID-19 - Learnings from Kerala. 2020. https://www.who.int/india/news/feature-stories/detail/responding-to-covi... (accessed 20 Jul 2020).
Competing interests: No competing interests
Dear Editor,
I am concerned that the model does not fit the data and also that the jumps in the fitted model do not make sense, considering the blurring in the underlying process. I was alerted to this by someone who pointed out the graph for Canada on page 84 of the supplementary material. The disconnect between the fit and the data gives me skepticism about the larger claims in the article.
I also have concerns about the data, similar to those raised by the peer reviewers regarding selection effects in who gets tested.
Competing interests: No competing interests
Dear Editor
The recently published research article [1] in BMJ studied the impact of physical distancing interventions on COVID-19 incidence in a multi-country sample using interrupted time-series repression. Lockdown was defined as "a combination of two variables: stay at home regulations and restrictions on movements within a country" in the article. For India, the article claimed the date of lockdown implementation to be somewhere between January 22 and February 12, 2020 (see Data Supplement India plots). However, this is erroneous.
The mobility restrictions of the kind of lockdown in India were placed on March 23 in the form of 'curfew' and then re-inforced as Phase I of lockdown March 25 [2,3]. It is unclear whether this is a typo in the image annotation or an actual incorrect assumption fed into the model. For India, the study has reported an effect size of 1.63 (95%CI: 0.61 to 4.40) for the association between physical distancing interventions and change in IRR (incidence rate ratio). This estimate is likely incorrect if based on the underlying wrong dates. The modeled data for India (see Data Supplement India figures) lacks a change in intercept (or level) a slope pointing to the limited effect of the intervention. It would be crucial to check such errors in for other 148 countries included in the analysis.
Two additional issues about statistical modeling and interpretation are also pertinent to this article.
First, based on the figures presented in the Data Supplement, the model fit seems weak for several countries, clear instances being Iran, Jamaica, Japan. A quantitative metric of model fit needs to be provided to judge if the used model is suitable for the data. In the absence of good model fitting, inferences about the effect of interventions are spurious.
Second, it is unclear why "difference in the slope" (i.e., model coefficient beta-3) was chosen as the primary parameter of interest. Change in level of outcome (or intercept) as coded by model coefficient beta-2 also represents the effect of an intervention. This is seen for instances like Canada (see Data Supplement Canada figures) and others. Consequentially, a lack of change in level at the given time of delay also represents a lack of effect of the intervention, although the slope change might be present. Looking at the difference in level between pre- and post-intervention periods or step-change is particularly crucial in the case of studies like this one, where the data can be modeled nonlinearly undermining the inferences about slope-change [4].
References:
[1] Islam Nazrul, Sharp Stephen J, Chowell Gerardo, Shabnam Sharmin, Kawachi Ichiro, Lacey Ben et al. Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries BMJ 2020; 370:m2743
[2] Patel P, Athotra A, Vaisakh TP, Dikid T, Jain SK; NCDC COVID Incident Management Team. Impact of nonpharmacological interventions on COVID-19 transmission dynamics in India. Indian J Public Health. 2020;64(Supplement):S142-S146. doi:10.4103/ijph.IJPH_510_20
[3] https://thewire.in/covid-19-india-timeline
[4] Lopez Bernal J, Soumerai S, Gasparrini A. A methodological framework for model selection in interrupted time series studies. J Clin Epidemiol. 2018;103:82-91. doi:10.1016/j.jclinepi.2018.05.026
Competing interests: No competing interests
Dear Editor
Recently, a paper has been published by the BMJ [1] suggesting that on average, implementation of any physical distancing intervention was associated with an overall reduction in covid-19 incidence of 13% and that early lockdown was the major determining factor of suppressing the outbreak. This paper is in relative accord with a report suggesting that the lockdown was the strongest measure with 81% or R0 reduction attributed to it, but the methodology of that study was based on self-report data [2]. It is interesting that it also suggested that only multiple measures implemented simultaneously could reduce R0 below 1. Another analysis by the ICL (only in 11 countries) suggested that lockdown was the only efficacious measure [3].
However, the study published by your journal [1] did not take into consideration the great heterogeneity among countries concerning the methodology of identifying new COVID-19 cases. In the vast majority of countries, the method is far from epidemiological and the results reported should not be considered as reliable in order to inform policy decisions. On the other hand, the number of deaths is highly reliable especially in Europe and North America. The finding that physical distancing and especially lockdown resulted in 13% reduction is not only in contrast to the general picture but also to the data. An example could be that Sweden which did not utilize lockdown at all has so far a more than 25-fold higher death rate in comparison to Greece which utilized an early lockdown.
On the other hand, according to a paper in press by our group [4], with data from 40 European countries, which utilizes similar methodology but uses death rates instead of incidence of new cases as the outcome, reported that in countries where all distancing measures are in place, the most effective measure was the early banning of public events. Our results are in accord with a model of spreading where only a few super-spreaders infect large numbers through prolonged exposure (superspreading events) [5 6].
References
1. Islam N, Sharp SJ, Chowell G, et al. Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries. BMJ 2020;370:m2743. doi: 10.1136/bmj.m2743
2. Sypsa V, Roussos S, Paraskevis D, et al. Modelling the SARS-CoV-2 first epidemic wave in Greece: social contact patterns for impact assessment and an exit strategy from social distancing measures. medRxiv 2020:2020.05.27.20114017. doi: 10.1101/2020.05.27.20114017
3. Flaxman S, Mishra S, Gandy A, et al. Report 13: Estimating the number of infections and the impact of non-pharmaceutical interventions on COVID-19 in 11 European countries: https://spiral.imperial.ac.uk:8443/handle/10044/1/77731; 2020 [
4. Fountoulakis KN, Fountoulakis NK, Koupidis SA, et al. Factors determining different death rates because of the COVID-19 outbreak among countries J Public Health 2020;in press
5. Lloyd-Smith JO, Schreiber SJ, Kopp PE, et al. Superspreading and the effect of individual variation on disease emergence. Nature 2005;438(7066):355-9. doi: 10.1038/nature04153 [published Online First: 2005/11/18]
6. Endo A, Abbott S, Kucharski AJ, et al. Estimating the overdispersion in COVID-19 transmission using outbreak sizes outside China. Wellcome Open Research 2020;5(67) doi: 10.12688/wellcomeopenres.15842.1
Competing interests: No competing interests
Re: Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries
Dear Editor,
I am writing this rejoinder regarding the piece declared above published in your online journal on 08 July 2020. Fundamentally, I would like to concede how perceptive the research is on the issue of physical distancing and COVID-19 spread. Reading this article assisted me to comprehend the association between physical distancing and COVID-19 incidence rates and the variation between the distinct physical distancing interventions, the importance of implementing the physical interventions earlier to curb the spread of the virus, and the implication of the results to the policy developers (Islam et al., 2020). Countries that have implemented early physical distancing measures experience low incidences of COVID-19 than their counterparts. Furthermore, the survey indicated a lack of association between public transport restrictions and the virus's spread.
I concur with the research on the significance of physical distancing to prevent the fast spread of COVID-19 and the evidence presented in support of the claims. Research by Quaife et al. (2020) indicated that strict physical distancing measures significantly reduce the incidence of COVID-19 in Sub-Saharan Africa. Physical distancing measures reduce contact between people, preventing the spread of the disease. Besides, Tirachini and Cats (2020) reported that COVID-19 incidence is low in public transport and that appropriate use of face masks is potentially effective in reducing the spread of the contagion. Their study supports the findings presented in this report on the lack of change in transport closure measure implementation.
However, the study did not address the long-term economic and food security problems caused by these interventions: this shows a bias in research since people's well-being concerning food and finances is equally important. The research should have considered both sides of the 'story' instead of leaning on one. It is significant to inform readers of the challenges of enforcing these restrictions for long periods. Thank you.
References
Islam, N., Sharp, S., Chowell, G., Shabnam, S., Kawachi, I., & Lacey, B. et al. (2020). Physical distancing interventions and incidence of Coronavirus disease 2019: Natural experiment in 149 countries. BMJ, m2743. https://doi.org/10.1136/bmj.m2743
Quaife, M., van Zandvoort, K., Gimma, A., Shah, K., McCreesh, N., & Prem, K. et al. (2020). The impact of COVID-19 control measures on social contacts and transmission in Kenyan informal settlements. BMC Medicine, 18(1). https://doi.org/10.1186/s12916-020-01779-4
Tirachini, A., & Cats, O. (2020). COVID-19 and public transportation: current assessment, prospects, and research needs. Journal of Public Transportation, 22(1). https://doi.org/10.5038/2375-0901.22.1.1
Competing interests: No competing interests