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Rapid response to:


Cellular immune responses to covid-19

BMJ 2020; 370 doi: (Published 31 July 2020) Cite this as: BMJ 2020;370:m3018

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COVID-19 and seasonal influenza: dual burden and epidemic intelligence from Flu vaccine

Dear Editor,

COVID-19 and seasonal influenza: dual burden and epidemic intelligence from flu vaccine

Sewell et al. briefly highlights the role of humoral and T-cell-mediated immunity to fight against COVID-19.[1] As we wait for a successful vaccine against COVID-19 following recent successful phase-1 and phase-2 vaccine trials,[2,3] there is a crucial challenge of subsequent waves of COVID-19 including a winter wave. For the first time in recent history, we are on the verge of a dual burden of COVID-19 pandemic and a seasonal influenza epidemic.[4] Each of these can result in life-threatening illnesses and death, especially in vulnerable populations (e.g., elderly, people with underlying conditions, ethnic minority). With available evidence of a beneficial effect of physical distancing,[5] it was suggested that England may need another lockdown in winter.[6] In the absence of a successful vaccine against COVID-19, what role can the flu vaccine play to mitigate the dual burden of COVID-19 and seasonal influenza?

Healthcare burden, and case identification:
COVID-19 and seasonal influenza share similar signs and symptoms. Therefore, in settings with a low Flu vaccination coverage, more patients would seek medical help with very similar symptoms,[7] making it more challenging for the healthcare providers to distinguish between seasonal influenza and COVID-19. This would, consequently, (a) require more testing kits, which are already scarce in many countries around the world, (b) increase the burden on healthcare providers, and (c) increase the exposure of seasonal influenza patients to SARS-CoV-2.

A higher coverage of Flu vaccination would help reduce the rate of hospitalizations due to severe influenza, especially in elderly population.[9] This would reduce the burden on healthcare system and help allocate more resources available to tackle COVID-19 epidemic. It would also reduce the exposure of elderly patients with seasonal influenza to SARS-CoV-2.

Flu vaccine and epidemic intelligence:
A higher flu vaccine coverage may also provide some epidemic intelligence regarding (i) potential cross-immunity of Flu vaccine against COVID-19, and (ii) emergence of potential new viral strain(s). The potential cross-immunity, which is still unknown, can be hypothesised if we see a substantial difference in the number of COVID-19 cases between settings with high- and low-coverage of flu vaccine. However, if we see an unusually high proportion of people with influenza-like symptoms even in settings with high Flu vaccine coverage, and if we find that these patients are not affected by SARS-CoV-2, we may suspect the emergence of potentially (mutated) new strain(s) of seasonal influenza, or COVID-19, or a new virus species. Such epidemic intelligence will be invaluable for early detection of, and preparation for, a potential epidemic/pandemic. Therefore, expanding the Flu vaccine coverage ahead of seasonal influenza season would be invaluable in tackling the dual burden of COVID-19 pandemic and seasonal influenza epidemic.

1 Sewell HF, Agius RM, Stewart M, et al. Cellular immune responses to covid-19. BMJ 2020;370. doi:10.1136/bmj.m3018
2 Folegatti PM, Ewer KJ, Aley PK, et al. Safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase 1/2, single-blind, randomised controlled trial. The Lancet 2020;:S0140673620316044. doi:10.1016/S0140-6736(20)31604-4
3 Zhu F-C, Guan X-H, Li Y-H, et al. Immunogenicity and safety of a recombinant adenovirus type-5-vectored COVID-19 vaccine in healthy adults aged 18 years or older: a randomised, double-blind, placebo-controlled, phase 2 trial. The Lancet 2020;:S0140673620316056. doi:10.1016/S0140-6736(20)31605-6
4 Belongia EA, Osterholm MT. COVID-19 and flu, a perfect storm. Science 2020;368:1163–1163. doi:10.1126/science.abd2220
5 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
6 O’Dowd A. Covid-19: England could need another lockdown in winter, say government’s chief advisers. BMJ 2020;:m2909. doi:10.1136/bmj.m2909
7 Heymann DL, Shindo N. COVID-19: what is next for public health? The Lancet 2020;395:542–5. doi:10.1016/S0140-6736(20)30374-3
8 Padula WV. Why Only Test Symptomatic Patients? Consider Random Screening for COVID-19. Appl Health Econ Health Policy 2020;:1–2. doi:10.1007/s40258-020-00579-4
9 Flannery B, Chung JR, Ferdinands J, et al. Preliminary estimates of 2018–19 seasonal influenza vaccine effectiveness against medically attended influenza from three U.S. networks. 2019;201902.

Competing interests: No competing interests

31 July 2020
Nazrul Islam
University of Oxford
Nuffield Department of Population Health, University of Oxford, Oxford, UK