Intended for healthcare professionals

Analysis

Calibrated response to emerging infections

BMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b3471 (Published 03 September 2009) Cite this as: BMJ 2009;339:b3471

Mass vaccination against swine flu; could it cause more harm than good?

Dear Editors

Mass vaccination against swine flu; could it cause more harm than
good?

Dear Sir,

Doshi (1) appropriately highlights the need for public health
responses to take into account the severity of any new infection as well
as its ability to spread. US Department of Health and Human Services, too,
in 2005 called for a graduated response in its pandemic preparedness plan
(2). It introduced a five-step "pandemic severity index" stratified by the
case fatality ratio (category 1 is for a pandemic with case fatality ratio
<_0.1. p="p"/> This “swine flu” pandemic, while it spread readily, appears to have a
very low mortality rate (less than 1 per 10,000 infected) (3,4). It thus
seems inappropriate that we should rush into what must be the world’s
largest ever mass vaccination program but with vaccines that have had
potentially less than optimal safety and efficacy studies performed.
Rolling it out in multi-dose vials also has the inherent increased risk of
cross infections with bacteria and blood borne virus infections (5,6).

We need to be sure with any vaccination program that the benefits
will substantially outweigh the risks. That is not at all clear with this
pandemic. Inappropriate levels of fear have already pushed us into
inappropriate responses. One example is the gross overuse of oseltamivir.
Fear has caused many people who should have stayed home and recovered
uneventfully with a mild illness, to seek medical help and treatment.
These actions likely spread infection in the facilities they visited and
while travelling. In addition such behaviour limits access to medical care
to those who had risk factors and did need to be seen promptly for either
therapy of prophylaxis.

The Northern hemisphere is about to enter the autumn and winter
seasons. There are now good data available from New Zealand (7) and
Australia (3,4) on what might be expected in winter when unvaccinated
populations are exposed to this new variant strain of influenza.

The best up to date data that is age stratified is from NSW Health
(3). It and the other Australian data (4) show now that this flu episode
is close to ending (it peaked early and unexpectedly in mid July). The
data show that this flu season has not been much worse overall than 2007
(although certain subgroups e.g. pregnant women have been overrepresented
in hospital and ICU admissions).

The death rate in the population was low, about 0.6 per 100,000
people (3,4).

Overall admission rates were not high either compared to seasonal
influenza (usually around 15 per 100,000 per). ICU admissions were 2.7 per
100,000 population. There are about 200,000 pregnant women at any one
time in Australia. My estimate for death was about 2 per 100,000 pregnant
women.

While hospital admission rates are available broken down by age
group, similar data is not available for deaths. My calculations of deaths
by age group are based on the data in these reports (Table 1).

Worldwide we are about to rollout one of the biggest and most rapid
vaccine campaigns ever undertaken. Reported inactivated vaccine efficacy
is between 50 to 80% (8). Thus for every 1 million people vaccinated we
will decrease the number of deaths from 6 to 2 or 3 people. We will also
prevent between 75 to 120 hospital admissions and 13 to 22 ICU admissions.

Given the relative lack of infections we are seeing in the elderly,
it appears that most people over 60 years are already immune (presumable
from previous H1N1 infection). Now also probably at least 20% of under-60
year old Australians have already been infected. Thus potentially only
about 60% of the Australian population may benefit from mass vaccination
if H1N1 returns next winter.

We need to weigh this against the risks of vaccination. There will
probably be between 1 to 2 additional episodes of Guillain-Barré syndrome
per million vaccine recipients (5,8). If we have a repeat of the 1976 US
swine flu vaccination roll-out then there may be 10 cases per million
vaccine recipients. We also need to estimate how many bacterial and blood
borne virus infections we might expect from the use of multi-use vials
(5,6).

Australia is approaching its spring. There is no need here to rush
into a mass vaccination programme particularly using multi-dose vials. In
the Northern hemisphere, rapid assessment of different age groups and at-
risk groups is needed re their risk and rates of death or severe
infection. This is to ensure that vaccination policy is appropriately
targeted to the threat of H1N1 and based on the extensive data now
available from winter in the Southern Hemisphere and the previous summer
in the Northern hemisphere. Mass vaccination will not be appropriate
unless likely benefits substantially outweigh likely risk in many of the
age groups.

Table 1

Number of admissions Deaths admissions rate deathrate
Under 40 724	5	17.9	0.12
40-49	132	8	13.3	0.81
50-59	186	15	20.9	1.69
60-69	78	7	11.9	1.07
70+	70	11	10.5	1.64

Total	1190	46	17.1	0.66

Rate per 100,000 population (NSW) (3)

References

1. Doshi P. Calibrated response to emerging infections. BMJ. 2009 Sep
3;339:b3471. doi: 10.1136/bmj.b3471.
http://www.bmj.com/cgi/content/full/bmj.b3471?ijkey=tKcb8W6KUoHXzPC&keyt....
[accessed September 11, 2009].

2. Interim Pre-pandemic Planning Guidance: Community Strategy for
Pandemic Influenza Mitigation in the United States. February 2007. CDC
Atlanta. http://www.flu.gov/professional/community/mitigation.html
[accessed September 11, 2009].

3. Weekly Influenza Epidemiology Report, NSW. Including H1N1
influenza 09
Prepared by the Population Health Division, 2 September 2009. NSW Health.
http://www.emergency.health.nsw.gov.au/swineflu/resources/pdf/case_stati...
[accessed September 11, 2009].

4. AUSTRALIAN INFLUENZA SURVEILLANCE SUMMARY REPORT No.16, 2009,
REPORTING PERIOD: 22 August 2009 – 28 August 2009.
http://www.healthemergency.gov.au/internet/healthemergency/publishing.ns...

5. Sweet M and Collignon P. Why can’t we have a rational discussion
about the merits of pandemic flu vaccination? August 31, 2009. Croakey.
http://blogs.crikey.com.au/croakey/2009/08/31/why-cant-we-have-a-rational-
discussion-about-the-merits-of-pandemic-flu-vaccination/?source=cmailer
[accessed September 11, 2009].

6. Drain PK, Nelson CM, Lloyd JS. Single-dose versus multi-dose
vaccine vials for immunization programmes in developing countries. Bull
World Health Organ. 2003;81(10):726-31.

7. Baker MG, Wilson N, Huang QS, Paine S, et al. Pandemic influenza
A(H1N1)v in New Zealand: the experience from April to August 2009.
EuroSurveill. 2009 Aug 27;14(34).
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19319
[accessed September 11, 2009].

8. Demicheli V, Di Pietrantonj C, Jefferson T, Rivetti A, Rivetti D.
Vaccines for preventing influenza in healthy adults (Review). Cochrane
collaboration. The Cochrane Library, Issue 2. Available online at:
http://www.cochrane.org/reviews/en/ab001269.html
[accessed September 11, 2009].

Competing interests:
None declared

Competing interests: Table 1Number of admissions Deaths admissions rate deathrateUnder 40 724 5 17.9 0.1240-49 132 8 13.3 0.8150-59 186 15 20.9 1.6960-69 78 7 11.9 1.0770+ 70 11 10.5 1.64Total 1190 46 17.1 0.66Rate per 100,000 population (NSW) (3)

11 September 2009
Peter J Collignon
ID Physician and Microbiologist
Canberra 2607