How useful are flu vaccines?
Thompson et al.  highlight the correlation between “pneumonia and
influenza” estimated death rates and the percentage of samples positive
for influenza A(H3N2) viruses by week in United States from 1990 to 1998
(cf. Fig. 1, ). This correlation is not in itself inconsistent with the
hypothesis that other factors might substantially or even predominantly
contribute to the mortality seasonal burden. Apart from the respiratory
illnesses caused by the increase of environmental pollutants during the
winter season , it is worth remembering that “Cold weather alone causes
striking short term increases in mortality, mainly from thrombotic and
respiratory disease”, even without an influenza epidemic .
This is in agreement with the generally recognized circumstance that
“isolation of human influenza viruses in the blood has been reported only
rarely” and that the immediate cause of death in almost all cases is
not the viral infection itself but an indirect “complication”, like
secondary bacterial pneumonia.
That there is a serious problem here for the conventional estimates
of the “pneumonia and flu” death rates is widely accepted. For instance,
one member of the Simonsen et al. team, Jonathan Dushoff, published a few
months ago a useful note emphasizing: “Approaching a consensus on the
health and mortality burden of influenza, and on the cause of winter
excess mortality in general, is an important scientific and public policy
goal. For this to happen, further progress is needed in several areas”,
and concluding: “The contribution of influenza to morbidity and mortality
– and, more broadly, cataloging the causes of daily and season excess
deaths and hospitalizations – remain as unresolved questions with
important scientific and public-health implications." ()
More should be done in the way of epidemiological research to assess
the relative weight of all plausible factors and to ascertain how
frequently the flu viruses are actually involved in the fatal outcomes.
Most importantly, it must be pointed out that the so-called
“complications” are also linked to influenza-like illness (ILI), which is
“clinically indistinguishable from influenza” . ILI, defined as a
symptomatic syndrome, is in fact caused by hundreds of different agents,
including RSV (respiratory syncytial virus), picornaviruses,
parainfluenza, hMPV (human metapneumovirus), coronaviruses etc.(see e.g.
Now, an important public health issue arises at this point, since
vaccine is protective only against two of the agents causing symptomatic,
clinical flu. It follows that even if clinical flu were the underlying
cause of seasonal differences in “pneumonia and influenza” death rates,
this would not in itself provide a solid ground for the mass flu
It is interesting that Doshi’s critics (, ) seem to evade the
crucial issue of the extent the flu vaccines are succeeding in preventing
clinical flu. The results of two recent meta-analyses are by no means
encouraging (, ). In , which deals with 65+ individuals (one of
the high priority groups for mass vaccination according to the CDC), it is
stated that “the usefulness of vaccines on the community [as opposed to
long-term care facilities] is modest”; in  the effectiveness of
vaccines in children younger than 2 (inactivated vaccines) or older than 2
(both inactivated and live attenuated vaccines) was found to be “low”. One
of the main reasons given to explain these disappointing results is that
“vaccines are specifically targeted at influenza viruses and are not
designed to prevent other causes of influenza-like illness”.
In an interview the senior author of  and , Dr. Tom Jefferson,
put the issue in a refreshingly explicit way: "The vaccine doesn't work
very well at all. [...] Vaccines are being used as an ideological weapon.
What you see every year as the flu is caused by 200 or 300 different
agents with a vaccine against two of them. That is simply nonsense."
So it appears that the picture, not only at a theoretical level but
even as regards “public health efforts”, is much more complicated than
that provided by the NIH and CDC representatives.
 Thompson WW, Shay D, Weintraub E, Brammer L, Meltzer M, Cox N,
Bresee J. "Are estimates of influenza-associated deaths in the US really
just PR?". BMJ [rapid response] (18 Jan 2006)
<http://bmj.com/cgi/eletters/331/7529/1412#126308> (retrieved 23 Jan
 Crowe D. "The Peril of Correlation". BMJ [rapid response] (14 Jan
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 Donaldson G. C., W R Keatinge W. R., “Excess winter mortality:
influenza or cold stress? Observational study”, BMJ, Vol. 324, pp.89-90
(12 Jan 2002)
 Dushoff J. “Assessing influenza-related mortality: comment on
Zucs et al.”, Emerging Themes in Epidemiology, 2005, 2:7,
 Kelly H., Birch C. “The causes and diagnosis of influenza-like
illness”, Australian Family Physician Vol. 33, No. 5, May 2004, pp. 305-9
 Jefferson T., Rivetti D., Rivetti A., Rudin M., Di Pietrantonj
C., Demicheli V., “Efficacy and effectiveness of influenza vaccines in
elderly people: a systematic review”, Lancet, Vol. 366, pp. 1165-74 (1 Oct
 Jefferson T., Smith S., Harnden A., Rivetti A, Di Pietrantonj C.,
“Assessment of the efficacy and effectiveness of influenza vaccines in
healthy children: systematic review”, Lancet, Vol. 365, pp. 773-80 (26 Feb
 Gardner A., “Flu Vaccine Only Mildly Effective in Elderly”,
(retrieved 24 Jan 2006)
 Simonsen L, Taylor R, Viboud C, Dushoff J, Miller M. "US Flu
Mortality Estimates Are Based on Solid Science". BMJ [rapid response]
(2006) <http://bmj.com/cgi/eletters/331/7529/1412#125778> (retrieved
11 Jan 2006).
Competing interests: No competing interests