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In this paper (Armstrong, Mangtani et al. 2004) the expression we
used for estimating vaccine efficacy (VE) was we have now identified only
approximately consistent. A consistent estimator is:
Where RRu and RRv are the ratios of outcome rates in the flu period
Vs the non-flu period in the vaccinated and unvaccinated respectively.
Re-estimating the VE for all-cause mortality reported in the
published paper changes the estimate little; from 83%(95%CI 9 to 100%)
to 85% (95% 13 to 100) for all-cause mortality, from 80% to 83% for
cardio-vascular and from 79% to 83% for respiratory deaths, with both the
latter two 95% CIs remaining to cover the entire meaningful range (0 to
Although the revision made only a small difference in our data, it
could in other data be more important. Specifically VE2010=RRv.VE2004 i.e.
the originally published estimator is biased by a factor of 1/RRv.
Armstrong, B., P. Mangtani, et al. (2004). "Effect of influenza
vaccination on excess deaths occurring during periods of high circulation
of influenza: cohort study in elderly people." British Medical Journal