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Effect of influenza vaccination on excess deaths occurring during periods of high circulation of influenza: cohort study in elderly people

BMJ 2004; 329 doi: https://doi.org/10.1136/bmj.38198.594109.AE (Published 16 September 2004) Cite this as: BMJ 2004;329:660

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Correction to estimator for vaccine efficacy

Correction

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:

VE=(RRu-RRv)/(RRu-1)

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
100).

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.

A derivation of the new estimator and its relationship to the old one
is available from ben.armstrong@lshtm.ac.uk.

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
329(7467): 660.

Competing interests:
None declared

Competing interests: No competing interests

23 June 2010
Ben G Armstrong
Professor of Epidemiological Statistics
Sam Pattenden and Punam Mangtani
LSHTM, London WC1E 7HT
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