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Seasonal Flu Efficacy

Paul F Hope made this Freedom of Information request to Public Health England

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Dear Public Health England,

There is a distinction between the epidemiologic concepts of vaccine efficacy and vaccine effectiveness. The mathematical deduction of protective vaccine efficacy is nearly 100 years old, having been proposed by Greenwood and Yule in 1915.
The outcome data (vaccine efficacy) generally are expressed as a proportionate reduction in disease attack rate (AR) between the unvaccinated (ARU) and vaccinated (ARV) study cohorts and can be calculated from the relative risk (RR) of disease among the vaccinated group with use of the following formulas. Vaccine efficacy is defined as the reduction in the incidence of a disease among people who have received a vaccine compared with the incidence in unvaccinated people.

Formula:
VE = (ARU - ARV)/ARU (x 100)
where
VE = vaccine efficacy;
ARU = attack rate in the unvaccinated population
and
ARV = attack rate in the vaccinated population.

Vaccine effectiveness is often confused with vaccine efficacy but should be viewed as a distinctly different, although a related, concept. Essentially, vaccine effectiveness is a view of how a vaccine (which may have already proven to have high vaccine efficacy) reduces disease in a population. The outcome data (vaccine effectiveness) are expressed as a rate difference, with use of the odds ratio (OR) for developing infection despite vaccination:

Formula:
Effectiveness = (1-OR) x100

Recently Public Health England has been quoted in the press regarding the seasonal influenza vaccination as announcing that this year’s flu vaccine protected only 3% of patients and it normally protects at least 60% of patients.
An example of a quotation is in the Independent , “New research from Public Health England (PHE) has found the vaccine protects just three in a hundred people – compared to 50 per cent effectiveness typically seen in recent years.” http://www.independent.co.uk/life-style/...

If this year’s seasonal vaccine protected 3% of the vaccinated population in would be considered a success therefore I have to assume that these quotations refer to efficacy. Therefore the calculation of efficiency to return 3% = (10-9.7)/10*100. Where ARU= 10 and ARV=9.7
Therefore with a 3% efficacy only a third of 1% of the population will benefit from seasonal vaccination.

Under the freedom of information act please supply me with:

1. Public Health England’s efficacy calculations for this year’s seasonal flu vaccination.
2. When did Public Health England calculate this year’s flu vaccination efficacy?
3. Who did Public Health England inform when they calculated this year’s seasonal flu efficacy?
4. What press releases were in relation to their efficacy calculations?
5. When were these press releases?
6. Has the Public Health England stated anywhere that the vaccine “protects three in a hundred people – compared to 50 per cent effectiveness typically seen in recent years”?
7. Have the Public Health England attempted to correct this statement (6) attributed to them.

Yours faithfully,

Paul F Hope

FOI, Public Health England

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Dear Mr Hope

Please find Public Health England's response to your freedom of information request.

Kind Regards

Freedom of Information Officer
Public Health England
Tel: 020 8327 6920
www.gov.uk/phe 

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