Report of 8% vaccine efficacy for elderly is unreliable

The German federal government has responded to a claim in the German newspaper Handelsblatt that suggested the Oxford-AstraZeneca vaccine was 8% effective among over 65s. 

Handelsblatt attributed this information to the federal government. However, the German Federal Ministry of Health told Full Fact it “cannot confirm recent reports of reduced efficacy of the AstraZeneca vaccine”, adding:

“At first glance, it seems that two things have been confused in the reports: About 8% of the subjects in the AstraZeneca efficacy trial were between 56 and 69 years of age, and only 3 to 4 percent were over 70 years of age.

“However, this does not imply an efficacy of only 8% in the elderly.”

The claim has also been denied by the University of Oxford and AstraZeneca.

After this article was first published, Handelsblatt published a paper from Germany’s federal disease control agency, the Robert Koch Institute (RKI), including its calculations on the vaccine’s efficacy data submitted by the manufacturers. These appeared to show the vaccine was just 6.3% effective among over 65s.

This is close to 8%. However this number shouldn’t be taken at face value. 

Vaccine efficacy is calculated by comparing the number of vaccinated people who catch the disease to the number of unvaccinated people who catch the disease.

Because you might not expect many people to become exposed to and catch the disease, even among the unvaccinated group, you need a large number of trial participants to accurately observe any effect. 

But, in this case, there were only 660 over 65s in the trial, roughly half of whom were vaccinated and half of whom were not.

There was only one infection in each group.

With sample sizes this small, the margin of error around that 6.3% figure was huge, from the vaccine being 94% effective among over 65s to 1405% ineffective. 

By comparison, the RKI deemed the efficacy among all people in the trial to be between 54.8% and 80.6% with 70.4% as the central estimate. 

Subsequently Germany’s vaccination committee only recommended the vaccine for under 65s, saying: “There is not yet sufficient data available to evaluate the vaccine efficacy for the age of 65 years and older.”

The European Medicines Agency recommended authorising the AstraZeneca vaccine for all age groups.

In December, research published in the Lancet showed that older adults who received the vaccine showed a similar immune response to younger adults. 

Prof Stephen Evans, Professor of Pharmacoepidemiology at London School of Hygiene & Tropical Medicine, said: “The randomised data on immunogenicity does not suggest that there will be notably lower efficacy at older ages for the Oxford/ AstraZeneca vaccine.” However, he noted that efficacy data for older adults is more limited as older adults were recruited into trials later.