The unequal distribution could affect estimates, as a drug's overall effectiveness is usually adjusted to account for the variation in efficacy among age groups.įor example, England's narrow range for Pfizer-vaccinated adults potentially means less confidence in how the country's data applies to older people.

In Israel, everyone received Pfizer's vaccine. One big difference between the data is that Pfizer's drug wasn't distributed equally in England and Israel.Īlthough vaccination was rolled-out by age group in both countries, in England almost all adults over 40 years received the Oxford/AstraZeneca vaccine, while many younger people were given the option of Pfizer.

And because a vaccine works by prompting an immune response, its effectiveness will vary among different age groups.

Age GroupsĪnother possible reason for the discrepancy is the impact of age, which could introduce errors into the statistics used to estimate the vaccine's efficacy.Ī person's susceptibility to Covid is influenced by age, with the elderly being more vulnerable to developing disease and children being less susceptible - in part thanks to their stronger immune systems. The average for those four vaccination months gives Pfizer's vaccine an overall figure of 41% effective.Īccording to sampling of the Israeli population since mid-June, the prevalence of Delta is 93%, which suggests that Pfizer's figure largely reflects effectiveness against that variant.īy contrast, the study led by Public Health England reported efficacy based on everyone who tested positive for Delta over a 7-month timeframe (26 October 2020 and ) and doesn't mention when those 122 people had been vaccinated.Īt first glance then, Israel's data looks more accurate as it shows Pfizer's effectiveness in finer detail - but other factors undermine that conclusion. Over a 4-week period (20 June to 17 July 2021), Pfizer's general effectiveness decreased as the time before exposure increased: efficacy was 79% for those who received their second dose in April, 69% for March, 44% for February, and 16% for people who were fully-vaccinated back in January.

How effective is privazer