The Pfizer jab was 88 per cent effective at preventing Covid-19 infection a month after the second dose, but this fell to 74 per cent after five to six months – a drop of 14 percentage points in four months.
The protection provided by two doses of the Pfizer or AstraZenecacoronavirus vaccines begins to wane within six months, new research suggests.
In a reasonable “worst-case scenario”, protection could fall to below 50 per cent for the elderly and healthcare workers by winter, analysis from the Zoe COVID study found.
With the AstraZeneca vaccine, there was a protection against infection of 77 per cent one month after the second dose. This decreased to 67 per cent after four to five months, suggesting a fall of 10 percentage points over three months.
Pfizer’s mid-term efficacy trial observed an initial 96.2 per cent risk reduction in infection up to two months after the second dose. There was an 83.7 per cent reduction more than four months after the second dose, a 12.5 percentage point risk reduction.
The results of the study, which drew on more than 1.2 million test results and participants, will intensify calls for an Autumn booster vaccination campaign to help prevent a spike in cases and hospitalisations.
Other countries have already set out plans for booster campaigns. Earlier this month, the Biden administration announced that third inoculations will be available to most US adults from September.
Israel has already been administering booster shots for those aged over 50 following a surge in cases. Research conducted by the country’s health ministry also suggested the protection conferred by the Pfizer vaccine had begun to wane in the vulnerable population.
The vaccine rollout in the UK prioritised the elderly and vulnerable, beginning with care home residents and those aged over 80. As many will have received their jab over six months ago, the Zoe study suggests they are likely to be vulnerable to infection this Winter compared with those vaccinated more recently.
Real world analysis would be expected to show less protection than clinical trials, and the vaccines in the Zoe study were not trialled against the now dominant Delta variant of the virus.
Professor Tim Spector, lead scientist on the Zoe Covid Study app, said: “In my opinion, a reasonable worst-case scenario could see protection below 50% for the elderly and healthcare workers by winter.
“If high levels of infection in the UK, driven by loosened social restrictions and a highly transmissible variant, this scenario could mean increased hospitalisations and deaths.
“We urgently need to make plans for vaccine boosters, and based on vaccine resources, decide if a strategy to vaccinate children is sensible if our aim is to reduce deaths and hospital admissions. Waning protection is to be expected and is not a reason to not get vaccinated.
“Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to get fully vaccinated.”
Yesterday, the UK government signed a deal to get 35 million more doses of the Pfizer vaccine for the second half of next year, in a clear indication that ministers are preparing for regular ongoing booster programmes. The Joint Committee on Vaccination and Immunisation is expected to rule soon on a booster plan for the UK.
The Zoe Covid Study launched an app feature on December 11, 2020 to enable logging of Covid-19 vaccines and monitor real-world side-effects and effectiveness in its cohort of over a million active users.
It used data from vaccines which were logged from December 8 last year to July 3, 2021 and from infections which occurred between May 26 this year when the Delta variant became dominant, and July 31.
The results of the study have been adjusted to give an average risk of infection reduction across the population.
