Research suggests protection from Covid vaccine drops after six months
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New research suggests protection provided by two doses of the Pfizer/BioNtech and Oxford/AstraZeneca Covid vaccines could wane within six months.
The latest analysis from the Zoe Covid study showed the Pfizer jab has 88pc effectiveness a month after the second dose, but after five to six months protection decreased to 74pc. The AstraZeneca vaccine was shown to offer 77pc protection a month after the second dose, decreasing to 67pc after five months.
The study used data from more than 1.2m test results and participants. This new research follows an earlier mid-term efficacy trial by Pfizer, which showed a 96.2pc risk reduction in infection two months after the second dose. After four months, this study showed an 83.7pc reduction in protection following a second dose
Real world analysis would be expected to show less protection than clinical trials, and the vaccines were not trialled against the now dominant Delta variant of the virus.
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.
Zoe 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 have been adjusted to give an average risk of infection reduction across the population.
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While protection appears to decrease steadily, individual risk may vary due to individual variation in antibody duration, researchers say.
Across the UK, vaccines were rolled out among the older and the most vulnerable in society along with health workers before rolling out vaccines to younger age groups across the UK.
This means the majority of people who had their second dose five to six months ago will be older or considered vulnerable due to other health reasons.
This suggests these people are now likely to be at increased risk of Covid-19 compared to those vaccinated more recently.
Researchers say that in order to confidently illustrate how vaccine effectiveness changes over time in different age groups, more data is needed over a longer period of time.
Professor Tim Spector, lead scientist on the Zoe Covid Study app, said: "In my opinion, a reasonable worst-case scenario could see protection below 50pc 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.
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"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."