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Covid Pfizer and AstraZeneca vaccine protection reduces after six months, study suggests

“Waning protection is to be expected and is not a reason to not get vaccinated,” a professor said.

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THE PROTECTION PROVIDED by two doses of the Pfizer/BioNTech and the Oxford/AstraZeneca coronavirus vaccines starts to wane within six months, new research suggests.

A reasonable worst-case scenario could see protection fall to below 50% for the elderly and healthcare workers by winter, an expert has said.

The Pfizer jab was 88% effective at preventing Covid-19 infection a month after the second dose.

But after five to six months the protection decreased to 74%, suggesting protection fell 14 percentage points in four months, latest analysis from the UK’s Zoe Covid study indicates.

With the AstraZeneca vaccine, there was a protection against infection of 77% one month after the second dose.

After four to five months protection decreased to 67%, suggesting protection fell by 10 percentage points over three months.

The study drew on more than 1.2 million test results and participants.

The mid-term efficacy trial by Pfizer observed an initial 96.2% risk reduction in infection (up to two months after the second dose).

There was an 83.7% reduction more than four months after the second dose, a 12.5% risk reduction.

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.”

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 11 December 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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In Ireland, the National Immunisation Advisory Committee (NIAC) is considering whether booster vaccines will need to be administered in the autumn to provide extra immunity.

The World Health Organization has criticised richer countries planning to administer booster shots, arguing that the supplies should go to developing countries instead.

While protection appears to decrease steadily, individual risk may vary due to individual variation in antibody duration, researchers say.

In most countries including Ireland, Covid-19 vaccines were rolled out among older people and the most vulnerable in society along with health workers before rolling out vaccines to younger age groups.

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.

About the author:

Press Association

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