Economy 25 August 2021, 1:10pm

COVID-19 vaccine protection abates within six months - UK researchers

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Protection against COVID-19 offered by two doses of the Pfizer/BioNTech and the Oxford/AstraZeneca coronavirus vaccines begins to fade within six months, underscoring the need for booster shots, according to researchers in Britain, Reuters reported on Wednesday.

Analysis of data in Britain's ZOE COVID study included:

411,642 test results from users who were doubly vaccinated with the Pfizer mRNA vaccine at the time of the infection
709,486 test results from users who were doubly vaccinated with the AstraZeneca vaccine
76,051 test results from users who were not yet vaccinated at the time of the infection

It was found that after five to six months, the effectiveness of the Pfizer jab at preventing COVID-19 infection in the month after the second dose fell from 88% to 74%.

For the AstraZeneca vaccine, effectiveness fell from 77% to 67% after four to five months.

The study was based on data from more than 1.2 million test results, making this one of the largest real-life vaccine effectiveness studies on record. The authors stressed that these figures have been adjusted to give an average risk of infection reduction across the population. But because we are all unique and our immune systems may respond in different ways to the vaccine, there will be variation in individual levels of immunity and infection risk.

Previous analysis of data has suggested that vaccines provide protection for at least six months.

The data from the ZOE COVID Study provides vital information about how COVID vaccines are performing ‘in the wild’, outside the controlled confines of clinical trials.

“A reasonable worst-case scenario could see protection below 50% for the elderly and healthcare workers by winter," said Tim Spector, principal investigator for the ZOE COVID study.

"With 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," he warned.

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.

"It's bringing into focus this need for some action. We can't just sit by and see the protectiveness slowly waning whilst cases are still high and the chance of infection still high as well," Spector told BBC television.

Britain is starting to plan for a COVID-19 vaccine booster campaign later this year after top vaccine advisers said it might be necessary to give third shots to the elderly and most vulnerable from September.

The authors of the ZOE COVID Study stressed that

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.

"Importantly, not only does your vaccine help to protect you, it also protects those around you who aren’t yet vaccinated. This includes children and people with weakened immune systems who don’t respond as well to the vaccine."

Another report published by the U.S. Centre for Disease Control and Prevention (CDC) shows that the effectiveness of Covid-19 vaccines among front-line workers declined to 66% after the Delta variant became dominant, compared with 91% before it arose, Bloomberg reported.

Just like the British study, the CDC also stressed that the vaccines are still protective, and the finding must be interpreted with caution, as vaccine effectiveness might wane over time and the estimates of efficacy were imprecise.

The British study also noted that the discovery that vaccine-induced immunity against COVID-19 fades over time is not unexpected, although it might require a new vaccination strategy over the coming months.

The CDC observational study tracked more than 4,000 health-care workers, first responders, and other front-line personnel in eight U.S. locations across six states from December 2020 to August 2021.

They were tested weekly for Covid infection, and about 83% were vaccinated. About two-thirds of those vaccinated had received the Pfizer-BioNTEch shot, 2% received Johnson & Johnson's, and the rest received the Moderna vaccine.

Overall, vaccinations were estimated to be 80% effective in preventing infection during the study period.