Delta variant of SARS-CoV-2: Can vaccine boosters stop its spread?

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The Delta variant of SARS-CoV-2, the virus that causes Covid-19, is more transmissible than preexisting variants, and it has rapidly become the dominant variant in several countries, including India and the United Kingdom.

Some reports suggest that existing Covid-19 vaccines may be less effective in preventing infection with Delta. Can additional booster shots help?

Over the past few months, the Delta variant of SARS-CoV-2 has spread widely in countries around the world, becoming the dominant variant in many places.

Its rapid spread has recently led countries, such as Australia, to reinforce strict lockdowns, as emerging dataTrusted Source suggest the variant is more infectious than preexisting ones, such as the Beta variant, and that it may be able to bypass existing Covid-19 vaccines in some cases.

Prof. Sir Andrew Pollard, head of the Oxford Vaccine Group, which has contributed to the development of the Oxford-AstraZeneca vaccine, has even commented that, in his opinion, the highly transmissible Delta variant has made achieving herd immunity an impossibility.

“The Delta variant will still infect people who have been vaccinated. And that does mean that anyone who’s still unvaccinated at some point will meet the virus […], and we don’t have anything that will [completely] stop that transmission,” he told The Guardian.

Additionally, recent data have also suggested the immunity provided by Covid-19 vaccines fades considerably over time, which also means vaccinated individuals become more susceptible to infection with SARS-CoV-2.

However, some scientists and pharmaceutical companies argue that offering an additional booster shot of some of the most widely authorized Covid-19 vaccines could provide an effective way to keep the Delta variant at bay.

But what does the evidence say so far, and how are countries worldwide responding to the notion of incorporating additional booster shots in their Covid-19 vaccination campaigns?
While published data on the effectiveness of Covid-19 vaccine boosters against the Delta variant are not yet available, some of the pharmaceutical companies that produce and distribute Covid-19 vaccines have announced that recent clinical trials support this perspective.

According to Pfizer’s 2021 second-quarter earnings report, receiving an additional booster dose of their Covid-19 vaccine after having had the initial two doses increases the amount of Delta variant antibodies fivefold in 18-to-55-year-olds and 11-fold in 65–85-year-olds.

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