Covid-19: what if delaying the second dose increased the immune response?

The number of antibodies forming against Covid-19 in response to a vaccine injection is three times higher in older people who received their second dose after twelve weeks instead of three, according to a new study from the University of Birmingham.

Scientists at the University of Birmingham, UK, say in a new study, carried out in collaboration with Public Health England, that in the fight against Covid-19, postponing the second dose of the Pfizer / BioNTech vaccine to 12 weeks instead of three, as recommended by the European Medicines Agency (EMA), is increasing the amount of antibodies in the elderly.

“This is the first time that antibodies and cellular responses have been studied when the second dose of vaccine is given after an extended interval. Our study shows that the maximum antibody responses after the second injection are markedly improved in the elderly with a delay of 12 weeks, ”explains one of the research managers.

The study, carried out on 175 people over 80, compared the immune response to injections three and 12 weeks apart. She found that extending the interval would increase the antibody response. Thus, those who received their second dose 12 weeks after the first have 3.5 times more antibodies than those who received it after only three weeks.

Two injections at spaced intervals …

An important finding for the country since the United Kingdom has chosen to extend the period from three weeks to 12 to allow a higher percentage of the population to receive a dose of vaccine more quickly.

“The higher antibody responses in people receiving two doses of the vaccine 12 weeks apart provide further evidence of the benefits of the UK approach to prioritizing the first dose of vaccine,” said another co-author of study.

In France, the two injections of the Pfizer / BioNTech or Moderna vaccines must be spaced 42 days apart, or approximately six weeks.

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However, this is a pre-publication and the study has not yet been peer-reviewed.

An interval of three weeks between the two injections of the Pfizer / BioNTech vaccine was recommended on January 28, 2021 by the European Medicines Agency (EMA) in the midst of a debate on the possibility of spacing out the doses by six weeks instead of three or four.

… Or just one?

Moreover, British researchers from the University of East Anglia examined the data from the vaccination campaign in Israel with the Pfizer / BioNTech vaccine at the start of the year. They had drawn a conclusion from the beginning of February: a single injection would be enough to provide protection of some 90% in 21 days.

An Israeli vaccination campaign official said in January that a single dose seemed “less effective than we had thought.” Pfizer agreed, estimating the efficacy at 52% after a single dose.

However, British scientists claimed that high protection was formed just before the administration of the second dose, 21 days after the first.

“We found that the efficacy of the vaccine was still virtually zero until about 14 days after vaccination. But then, after day 14, immunity gradually increased day by day to around 90% by day 21, and then did not improve any more, ”one of the study’s authors told The Guardian. .

Any improvement observed was before the second injection, he noted.

“This shows that a single dose of the vaccine is highly protective, even though it can take up to 21 days.”


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