Booster doses in the COVID vaccine can dramatically increase the body’s immune defenses, according to a study that has raised hope that the omicron variant will not bring another wave of serious illness.
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Developed by UK researchers and published in the medical journal The Lancet, the Cov-Boost trial has measured the immune response of nearly 3,000 people. Two to three months after the second dose of the AstraZeneca or Pfizer COVID-19 vaccine, one group was given one of seven possible booster doses and the other a placebo.
Those who received the third dose of Pfizer after two doses of AstraZeneca had developed an antibody level almost 25 times higher one month later than those who received the placebo. For those who received the Pfizer booster after two doses of Pfizer, their antibody level increased eightfold.
In the study, the strongest effect was achieved by giving a full dose of Moderna vaccine as a booster (only half a dose of Moderna is now given in the approved booster program in the EU, US and UK). For the group that had previously received two doses of AstraZeneca, the full dose of Moderna had a 32-fold increase in antibody levels. In the group that had been vaccinated with Pfizer, the dose of Moderna multiplied by 11 the level of antibodies.
The results show that the mRNA technology vaccines developed by Moderna and Pfizer are very effective as a booster, but the scientists say it is necessary to collate results, since the people who participated in the trial started with different antibody levels. A few months after getting vaccinated with Pfizer, for example, antibody levels tend to stay high, and a booster can’t raise them much higher.
According to Professor Saul Faust, head of the trial and director of the NIHR clinical research center at the University Hospital Southampton NHS Foundation Trust, “these are remarkably effective immune boosters, far in excess of what is needed to prevent hospitalization and death.” . Although there were several side effects from the booster (among those who reported them, a majority reported fatigue, headache, or arm pain), the study found no safety concerns.
T cells
In addition to the antibodies, the scientists analyzed the effect that the extra doses had on T cells, a key component of the immune system directly related to preventing serious disease progression. Most of the boosters, including those from Pfizer, Moderna and AstraZeneca, increased T-cell levels, regardless of the vaccine given in the first two doses.
One result the scientists highlighted is that the T-cell response to the worrisome beta and delta variants was just as good as to the virus originally detected in Wuhan. “Our hope as scientists is that protection against hospitalization and against death remains intact,” Faust said regarding the importance of this finding for omicron behavior.
Professor of molecular virology at the University of Nottingham Jonathan Ball, who was not involved in the study, shares Faust’s optimism. “While there were variants like delta that reduced the overall effect of antibodies to kill the virus, the T-cell response was never affected,” he says. “The fact that the mRNA booster has given a remarkable increase in both antibodies and T cells is great news, especially now, when all our attention is focused on the appearance of the omicron variant.”
“We still do not know how this increased immunity translates, especially in protection against serious evolutions of the disease, but I remain convinced that our vaccines will continue to provide the protection we need,” he adds.
The first results of the Cov-Boost study support the decision of the UK vaccination committee to shorten the waiting period before receiving the booster dose, from six to three months. The European Center for Disease Prevention and Control currently maintains its recommendation to receive the additional dose at six months.
The study also demonstrates the efficacy of the third dose with AstraZeneca: it increases the level of antibodies three times for those vaccinated with AstraZeneca; and five times for those vaccinated with Pfizer.
Another result of the study suggests that the booster programs could be converted to a half dose of Pfizer without losing too much protection. The data shows that the half dose of Pfizer multiplies by 17 the antibody level for those vaccinated with AstraZeneca, and by more than six for those vaccinated with Pfizer.
Translated by Francisco de Zárate
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