Getting vaccinated against COVID-19 is still known to be the best method of protection against the virus. It is thought in just one year almost 20 million deaths were avoided worldwide thanks to the jab. But a new study has found having vaccines too soon after each other could reduce their efficacy.
But he stressed that getting repeat vaccinations was still important.
“It is important to clarify that having antibodies and getting boosted is a good thing, so anyone who is due their booster shot should do so,” he said. “We don’t want people to think otherwise.
“The study just pinpoints potential strategies by which next-generation vaccines could be tweaked to improve their efficacy, for example, by developing vaccines that bypass pre-existing antibodies.”
As part of the study, which was published in Cell Reports journal, the team studied a cohort of 85 people who had been vaccinated with the Moderna or Pfizer-BioNTech vaccines.
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Scientists discovered that lower antibody levels before a booster were associated with a higher-fold increase in antibody levels after the booster.
“This suggests that pre-existing antibodies induced by prior vaccinations may negatively affect the level of responses induced by mRNA booster vaccines,” Mr Penaloza-MacMaster said.
The team’s subsequent studies in mice showed that antibodies generated by prior vaccinations accelerated the clearance of the vaccine from the body, limiting the amount of vaccine available to trigger new immune responses after the booster shot.
Mr Penaloza-MacMaster said: “In other words, the antibody responses generated after prior vaccinations rapidly wipe out the vaccine during a subsequent booster shot, limiting the immune response that can be generated by the booster shot.”
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This was not caused by competition between antibodies and B cells for the vaccine antigen but appears to be the result of so-called “antibody effector mechanisms”, which clear foreign substances from the body.
In the experiments in mice, scientists found the updated Omicron vaccines are superior to the original vaccines at clearing the Omicron infection, if the animal’s immune system has never “seen” the original SARS-CoV-2 via vaccination before.
But the relative superiority of an Omicron vaccine is more limited if the animal has already had the original vaccine.
Why increasing time between vaccinations is important
It was concluded that increasing time between each vaccination could boost the immune system’s response.
“We showed in prior studies – as did other labs – that the longer the interval between vaccinations, the better the response,” Mr Penaloza-MacMaster said.
“It’s better to wait six months than two weeks before you boost, but the reasons for this were not clear. We have thought this could be simply due to the time-dependent maturation of the immune response.
“But another reason is that waning of antibodies would allow the booster to persist in the body for a longer time. If the booster shot in your muscle perdures for a longer time, you are likely to develop robust immune responses.”
He added: “What excites me about this study is what we can learn in terms of how to make better booster vaccines.”
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