The seven jabs used as boosters against COVID-19 mostly produced a strong immune response, though results varied depending on the vaccine combination, a study confirm on Friday.
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Researchers in the UK last June, looked at about 3,000 people to compare various combinations of vaccines and their effects after a third dose.
Some patients in the study, published in the leading medical journal The Lancet, had been fully vaccinated either with AstraZeneca or Pfizer/BioNTech.
At least two months after the second dose of Pfizer and three months for AstraZeneca, they received a third jab either of those two shots or CureVac, Moderna, Novavax, Valneva, or Janssen.
Other participants received a placebo.
In nearly all patients except for those who received a placebo, participants produced an increased antibody response – except for the initial vaccination by Pfizer followed by a Valneva booster, which showed no noticeable difference.
“All of the vaccines that boosted immunity did so in older and younger people; however, there were marked differences in response between specific booster vaccines, consistent with other data from non-randomised studies,” the study said.
There were several limits to the study.
The third doses were administered soon after the second dose — sometimes less time elapsed between the second and third doses than between the first and second ones, which could have reduced immunity.
But even more importantly, the study measured subjects’ immune responses but did not test their real efficacy against COVID-19 infection or severity of illness
Follow-up on the subjects will look at their immunity levels between seven and eight months after their first doses, with results expected next year.
The study also looked at side effects, which it said varied in intensity but were deemed acceptable regardless of the combination.
Study confirms that Covid-19 vaccines can boost immunity