Third dose can boost immunity

Seven jabs used as boosters against Covid-19 mostly produced a strong immune response, though results varied depending on the vaccine combination, a study said yesterday.

Last June researchers in the UK looked at about 3,000 people to compare various combinations of jabs and their effects after a third dose.

Patients in the study, published in 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 -- with the exception of 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.