After the initial two doses of Covishield coronavirus vaccine, there should be a third dose preferably six months after the second shot, Serum Institute of India CEO Adar Poonawalla said. "After six months, the antibodies go down and that is why I have taken the third dose. We have given the third dose to our seven to eight thousand SII employees. For those who have completed the second dose, it is my request to take a booster dose third dose after six months," he said, reports said, quoting a press conference he attended.
Earlier, a study had claimed that the total antibody levels start to wane six weeks after complete immunisation with Pfizer and AstraZeneca vaccines, and can reduce by more than 50 per cent over 10 weeks, according to study published in The Lancet journal. The researchers from University College London (UCL) in the UK noted that if the antibody levels carry on dropping at this rate, there are concerns that the protective effects of the vaccines may also begin to wear off, particularly against new variants. However, they said, how soon that might happen cannot be predicted yet.
Antibody levels were also much higher in vaccinated people than those with prior SARS-CoV-2 infection, they said.
For Pfizer, antibody levels reduced from a median of 7506 Units per millilitre (U/mL) at 2141 days, to 3320 U/mL at 70 or more days. For AstraZeneca vaccine, antibody levels reduced from a median of 1201 U/mL at 020 days to 190 U/mL at 70 or more days, over five-fold reduction.
-Inputs from PTI
