Dr Walid Gellad,a professor at University of Pittsburgh’s medical school,said there seems to be a benefit of having the third dose in the Delta wave for symptomatic COVID-19.
“I’m just still very curious if this is primarily in people who are much,much older. Because what we don’t want to do is run out and give boosters to 25-year-olds who had COVID before and got two doses of the vaccine,just based on this press release,” Gellad said.
Pfizer had said its two-shot vaccine’s efficacy drops over time,citing a study that showed 84 per cent effectiveness from a peak of 96 per cent four months after a second dose. Some countries had already gone ahead with plans to give booster doses.
The trial results come a day after the US Food and Drug Administration authorised booster doses of the COVID-19 vaccines from Moderna and Johnson&Johnson,and said Americans could choose a different shot from their original inoculation as a booster.
The agency previously authorised boosters of the Pfizer/BioNTech shot at least six months after the first round of shots to increase protection for people aged 65 and older,those at risk of severe disease and those who are exposed to the virus through their work.
The drugmakers said on Thursday,local time,the median time between the second dose and the booster shot or the placebo in the study was around 11 months,adding there were only five cases of COVID-19 in the booster group,compared with 109 cases in the group which received the placebo shot.