LONDON— Protection against COVID-19 offered by 2 doses of the Pfizer/BioNTech and the Oxford/AstraZeneca coronavirus vaccines begins to fade within 6 months, underscoring the need for booster shots, according to researchers in Britain.
After 5 to 6 months, the effectiveness of the Pfizer jab at preventing COVID-19 infection in the month after the second dose fell from 88 percent to 74 percent, an analysis of data collected in Britain's ZOE COVID study showed.
For the AstraZeneca vaccine, effectiveness fell from 77 percent to 67 percent after 4 to 5 months.
The study was based on data from more than 1.2 million test results.
Previous analysis of data has suggested that vaccines provide protection for at least 6 months.
Under a worst-case scenario, protection could fall below 50 percent for older people and health care workers by the winter, Tim Spector, principal investigator for the ZOE COVID study, said.
"It's bringing into focus this need for some action. We can't just sit by and see the protectiveness slowly waning while cases are still high and the chance of infection still high as well," Spector told BBC television.
Britain is starting to plan for a COVID-19 vaccine booster campaign later this year after top vaccine advisers said it might be necessary to give third shots to the elderly and most vulnerable from September.