Protection against Covid-19 offered by two doses of the Pfizer/BioNTech and the Oxford/AstraZeneca coronavirus vaccines begins to fade within six months, underscoring the need for booster shots, according to researchers in Britain.

After five to six 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...