The real-world study includes data on positive Covid PCR test results between May and July 2021 among more than a million people who had received two doses of Pfizer or AstraZeneca vaccine. 

Protection after two shots of Pfizer decreased from 88% at one month to 74% at five to six months.

For AstraZeneca, the fall was from 77% to 67% at four to five months.

Waning protection is to be expected, say experts, reports BBC.

Although some breakthrough infections may be happening, vaccines are still doing a very good job at protecting people against severe Covid illness and deaths.