Researchers say they are seeing some waning of protection against Covid infections in double-jabbed people.
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. ทดลองเล่นสล็อต joker
Although some breakthrough infections may be happening, vaccines are still doing a very good job at protecting people against severe Covid illness and deaths.
Public Health England estimates that around 84,600 deaths and 23 million infections have been prevented as a result of the Covid-19 vaccination programme in England so far.
Prof Tim Spector, lead investigator on the Zoe Covid Study app behind the research, said the findings could explain recent breakthrough infections that some fully vaccinated people have been reporting.