Efficacy of Pfizer/BioNTech coronavirus vaccine drops to 84pc after 6 months

The efficacy of the Pfizer/BioNTech coronavirus vaccine fell from 96% to 84% after six months, a new preprint report by medRxiv showed on Wednesday.

"Efficacy peaked at 96.2 percent during the interval from 7 days to <2 months post-dose 2, and declined gradually to 83.7 percent from 4 months post-dose 2 to the data cut-off, an average decline of ~6 percent every 2 months," the report said.

Ongoing follow-up is needed to understand the persistence of the vaccine effect over time, it added.

According to data that has not been reviewed, the vaccine was initially 91% effective at preventing COVID-19 over the course of six months.

The US health-oriented news outlet Stat suggested that if the vaccine efficacy keeps declining at the rate described in the study, it will end up being less than 50% within 18 months from the date of vaccination and so a third dose would be required.