TEL AVIV—Data from Israel suggests Pfizer Inc.’s vaccine is less effective at protecting against infections caused by the Delta variant of Covid-19 but retains its potency to prevent severe illness from the highly contagious strain.
The vaccine protected 64% of inoculated people from infection during an outbreak of the Delta variant, down from 94% before, according to Israel’s Health Ministry. It was 94% effective at preventing severe illness in the same period, compared with 97% before, the ministry said.
An Israeli official said Tuesday the health ministry findings released a day earlier were preliminary and based on data collected from June 6 through early July. The ministry didn’t release its methodology or the data on which its findings were based.
A spokesman for Pfizer said he couldn’t comment on an unpublished survey, but pointed to a recent study that showed the vaccine continued to offer protection against new variants.
The findings came as new cases of Covid-19 in Israel rose to a seven-day average of 300 on Tuesday from around 10 a day for most of last month. To prevent another surge in infections, the government late last month reimposed an indoor mask requirement and other measures after finding that about 90% of the new infections were likely caused by the Delta variant. Israel’s total population is around 9.3 million.