The fight against the coronavirus pandemic in some wealthier countries has become a race between the highly contagious delta variant and the rollout of vaccines most scientists say still provide strong protection.

Researchers are scrambling to confirm that vaccines remain effective in the face of the variant, first identified in India, which has come to account for more than half of new covid-19 cases in the United States, according to the Centers of Disease Control and Prevention.

The confirmed global death count neared 4 million Wednesday, as delta variant cases continued to surge.

Israel’s Health Ministry this week announced that the Pfizer-BioNTech vaccine – one of the world’s most effective shots – was offering only 64% protection against infection and symptomatic illness caused by the delta variant.

But the vaccine remains highly successful at preventing severe illness and death, the ministry said.

Israel has fully inoculated about 60% of its population, the vast majority of whom received the Pfizer-BioNTech vaccine. Some health experts criticized the Israeli study, and warned against overreliance on a single study result, pointing to a number of factors – including testing patterns – that could have influenced the result in ways difficult to measure.

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Nonetheless, a substantial documented drop in the vaccine’s protection level could have serious implications for countries betting almost entirely on mass immunization campaigns – as well as poorer nations that have barely started their own vaccine drives.

In Britain, where the variant accounts for at least 95% of new infections, government officials have admitted that cases will probably soar after remaining pandemic-related restrictions are lifted this month, despite the fact that more than 50% of the population has been fully vaccinated.

England’s chief medical officer has warned of an increase in “long covid,” in which symptoms persist for months, among young people. While Britain’s vaccination rollout is among the world’s fastest, the youth inoculation rate is still relatively low.

Officials maintain that high overall vaccination rates will keep hospitalizations and deaths low. In May, researchers affiliated with Public Health England found that two doses of the Pfizer-BioNTech vaccine were 88% effective against symptomatic illness caused by the delta variant.

“We will soon be able to take a risk-based approach that recognizes the huge benefits that the vaccines provide both to people who get the jab and their loved ones too,” British Health and Social Care Secretary Sajid Javid said Tuesday.

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His opposition counterpart, Jonathan Ashworth, however, expressed fear that the vaccine wall the government was relying on to protect the country was “only half built.”

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The Washington Post’s Katerina Ang in Singapore contributed to this report.