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. Israel’s Health Ministry this week announced that the Pfizer-BioNTech vaccine — one of the world’s most effective shots — was offering only 64 percent 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.

Here are some significant developments:

  • Sydney’s lockdown has been extended by a week to July 16, New South Wales state officials confirmed. Australia’s largest city is struggling to stamp out a small outbreak of the delta variant, but only about 8 percent of the country has been fully inoculated.
  • Singapore will not include people inoculated with the Sinovac shot in its national vaccine count. The city-state has not approved the Chinese-developed shot for its vaccination program, though some private clinics are allowed to administer Sinovac doses.
  • The United States is dispatching 2 million Moderna vaccine doses to Vietnam, the White House said. The Southeast Asian country had been a coronavirus containment success, but its vaccination rollout has been slow, and a wave of infections starting in May has not receded.
  • Turkmenistan is making coronavirus vaccination mandatory for all adults, Reuters reported Wednesday, citing the Central Asian nation’s Health Ministry. The authoritarian government has reported no coronavirus cases since the pandemic began, but this year registered Russian- and Chinese-made vaccines for use inside the country.
  • England’s chief medical officer 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; the country is jettisoning almost all distancing curbs later this month.

Israel has fully inoculated about 60 percent 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.

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 percent 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 percent of the population has been fully vaccinated.

Officials maintain that high 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 percent 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.

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.”

Katerina Ang in Singapore contributed to this report.