World Health Organization (WHO) officials stressed Friday the need for fully vaccinated people to “continue to be appropriately cautious” and keep up with social distancing measures like mask wearing as the highly infectious Delta variant of the coronavirus becomes increasingly dominant in the U.S. and spurs new Covid-19 surges around the world—including in highly vaccinated countries.

Key Facts

• The Delta variant, which was first identified in India and is more infectious than previous coronavirus strains, is now responsible for approximately 10% of coronavirus infections in the U.S. as of June 5 and has caused new Covid-19 outbreaks in such countries as the United Kingdom, Australia and Israel.
• The variant’s spread means people should follow public health measures like mask wearing, frequent sanitizing and social distancing “with much more care,” Dr. Michael Ryan, executive director of the WHO’s World Emergencies Programme, said at a press briefing Friday, saying the Delta strain should make the world “more cautious, more diligent, and more dedicated to” following those protocols.
• WHO senior advisor Dr. Bruce Aylward said fully vaccinated people should “play it safe,” noting people can “end up as part of a transmission chain” even if they’ve received both shots.
• Dr. Maria Van Kerkhove, the WHO technical lead on Covid-19, said while vaccines are “incredibly effective at preventing severe disease and death” including against the Delta variant, the strain is a “dangerous variant” and large events taking place as the variant spreads “will have consequences.”
• “Us[ing] masks consistently” and following other social distancing measures like avoiding crowds, hand washing and being in well-ventilated spaces is “extremely important, even if you’re vaccinated,” Dr. Mariangela Simao, WHO assistant director-general for access to medicines and health products, said, warning, “Vaccine alone won’t stop the community transmission.”

Crucial Quote

“The first message that we want to be careful about is saying once you’re vaccinated, you can go ahead and do whatever. Yes, you can reduce some measures…but there’s still the need for caution,” Aylward said Friday. “We’re still in a world with a lot of people who are not protected.”

Key Background

Covid-19 vaccines are considered to be largely protective against the Delta variant, with recent studies finding the Pfizer vaccine is approximately 90% effective against the new strain. Only receiving one dose of the vaccine provides far less protection against the variant, however—one Pfizer dose is only approximately 36% effective against symptomatic disease, Public Health England reported—and breakthrough infections are possible but rare. The rise of new and more dangerous variants has provoked fears the virus will continue to mutate and could evolve to evade vaccines, particularly as much of the world remains unvaccinated. While right now measures like vaccines, social distancing and mask wearing have been proven to work against Covid-19, Van Kerkhove said Friday, “there may be a time when this virus evolves, and these countermeasures don’t.”

What to Watch For

The Centers for Disease Control and Prevention has not yet responded to a request for comment on the WHO officials’ warning Friday and whether the agency will reconsider guidance saying fully vaccinated Americans do not have to wear masks in light of the Delta variant’s spread. The Delta strain is right now estimated to double in prevalence approximately every two weeks in the U.S., and it is expected to ultimately become the country’s dominant strain. Dr. Anthony Fauci has warned the variant poses the “greatest threat” to the U.S.’s effort to eradicate Covid-19, and officials have particularly warned about surges in areas where the vaccination rate remains low, such as Southern states like Mississippi and Alabama.

Surprising Fact

Many of the countries that have faced the largest Covid-19 surges in recent months are also those with among the highest vaccination rates in the world—such as Uruguay, Bahrain, the Maldives and the Seychelles—a trend that’s been partially attributed to countries relaxing their restrictions too quickly. The latest highly vaccinated country to face a new surge is Israel, which is reimposing their indoor mask mandate amid a new rise in cases linked to the Delta variant. Approximately half of the country’s new infections appear to be in people who are fully vaccinated with the Pfizer/BioNTech vaccine.