Do you need a COVID-19 booster vaccine to prevent delta variant?

People who are fully vaccinated against COVID-19 in the U.S. are strongly protected against the highly transmissible delta variant of the coronavirus, and do not need booster shots yet, according to experts. 

"Americans who have been fully vaccinated do not need a booster shot at this time," according to a joint statement from the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA). "We continue to review any new data as it becomes available and will keep the public informed."

The statement came after Pfizer-BioNTech announced plans to seek authorization for a booster shot for its COVID-19 vaccine. Though all the vaccine manufacturers have been studying booster shots just in case they would be needed, Pfizer's decision to seek authorization so soon took experts by surprise, and many of them criticized the announcement, The New York Times reported.

Related: Quick guide: COVID-19 vaccines in use and how they work 

Current evidence suggests the Pfizer, Moderna and Johnson & Johnson's COVID-19 vaccines — the three that are being administered in the U.S. — are all strongly protective against the delta variant, according to the Times. The European Medicines Agency (the European counterpart to the FDA) said it was too early to tell whether more than two shots of COVID-19 vaccines will be necessary, according to Reuters. 

The delta variant, or B.1.617.2, was first identified in India in October 2020 and the World Health Organization designated it a "variant of concern" in May 2021, Live Science previously reported. The delta variant is thought to be 60% more transmissible than the alpha variant, the previous dominant variant in the U.S., according to the report. 

The delta variant currently makes up nearly 58% of new cases in the U.S., according to the CDC.

A study conducted by Public Health England found that Pfizer's COVID-19 vaccine was 88% effective against symptomatic disease caused by the delta variant, Live Science reported. Other studies from Scotland and Canada also found that the vaccine was 79% and 87% effective, respectively, at preventing symptomatic disease from that variant, according to the Times.

But a preliminary study conducted in Israel, which hasn't yet been peer-reviewed, found that the vaccine was only about 64% effective in preventing symptomatic illness but 93% effective in preventing serious illness from delta, according to a statement. Pfizer said its own findings from Israel were similar to these results, according to the Times.

Related: Coronavirus variants: Here's how the SARS-CoV-2 mutants stack up

Johnson & Johnson recently said that its single-shot COVID-19 vaccine was also protective against the delta variant, Live Science previously reported. Moderna has also said that blood sample tests from vaccinated people have shown the delta variant was highly effective in producing antibodies against the delta variant, according to the Times.

Experts say that the vast majority of people who develop severe COVID-19 disease are not vaccinated. 

"Preliminary data from several states over the last few months suggest that 99.5% of deaths from COVID-19 in the United States were in unvaccinated people," Rochelle Walensky, CDC director, said on July 8 during a press briefing. "Those deaths were preventable with a simple, safe shot."

Because the vaccines seem to protect people against catching the delta variant, and especially from developing severe disease and death from it, boosters aren't needed at this time, experts told Buzzfeed News. "The dam is still holding, even if there has been some splashing going on," immunologist E. John Wherry, director of the Penn Institute of Immunology told Buzzfeed News.

"We are prepared for booster doses if and when the science demonstrates that they are needed," the CDC and FDA statement said. 

Originally published on Live Science.