Moderna says early evidence suggests its COVID-19 vaccine works against Delta variant and others

An employee worked in the preclinical manufacturing area at the Moderna facility in Norwood.Nancy Lane/Associated Press

Moderna said Tuesday that a small laboratory test suggested its COVID-19 vaccine was effective against worrisome viral variants, including the highly transmissible Delta strain that now accounts for one in five cases in the United States.

The Cambridge biotech said its messenger RNA vaccine produced neutralizing antibodies against seven variants first identified in Angola, India, Nigeria, South Africa, and Uganda. The company tested blood serum drawn from eight vaccinated volunteers a week after they received their second shot and mixed with different variants in a laboratory.

“These new data are encouraging and reinforce our belief that the Moderna COVID-19 Vaccine should remain protective against newly detected variants,” Stéphane Bancel, chief executive of Moderna, said in a statement. “These findings highlight the importance of continuing to vaccinate populations with an effective primary series vaccine.”

According to a copy of the study on a pre-print server and not yet peer reviewed, the variants blunted antibody levels from a minimal to modest degree in vaccinated individuals, but the vaccine still appeared to provide enough protection.

The results are encouraging but don’t necessarily reflect how the vaccine will work against the variants in a real-world setting, in contrast to larger trials involving vaccinated people who have been exposed to variants in their communities.

“We remain committed to studying emerging variants, generating data and sharing it as it becomes available,” Bancel said.

Moderna said it is continuing to test several vaccine booster candidates in clinical trials, should they prove necessary.

The company’s stock closed up 5.2 percent to $234.46.

While promising, Moderna’s announcement wasn’t surprising. A much larger Public Health England study published in May found that two doses of Pfizer’s similar mRNA coronavirus vaccine were 88 percent effective against the Delta variant among people who had received the shots and went about their lives.

Pfizer’s two-shot vaccine was cleared by the Food and Drug Administration on Dec. 11, the first authorized for emergency use in the country. The FDA authorized Moderna’s vaccine a week later as the second that could be deployed.

The agency cleared a third vaccine, a single-dose formulation from Johnson & Johnson, in late February. The vaccine uses different technology than Pfizer’s or Moderna’s. Researchers are also testing how effective the Johnson & Johnson shot is against several variants, including Delta.

The Delta variant is a highly infectious form of the virus that was first detected in India and has been identified in at least 85 countries. Its presence in the United States has doubled in the past two weeks. Dr. Anthony Fauci, the government’s top infectious diseases doctor, has called it “the greatest threat” to eliminating the virus in the United States.

World Health Organization officials emphasized last week the need for fully vaccinated people to “continue to be appropriately cautious” and maintain social-distancing measures like mask wearing as the highly infectious Delta variant becomes increasingly common and fuels new surges globally.

That advice conflicts with recommendations from the Centers for Disease and Control and Prevention, which told fully vaccinated Americans in May that they no longer needed to wear masks indoors or to keep six feet from other people.

Nearly 154 million Americans have been fully vaccinated, including more than 81 million with Pfizer’s vaccine, more than 60 million with Moderna’s, and more than 12 million with Johnson & Johnson’s, according to the CDC.