Moderna says its vaccine’s protection does not wane after six months.

Moderna says its vaccine’s protection does not wane after six months.


The powerful protection offered by Moderna’s Covid vaccine does not wane in the first six months after the second dose, according to a statement with few scientific details that the company released on Thursday morning in advance of its earnings call.

The results may provide comfort to the 63 million Americans who have received two doses of the Moderna vaccine, especially as the super-contagious Delta variant continues to spread across the country.

The news may also inform the global debate about when — or whether — vaccinated people may need a booster shot. Germany, Israel, France and Britain have all decided to administer additional shots to vulnerable populations — such as older people or people with compromised immune systems or both — to bolster their immunity in the face of a Delta-variant-driven surge in cases. The Biden administration is considering a similar strategy.

On Wednesday, the World Health Organization called for a three-month moratorium on boosters. The group urged health leaders to focus instead on vaccinating 10 percent of people in all countries.

Moderna’s data came from a new analysis of its clinical trial, which started in late July 2020 and recruited a total of 30,000 volunteers. In November, the company announced that the vaccine had an impressive efficacy of 94.1 percent. That number didn’t change much after six months, the company reported.

“We are pleased that our Covid-19 vaccine is showing durable efficacy of 93 percent through six months, but recognize that the Delta variant is a significant new threat so we must remain vigilant,” Stéphane Bancel, the chief executive officer of Moderna, said in the statement.

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The announcement lacked important information, such as how recently the study ended. It’s not clear whether it extended into recent months when the Delta variant became dominant.

In June, Moderna released details on an experiment in which its researchers tested antibodies from people who received their vaccine against the Delta variant. They found that the antibodies were moderately less effective at blocking the variant from infecting cells.

Last week, Pfizer and BioNTech released a detailed report of their own mRNA vaccine’s durability after six months. The companies estimated that the vaccine’s efficacy started off at 96.2 percent for the first two months after the second dose. It then declined after that, to 83.7 percent by six months.

But experts cautioned that the calculated decline in the Pfizer-BioNTech study could have been a statistical artifact. Chance alone could lead to a different efficacy estimate at different times. “I would not assume waning immunity based on this study alone,” said Maria Deloria Knoll, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

The F.D.A. is expected to give full approval to the Pfizer-BioNTech vaccine next month. Moderna filed for final approval of its vaccine on June 1, and expects to complete its submission in August.

Moderna said in its statement that in lab experiments of human blood cells, booster shots increased the number of coronavirus antibodies, suggesting that if its vaccine does lose protection in future months, a booster would shore up protection. The company’s clinical trials have also shown robust antibody responses after booster shots.

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In an earnings call last week, Pfizer said that its booster raised antibodies above their original level. Both studies have yet to be published in a scientific journal.