Moderna says neutralizing antibodies generated by its COVID-19 vaccine against three variants of the virus that causes the disease waned substantially 6 months after the second dose.
Because of this, the company expects an increase in breakthrough infections with a need for boosters before winter.
In an experiment, a 50-mg dose of the vaccine, given as a third shot, boosted levels of antibodies in 20 previously vaccinated people by 32 times against the Beta variant, by 44 times against the Gamma variant, and by 42 times against Delta.
The new data was presented in an earnings call to investors and is based on a small study that hasn’t yet been published in medical literature.
The company also said its vaccine remained highly effective at preventing severe COVID outcomes through 6 months.
Last week, Pfizer released early data suggesting a similar drop in protection from its vaccine. The company also showed a third dose substantially boosted protection, including against the Delta variant.
The new results come just 1 day after the World Health Organization implored wealthy nations to hold off on third doses until more of the world’s population could get a first dose.
More than 80% of the 4 billion vaccine doses given around the world have been distributed to high-income countries.
A version of this article first appeared on WebMD.com.