among people already vaccinated for COVID-19, according to first results released May 5.
Furthermore, data from the company’s ongoing phase 2 study show the variant-specific booster, known as mRNA-1273.351, achieved higher antibody titers against the B.1.351 variant than did a booster with the original Moderna vaccine.
“We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants. The strong and rapid boost in titers to levels above primary vaccination also clearly demonstrates the ability of mRNA-1273 to induce immune memory,” Stéphane Bancel, chief executive officer of Moderna, said in a statement.
The phase 2 study researchers also are evaluating a multivariant booster that is a 50/50 mix of mRNA-1273.351 and mRNA-1273, the initial vaccine given Food and Drug Administration emergency use authorization, in a single vial.
Unlike the two-dose regimen with the original vaccine, the boosters are administered as a single dose immunization.
The trial participants received a booster 6-8 months after primary vaccination. Titers to the wild-type SARS-CoV-2 virus remained high and detectable in 37 out of 40 participants. However, prior to the booster, titers against the two variants of concern, B.1.351 and P.1, were lower, with about half of participants showing undetectable levels.
In contrast, 2 weeks after a booster with the original vaccine or the B.1.351 strain-specific product, pseudovirus neutralizing titers were boosted in all participants and all variants tested.
“Following [the] boost, geometric mean titers against the wild-type, B.1.351, and P.1 variants increased to levels similar to or higher than the previously reported peak titers against the ancestral (D614G) strain following primary vaccination,” the company stated.
Both mRNA-1273.351 and mRNA-1273 booster doses were generally well tolerated, the company reported. Safety and tolerability were generally comparable to those reported after the second dose of the original vaccine. Most adverse events were mild to moderate, with injection site pain most common in both groups. Participants also reported fatigue, headache, myalgia, and arthralgia.
The company plans to release data shortly on the booster efficacy at additional time points beyond 2 weeks for mRNA-1273.351, a lower-dose booster with mRNA-1272/351, as well as data on the multivariant mRNA vaccine booster.
In addition to the company’s phase 2 study, the National Institute of Allergy and Infectious Diseases is conducting a separate phase 1 study of mRNA-1273.351.
A version of this article first appeared on Medscape.com.