Moderna vaccine less effective against omicron, early data suggests

Two doses of Moderna's mRNA vaccine are less effective against the omicron coronavirus variant, preliminary findings published Dec. 15 in the preprint server MedRxiv suggest. 

For the lab-based study, researchers looked at blood samples from 30 Moderna recipients and found their antibodies were about 50 percent less effective at neutralizing the variant compared to the original strain. 

This "could lead to an increased risk of symptomatic breakthrough infections," the study said. 

However, a booster dose strengthened the antibody response against omicron at levels comparable to the shot's effectiveness against the delta strain. Seven participants received a booster. 

"What these results are telling us is that if omicron becomes a dominant variant, it's going to become even more important that people get their boost," David Montefiori, PhD, a virologist at Durham, N.C.-based Duke University School of Medicine who helped conduct the study, told NPR

Omicron is also more likely to evade the protection of Pfizer-BioNTech's vaccine against infection, preliminary real-world findings from South Africa suggest. Still, the vaccine offered 70 percent protection against hospitalization in fully vaccinated people. The drugmaker on Dec. 8 shared results from a laboratory study that found people who received two doses of the shot saw a 25-fold drop in antibodies against omicron, though a booster dose offered similar neutralization as the two-dose series provided against the original coronavirus strain.


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