Moderna Vaccine Efficacy Takes a Hit From Omicron

Two doses of Moderna’s COVID-19 vaccine appear to be ineffective at neutralizing the Omicron variant, increasing the risk of breakthrough infections. A booster dose, however, restores antibodies to protective levels, according to a preliminary study shared publicly on Wednesday.

Researchers from Duke University and the National Institutes of Health created a “pseudovirus”—a virus engineered in a lab to mimic the mutations found in the Omicron variant. The Omicron pseudovirus infected blood samples from 30 people who had received two Moderna shots.

Antibodies in these samples were at least 50 times less effective at neutralizing Omicron.

But booster shots seem to help. An additional 17 participants had received a third shot of the Moderna vaccine. The antibodies in their blood were about as effective at blocking Omicron as they were at protecting against Delta.

The findings have not yet been reviewed by other scientists.

Recent research also indicated that two doses of Pfizer’s COVID-19 vaccine showed a 25-fold drop in antibodies against against Omicron. A third dose of the vaccine appeared to boost antibodies up to a protective level.

When the Omicron variant first emerged, vaccine manufacturers had prepared to create an Omicron-specific vaccine. During a White House press briefing on Wednesday, Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, said a reformulated vaccine isn’t necessary at this time. He cited data including research from the Vaccine Research Center, which would be shared publicly in coming days.

“The message remains clear: If you are unvaccinated, get vaccinated. And particularly in the arena of Omicron, if you are fully vaccinated, get your booster shot,” Fauci said.

Omicron now accounts for nearly 3% of the COVID-19 cases in the United States, according to the CDC’s latest estimates. That’s about a seven-fold jump from last week. In a region including New York and New Jersey, the variant accounts for about 13% of the samples.

Early data suggests that Omicron has a doubling time of two days, which means it's more transmissible than Delta, according to CDC Director Rochelle Walensky. According to a recent study, Delta cases reported in the United Kingdom were doubling roughly every 11 days.

"It means that it is vital for everyone to get vaccinated and boosted if they are eligible," Walensky said at a White House briefing. "Given the increase in transmissibility, this also means continuing to be vigilant about masking in public indoor settings, in areas of substantial or high community transmission.  And as of now, this represents about 90% of all counties in the United States."

As many Americans plan to gather or travel for winter holiday celebrations, other COVID-19 mitigation efforts will remain important. In addition to getting vaccinated and booster, Walensky said, having good ventilation, social distancing, and hand washing "continue to hold and continue to serve us very well in preventing disease."