Moderna Vaccine Efficacy Takes a Hit From Omicron

COVID variants.

Eugene Mymrin / Getty Images

UPDATE: Moderna Announces Booster Findings

A booster shot of Moderna’s COVID-19 vaccine increases the level of antibodies that can protect against Omicron, the company said in a December 20th statement.

The currently authorized booster dose of 50 micrograms boosted virus-fighting antibody levels 37-fold against Omicron. A full 100-microgram dose of the same vaccine—the same dose given in the primary immunization—stimulated an 83-fold increase in antibody levels.

Researchers sampled blood from 20 booster recipients who received a 100-microgram booster and 20 who were boosted with a 50-microgram dose. They infected these samples with an Omicron pseudovirus and measured the resulting neutralizing antibody levels.

In the statement, Moderna Chief Executive Officer Stéphane Bancel said the company will continue developing an Omicron-specific booster candidate, in case it’s needed in the future. The company expects the new formulation will be tested in clinical trials early next year.

In the meantime, Moderna said that given the rapid spread of Omicron and the promising data on booster effectiveness, the company “will focus its near-term efforts to address Omicron on the mRNA-1273 booster."

Key Takeaways

  • Omicron diminishes the level of neutralizing anitbodies about 50-fold in people who received two doses of Moderna’s COVID-19 vaccine, per a preliminary lab study.
  • A booster shot of the mRNA vaccine appears to restore protective antibody levels.
  • Health officials say an Omicron-specific vaccine is not necessary at this time, citing the benefits of boosters.

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."

What This Means For You

Vaccination remains the best way to protect yourself and others from infection by Omicron, Delta, and the other COVID-19 variants. A booster of mRNA vaccine appears to be effective at preventing severe outcomes from Omicron. You can find locations to receive a vaccination and booster shot at

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Montefiori DC, Doria-Rose N, Shen X, et al. Booster of mRNA-1273 Vaccine Reduces SARS-CoV-2 Omicron Escape from Neutralizing Antibodies. medRxiv. December 15, 2021. DOI: 10.1101/2021.12.15.21267805.

  2. Centers for Disease Control and Prevention. COVID Data Tracker.

  3. Centers for Disease Control and Prevention. COVID Data Tracker.

  4. Tanne JH. Covid 19: US cases rise amid omicron fears but booster shots offer protection, experts say. BMJ. Published online December 16, 2021:n3098. doi. 10.1136/bmj.n3098. 

  5. Riley, S; Wang, H; Eales, O; Haw, D; Walters, C, et al. REACT-1 round 12 report: resurgence of SARS-CoV-2 infections in England associated with increased frequency of the Delta variant. Imperial College London. Published June 17, 2021.