Two Moderna doses provide substantially low neutralizing effect against Omicron -U.S. NIAID

There was no need yet for a variant-specific booster shot, he added. Early data suggests Omicron is more transmissible than the Delta variant of the virus, U.S. Centers for Disease Control and Prevention Director Rochelle Walensky said at the same briefing, adding that Omicron appeared to have "a doubling time of about two days".

The neutralizing activity of two doses of Moderna's COVID-19 vaccine is "substantially low" against the Omicron variant of the coronavirus, National Institute of Allergy and Infectious Diseases (NIAID) Director Anthony Fauci said on Wednesday, citing NIAID data.

However, a third, booster dose of the Moderna vaccine puts the neutralizing activity "well within the range of neutralizing Omicron," Fauci told reporters at a White House briefing. There was no need yet for a variant-specific booster shot, he added.

Early data suggests Omicron is more transmissible than the Delta variant of the virus, U.S. Centers for Disease Control and Prevention Director Rochelle Walensky said at the same briefing, adding that Omicron appeared to have "a doubling time of about two days". There are confirmed cases of the variant in at least 36 states, and health officials expect to see the proportion of cases in the United States to continue growing over the coming weeks, she said.

Walensky said officials were starting to see COVID-19 cases increase in fully vaccinated nursing-home residents, but residents who have had a booster shot have an infection rate that is 10 times lower.