(The Hill) – A preprint study published Wednesday indicated that the antibodies in blood samples from recipients of two Moderna doses were less effective at neutralizing the omicron variant, suggesting an increased risk of symptomatic breakthrough cases. 

The preliminary research, which has not yet been peer-reviewed, analyzed blood samples from 30 participants fully vaccinated with two Moderna doses. Researchers tested antibodies in the blood with “pseudovirus” versions of the omicron strain at National Institutes of Health and Duke University laboratories.

They found these antibodies in two-dose Moderna recipients were at least 50 times less effective at neutralizing the omicron strain, which “could lead to an increased risk of symptomatic breakthrough infections.”

But the seven participants who received a Moderna booster saw an about 12-fold improvement in the neutralization against the omicron variant, which researchers noted “may substantially reduce the risk” of COVID-19.

Data from South Africa also found that two doses of the Pfizer-BioNTech vaccine were only 33 percent effective at preventing omicron infection, although it was still 70 percent effective against hospitalization. 

Top infectious disease expert Anthony Fauci cited the preliminary data on the effectiveness of mRNA boosters when saying there’s no need for a vaccine designed specifically to combat the omicron variant yet.

“Our booster vaccine regimens work against omicron,” Fauci said at a Wednesday briefing. “At this point there is no need for a variant-specific booster.”

Slightly more than a quarter of the U.S. population has received their booster dose, according to Centers for Disease Control and Prevention (CDC) data.

Fauci said the Moderna preprint study on the Moderna vaccine will be published in a preprint server “next week.”

Scientists raised concerns about the omicron variant first reported in South Africa and Botswana in late November due to its high number of mutations, and early data indicates it’s more transmissible than the delta variant and doubling every two days.

At least 36 states and 75 countries have identified omicron cases. The CDC estimates that the strain makes up 3 percent of cases in the U.S., with higher rates in areas like New York and New Jersey.

“Looking at early data on transmissibility of omicron from other countries, we expect to see the proportion of omicron cases here in the United States continue to grow in the coming weeks,” CDC Director Rochelle Walensky said at a briefing.