Moderna on Wednesday released preliminary data on its omicron-specific coronavirus vaccine, calling it the company's "lead candidate" to serve as a booster shot this fall—but it is still unclear how effective the shot will be against the current subvariant strains spreading in the United States.

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Moderna releases preliminary data on its omicron-specific vaccine

Moderna's omicron-specific booster, called mRNA1273.214, is a bivalent vaccine, which means that it contains a combination of the mRNA coding of the spike protein from the original strain of the coronavirus and the omicron variant. 

The clinical trial involved 814 volunteers with an average age of 57 vaccinated with three doses of Moderna's existing vaccine. Of the volunteers who had no signs of prior coronavirus infection, the researchers found that their new vaccine combination produced 1.75 times the amount of antibodies against omicron than the current Moderna vaccine did alone.

Paul Burton, Moderna's CMO, described the results as highly encouraging, but also noted that a less than twofold increase in neutralizing antibodies over the existing vaccine is "only a modest benefit."

"Does that justify switching vaccine composition given the cost and the logistics and everything else that involved?" he asked. "That's what the argument is going to be about."

The company said it plans to submit the preliminary data to FDA in the coming weeks, with hopes that the new booster will be available later this summer, STAT News reports.

In recent months, FDA has held public hearings on how to choose which strains of the coronavirus should be included in this fall's booster shots and who should be eligible to receive them. On June 28, the agency will hold another meeting on this topic, and vaccine makers have cautioned that decisions will need to be made soon for the vaccines to be widely available this fall, STAT News reports.

Will it be effective against other subvariants?

While Moderna's updated vaccine provides increased protection against the omicron variant, new subvariants have been emerging for months now—and some vaccine experts have highlighted the importance of a booster that can protect against the latest subvariants, BA.4 and BA.5, the New York Times reports.

The BA.2 and BA.2.12.1 omicron subvariants are dominant, but BA.4 and BA.5 currently account for 13% of new cases in the United States and are spreading quickly. In fact, some estimates project that they could become the dominant strains in the United States within a month.

Currently, Moderna has not released any data on how well the updated vaccine protects against BA.4 or BA.5. According to Stephen Hoge, Moderna's president, the company's researchers are still gathering data on those and other subvariants.

Hoge noted that a small sample, combined with other studies, suggested that the updated vaccine produced two to threefold lower levels of neutralizing antibodies against the BA.4 and BA.5 subvariants than against omicron. In addition, Moderna's researchers have not determined whether the updated vaccine will provide more lasting protection than the current one.

However, Burton said, "We really feel like this is a sort of fundamental turning point in our fight against this virus — that we can adapt to a variant … It works." (LaFraniere, New York Times, 6/8; Herper, STAT News, 6/8; Abutaleb/Jeong, Washington Post, 6/8)