Moderna Inc. (MRNA.O) said on Monday that a booster dose of its COVID-19 vaccine appeared to be protective against the fast-spreading Omicron variant in laboratory testing and that the current version of the shot would continue to be its "first line of defense against Omicron."
The vaccine maker said the decision to focus on the current vaccine, mRNA-1273, was driven in part by how quickly the recently discovered variant is spreading.
The company still plans to develop a vaccine to protect against Omicron and hopes to start clinical trials early next year, it said.
Moderna's shares rose 6.7% to $314.51 in early trading.
"What we have available right now is 1273," Dr. Paul Burton, Moderna's chief medical officer, said in an interview. "It's highly effective, and it's extremely safe. I think it will protect people through the coming holiday period and through these winter months when we're going to see the most severe pressure of Omicron."
The company said a two-dose course of its vaccine generated low neutralizing antibodies against the Omicron variant, but a 50 microgram booster dose increased neutralizing antibodies against the variant 37 fold. A higher, 100 microgram booster dose of the same vaccine drove antibody levels even higher - more than 80 times pre-boost levels.
Moderna President Stephen Hoge said on a conference call the company currently does not plan to pursue approval for that higher dose.
The antibody levels generated by the lower dose shot "are comfortably above" the levels that would signify a risk of 'breakthrough' infections for other variants of concern, Hoge said.
The data, which has not yet been peer-reviewed, tested blood from people who had received the vaccine against a pseudovirus engineered to resemble the Omicron variant. It is similar to data discussed last week by top U.S. infectious disease expert Anthony Fauci.
It may not be necessary to push up antibody levels even higher than those generated by the 50 microgram dose for many people, said Hoge. Governments could, however, choose a higher-dose version if they want to confer an enhanced level of protection.
"Could higher be better? Absolutely. But do we have data on that today to make a conclusive recommendation? No," said Hoge.
The company said that the 100 microgram dose was generally safe and well-tolerated, although there was a trend toward slightly more frequent adverse reactions.
U.S. regulators authorized the 50 microgram booster of Moderna's vaccine in October. The first two shots of Moderna's vaccine are both 100 micrograms.
Both the Moderna and the Pfizer (PFE.N)/BioNTech vaccines have been linked to rare cases of heart inflammation, particularly in young men. Several studies have suggested that Moderna's vaccine is likely to cause the heart inflammation at a higher rate than Pfizer's.
Omicron, a highly contagious variant first detected last month in southern Africa and Hong Kong, has raced around the globe and been reported in 89 countries, the World Health Organization said on Saturday.