Pfizer and BioNTech have started testing an Omicron-specific COVID-19 vaccine for adults

• Pfizer and BioNTech are starting clinical trials for an Omicron-specific COVID-19 vaccine on adults.
• The study will be evaluated in 1,400 adults ages 18 to 55, the two companies said Tuesday.

Pfizer and BioNTech are starting clinical trials for an Omicron-specific coronavirus vaccine for adults, the two companies announced Tuesday.

The study, which will measure the "safety, tolerability and immunogenicity" of a COVID-19 vaccine tailored to the highly transmissible variant, will be evaluated in 1,400 adults ages 18 to 55.

"While current research and real-world data show that boosters continue to provide a high level of protection against severe disease and hospitalization with Omicron, we recognize the need to be prepared in the event this protection wanes over time and to potentially help address Omicron and new variants in the future," Kathrin Jansen, Pfizer's senior vice president, said in a statement.

Mikael Dolsten, Pfizer's chief scientific officer, told Insider's Andrew Dunn earlier this month that the shot would be ready by late March.

But it was unclear whether the Omicron-specific shot would be needed, Dolsten said at the time.

Data from the Centers for Disease Control and Prevention indicates that two-shot vaccine protection is less effective against Omicron than it is against the previously dominant Delta variant — and immunity against both strains wanes just six months after a person receives a second dose.

A CDC study found that a booster shot's effectiveness at preventing hospitalization from the Omicron variant was 90%, up from 57% effectiveness 26 weeks after a second dose, Insider previously reported.

"I don't know if we will need it. I don't know if it will be used, but it will be ready." Pfizer CEO Albert Bourla told CNBC earlier in January.

The two companies' announcement came as the US was averaging nearly 664,000 daily new COVID-19 cases, according to the latest CDC data, down from a mid-January peak of about 800,000 daily cases.

According to the latest CDC estimates, the highly transmissible Omicron variant accounts for over 99% of all COVID-19 infections in the country.