SAN FRANCISCO (KRON) – Pfizer and its partner BioNTech are starting clinical trials for an omicron variant-specific COVID-19 vaccine for adults ages 18-55, the companies announced Tuesday.

The study will include three cohorts, the companies said, the first having 615 participants, the second with 600 participants, and the third with 205 participants. Some of them have also participated in the companies’ Phase 3 COVID-19 booster study, they said.

“Vaccines continue to offer strong protection against severe disease caused by omicron. Yet, emerging data indicate vaccine-induced protection against infection and mild to moderate disease wanes more rapidly than was observed with prior strains,” said Ugur Sahin, CEO and co-founder of BioNTech, in a press release. “This study is part of our science-based approach to develop a variant-based vaccine that achieves a similar level of protection against omicron as it did with earlier variants but with longer duration of protection.”

Here is what part of the study entails, according to the companies:

  • Cohort #1: Received two doses of the current Pfizer-BioNTech COVID-19 vaccine 90-180 days prior to enrollment; in the study, participants will receive one or two doses of the omicron-based vaccine
  • Cohort #2: Received three doses of the current Pfizer-BioNTech COVID-19 vaccine 90-180 days prior to enrollment; in the study, participants will receive one dose of the current Pfizer-BioNTech COVID-19 vaccine or the omicron-based vaccine
  • Cohort #3: Vaccine-naïve participants will receive three doses of the omicron-based vaccine

Pfizer’s CEO has previously said they expect to have a vaccine targeting omicron ready by March 2022, The Hill reported.

While omicron is more likely than previous variants to cause infection even in people who’ve been vaccinated, it’s not yet clear that a change to the vaccine is needed.

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Infectious disease expert Dr. Anthony Fauci has said there is no need for a variant-specific vaccine since the booster shots appear to be effective against preventing COVID-19 hospitalizations.

The Associated Press contributed to this report.