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Pfizer and BioNTech have started a study comparing their Omicron-based Covid-19 vaccine to the original vaccine, the companies said in a statement on Tuesday.

If regulators were to decide to wait for data from such a study, it could mean it will be many months before an Omicron-specific vaccine would be available. 

Pfizer said it expects initial findings from the study, which will enroll 1,420 volunteers, to be available during the first half of 2022.

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However, it is not exactly clear what data regulators such as those at the Food and Drug Administration would require before authorizing an Omicron-specific vaccine, or what requirements the Centers for Disease Control and Prevention will have for recommending one.

We’re continuing to have an open dialogue with regulators and health authorities about an updated vaccine and ongoing data from the currently available vaccine – including what they would require,” a Pfizer spokesperson said via e-mail.

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A senior FDA official previously told STAT that the agency hopes to seek global consensus over whether new, variant-specific vaccines are needed and hopes to remain “cautious” and “agile.”

“We probably don’t want to take the chance that we’re going to abandon something that seems to be at least working reasonably well for something else unless we have good evidence that what we’re going to is going to be better,” the FDA official said.

In their statement, leaders from Pfizer and BioNTech emphasized that the current vaccines are effective at preventing severe disease and hospitalization due to Omicron.

“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,” said Kathrin U. Jansen, Pfizer’s senior vice president of vaccine research and development.

“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.

The new study, which has already enrolled its first volunteers, will follow adults 18 to 55 years of age, some of them taken from Pfizer and BioNTech’s studies of their authorized Covid-19 vaccine and booster. 

The study will look at the safety, immunogenicity, and tolerability of the vaccine – meaning, essentially, whether it raises antibody levels and how frequently it causes side effects including fever and fatigue. The study will not be large enough that it would be expected to necessarily give data on how strategies compare in terms of how many people are infected or develop Covid symptoms.

The study will be split into three groups, or cohorts. One, of 615 people, already received two doses of the authorized Pfizer-BioNTech vaccine. They will receive either one or two doses of the Omicron-specific vaccine.

A second group of 600 already received three doses of the Pfizer-BioNTech vaccine. They will receive either another dose of the authorized vaccine, or a dose of the Omicron-specific vaccine. A third group of 205 volunteers have not yet been vaccinated, and will receive three doses of the Omicron-based vaccine.

Pfizer’s CEO told CNBC earlier this month that the new vaccine would be ready in March, and that the company had already begun manufacturing doses. But this appears to refer to the ability to make the vaccine, not the more complicated steps that governments will have to take in order to decide whether to use it, which depend on how well existing vaccines prevent illness from the Omicron variant.

Speaking in December, Jansen, the Pfizer vaccine research executive, emphasized that the decision would require understanding the risks from Omicron and how well each vaccine protected recipients. “[W]e may build something Omicron-specific and then the next variant of concern is coming along and then we start all over again,” she warned. An Omicron booster would be ready if it is needed. “We look at the evidence. I think we are in a position to address it.”

When asked about the March timeframe, a Pfizer spokesperson responded:

“As COVID-19 continues to evolve and new variants emerge, developing updated versions of our vaccine may be necessary to offer people the highest level of protection against the virus. In the wake of Omicron, we are proactively investigating and manufacturing at risk an Omicron-based vaccine should it be needed.”

The Pfizer spokesperson said the company “will continue to share clinical and manufacturing updates related to this variant-based vaccine as they arise.”

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