Three new laboratory studies show troubling signs that two doses of the Pfizer-BioNTech coronavirus vaccine may not fully protect against the omicron variant. But the research also suggests that three doses may provide much better protection.

The omicron variant: The 'good,' 'bad,' and 'ugly' scenarios

Omicron continues to spread in the U.S.

Researchers have been scrambling to study the effectiveness of Covid-19 vaccines against omicron as the variant spreads rapidly around the world. CDC Director Rochelle Walensky on Tuesday said omicron has now been reported in 19 states, including Hawaii, Texas, and Massachusetts, and that she "expect[s] that number to continue to increase."

Booster dose may be needed to protect against omicron, Pfizer-BioNTech say

As the variant spreads, Pfizer and BioNTech on Wednesday reported results from an early laboratory study examining how effectively the companies' vaccine protects against omicron.

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In a laboratory setting, the researchers exposed antibodies from the blood of vaccinated individuals to two different coronavirus variants: omicron, and the "wild-type" or original variant that contains no major mutations. They then measured how effectively the vaccine-induced antibodies neutralized each version of the virus.

The researchers found that antibodies from individuals who had received two vaccine doses showed a 25-fold reduction in effectiveness against the omicron variant. This finding suggests that two doses alone "may not be sufficient to protect against infection" from omicron, Pfizer and BioNTech said.

However, antibodies from individuals who had received three vaccine doses were about as effective against omicron as against previous variants.

In a press release, the companies added that they don't believe the omicron variant will diminish the protective powers of T cells, another crucial aspect of the immune system's response against the virus. According to the companies, this means that "vaccinated individuals may still be protected against severe forms of the disease" after only two doses.

In a statement, Pfizer CEO Albert Bourla said, "Although two doses of the vaccine may still offer protection against severe disease caused by the omicron strain, it's clear from these preliminary data that protection is improved with a third dose of our vaccine."

He added, "Ensuring as many people as possible are fully vaccinated with the first two dose series and a booster remains the best course of action to prevent the spread of Covid-19."

Other early studies support the need for boosters against omicron

In addition to the Pfizer and BioNTech study, separate research announced Tuesday similarly showed signs that omicron may partially evade the antibodies generated after two vaccine doses.

Alex Sigal, the virologist who led the South African study, said that while laboratory tests show a large reduction in antibody effectiveness, that doesn't necessarily mean the virus will escape vaccine-induced immunity in real life.

"The vaccine takes a hit, but it is not a completely different ballgame," Sigal said. "The escape of this variant is robust, it's extensive. But it's not complete."

"A good booster probably would decrease your chance of infection, especially infection leading to more severe disease," he added. "People who haven't had a booster should get one, and people who previously were infected should get vaccinated."

According to several experts, larger studies and more real-world data will be needed to effectively gauge the risk omicron poses to immunity.

"Extrapolating from … lab assays to what happens clinically is uncertain. What remains the most important indicator [of] how serious a threat omicron poses to fully vaccinated people will come from hospitalization data in the coming weeks,” said John Moore, an immunologist at Weill Cornell Medicine.

Separately, Stephen Goldstein, an evolutionary virologist at the University of Utah, said, "More importantly [than lab studies] though will be epidemiological studies looking at the frequency of reinfections and breakthrough infections, as well as disease severity in those patients."

He added, "I am still optimistic that vaccination or prior infection will provide some measure of protection against severe disease." (Chappell, NPR, 12/7; Kopp, Roll Call, 12/7; LaFraniere/Weiland, New York Times, 12/8; Knutson, Axios, 12/8; Johnson, Washington Post, 12/8; Gumbrecht, CNN, 12/8; Pfizer press release, 12/8; Douglas/Hinshaw, Wall Street Journal, 12/7; Gale/Kresge, Bloomberg, 12/8; Johnson/Achenbach, Washington Post, 12/7)