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Omicron cuts Pfizer vaccine’s potency, but data show booster may restore protection

Three doses of Pfizer and BioNTech’s COVID-19 vaccine may protect against the new omicron variant similarly well as two doses did against the original coronavirus strain, according to preliminary data from laboratory testing released by the companies Wednesday.

Blood samples from individuals who only received two doses of the shot, however, showed a significant reduction in virus-neutralizing antibodies when tested against omicron, suggesting that people who have not received a booster may be vulnerable to infection.

“The new data … shows us that the first line of defense with two doses of vaccination might be compromised and three doses of vaccination are required to restore protection,” said Ugur Sahin, BioNTech’s CEO, in a press conference Wednesday.

The results, which were released via press release and are not peer reviewed, both highlight the threat posed by omicron and offer some hope that vaccines can still effectively guard against the variant. Importantly, Pfizer and BioNTech, as well as many scientists, expect that vaccination should still prevent severe disease, even without a booster dose.

Researchers around the world have rushed to assess omicron’s potential to evade the immune defenses generated by vaccination or past infection. The data from Pfizer and BioNTech are some of the first to emerge since omicron’s identification by scientists in South Africa roughly two weeks ago. The large number of mutations found in omicron, particularly in regions of the virus that are targeted by COVID-19 vaccines, quickly led to alarm that it may pose a greater danger than the now dominant delta variant.

While there are some tentative signs that omicron infections may result in more mild cases, much remains unclear about the variant, including how its genetic differences will affect the protection of available vaccines.

An unpublished study, released online Tuesday by scientists from the Africa Health Research Institute, gave the first glimpse. Their data showed that, while omicron does not completely escape Pfizer and BioNTech’s vaccine, neutralizing antibody levels after two doses were as much as 40-fold lower versus the variant than against the original coronavirus strain. That figure, however, is preliminary and could be adjusted as more research is completed.

Pfizer and BioNTech’s results indicated a smaller, but still significant, 25-fold reduction in antibody levels versus omicron after two doses. A third dose, however, raised antibody levels by a similar amount, roughly matching the response generated against the original coronavirus strain by two doses. It’s unclear how long the additional benefits of the booster might last, though, or whether another shot would eventually be required to maintain protection.

The data show omicron is “still not a complete escape variant,” BioNTech’s Sahin said Wednesday. “It is a partial escape variant, and that means the virus can be neutralized by high [levels] of neutralizing antibodies.”

Antibody levels, while correlated with the degree of vaccine protection, aren’t the only immune defenders that respond to viral infections. Researchers, as well as Pfizer and BioNTech, think immune cells known as T cells could play an important role in protecting against COVID-19, particularly more severe disease.

According to the companies, T cells stirred up by vaccination target areas on the coronavirus that are largely not affected by omicron’s many mutations.

As T cells and other parts of the immune system play a role in protection, reductions in antibody levels may not translate exactly to lower efficacy. A 25-fold drop in antibodies, for instance, doesn’t necessarily indicate a 25-fold decline in overall vaccine effectiveness.

Pfizer and BioNTech carried out this first round of testing using engineered “pseudo-virus” forms of omicron, which may not fully replicate the antibody response to the live virus. The companies are conducting additional laboratory testing.

While a booster may maintain protection versus omicron, the drugmakers are still moving forward with development of an omicron-specific booster, as are other vaccine makers like Moderna.

Work on that shot began Nov. 25 and the companies expect they could have it ready within 100 days, depending on the amount of testing regulators might require. Pfizer and BioNTech are currently targeting availability by March, although Sahin said Wednesday it’s still not clear whether an omicron booster would be needed.

“In the next few weeks more data will emerge in order to answer the question whether or not or when we need an omicron vaccine,” Sahin said.

Pfizer and BioNTech anticipate they can produce 4 billion doses of their vaccine next year, and could transition some of that capacity toward an omicron booster. Initially, however, supplies of a tailored shot wouldn’t be broadly available, Sahin said.