Pfizer booster proves effective against Omicron

As fears around Omicron swirl, Pfizer has announced that preliminary laboratory studies suggest that three doses of its Comirnaty vaccine offer effective protection against the new COVID-19 variant.

The early data suggests that a third dose produces a 25-fold increase in the level and presence of neutralising antibodies compared to just two doses. This is comparable to the relative effectiveness of two doses against Alpha, which is considered highly effective.

Pfizer also notes that antibodies recognise at least 80% of the epitopes – the part of the spike protein to which antibodies attach – in the Omicron variant, so two doses may still help lower severe disease symptoms.

In the public statement, Pfizer says it is continuing development of a vaccine that specifically protects against Omicron, which it hopes to have available by March.

“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,” says Albert Bourla, Pfizer’s chairman and chief executive officer. “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.”

“I would really like to stress that those who are fully vaccinated should also seek a booster when eligible, says Dr Vinod Balasubramaniam, a virologist at the Jeffrey Cheah School of Medicine & Health Sciences at Monash University Malaysia, who was not involved in the study.

“I think we have good reason to believe that the vaccines are effective, if not as effective, and that with boosters, they’ll be quite effective.”

Preliminary study shows change in antibodies

The preliminary study, which was conducted and funded by BioNTech and Pfizer, included 154 people who received three doses of the Pfizer vaccine. A blood sample was taken from each person one month after receiving the third dose, to assess the level of antibodies present that could potentially combat Omicron.

This was compared to 398 people who received three doses and were assessed for antibody effectiveness against Delta, and a further 155 people who received two doses and were assessed for effectiveness against the original Alpha strain.

The study found that, after three doses, antibodies neutralised the Omicron variant significantly better than after only two doses.

The need for real world data to really understand Omicron

Further samples will be taken to see how this effectiveness lasts over time, as preliminary data needs to be viewed with caution.

“There is currently little data available to determine the vaccine escape potential of Omicron,” says Adam Taylor, an emerging viruses researcher at Griffith University, who was not involved in the study.

“Data that is available is preliminary and lacks thorough scientific review. However, preliminary studies are suggesting that no matter which vaccine you’ve received or whether you’ve previously had covid, all combinations of vaccination or prior infection show a significant reduction in neutralising antibodies against Omicron.

“Antibody [assessments] are only one measure of vaccine effectiveness. The effectiveness of other arms of the protective immune response against Omicron remain unknown.

“Monitoring real world data, such as hospitalisations, will reveal the overall effectiveness of vaccination against disease caused by Omicron.”

Pfizer boosters effective in Israel

Pfizer booster shots have already been shown to be effective against the Delta variant, according to real-world data from Israel.

“The arrival of the Omicron variant of COVID-19, and other variants that will follow, also raises the question of how often boosters will be needed and how effective will this approach be as new variants arise,” says Roger Lord, a senior lecturer in medical science at Australian Catholic University, who was not involved in the study.

“The Pfizer COVID-19 vaccine does induce a significant amount of neutralising antibody, but further consideration may be needed for a more robust T-cell response. Booster vaccination to raise the level of neutralising antibody certainly helps to keep mortality caused by Delta low, but with new variants of the virus this protection is potentially compromised.

“The AstraZeneca COVID-19 vaccine, while previously reported to have a lower efficacy than the available mRNA COVID-19 vaccines, does induce a T-cell response, which may give rise to better protection from other COVID-19 variants.”