In a joint statement issued on Dec. 8, the American and German partners said results from an initial lab study showed that a third dose of their Comirnarty shot can increase antibody protection 25-fold compared with the initial two-dose series against the original strain of the virus. That was the good news, along with assurances by the vaccine makers that their two-dose regimen approved almost worldwide over the past year is still effective enough to prevent serious illness and death. 

The not-so-good news was that the efficacy of two doses was seen to be “significantly” lower against the Omicron variant. A fourth dose may be needed in less than a year after the third, Pfizer CEO Albert Bourla said in US media interviews. “When we see real-world data, will determine if the omicron is well covered by the third dose and for how long,” he said, adding that these results, expected to be released over the next two weeks, will be more accurate.

Tests carried out in US and South Africa

A small preliminary study conducted by a South African research team tested blood samples of 12 people who had previously been vaccinated with the Pfizer/BioNTech vaccine and found a 41-fold drop in the ability of the antibodies to neutralize the omicron variant compared with the original virus strain. The team also found that omicron attaches to the same receptor, known as ACE2, to infect human lung cells that previous variants used.

Explaining the methodology of their own efficacy calculation against the Omicron variant, Pfizer and BioNTech said they tested a panel of human immune sera obtained from the blood of individuals that had received two or three 30-µg doses of the current Pfizer-BioNTech Covid vaccine, using a pseudovirus neutralization test (pVNT). Sera collected from participants three weeks after receiving the second dose or one month after the third dose were tested simultaneously for their neutralizing antibody titer against the wild-type SARS-Cov-2 spike protein, and the Omicron spike variant.

It was the third dose that significantly increased the neutralizing antibody titers against the Omicron strain spike, the companies said. Neutralization after three doses was comparable to the neutralization against the wild-type strain observed in sera from individuals who received two doses of the companies’ Covid-19 vaccine, and offered around 95% protection.

Ugur Sahin, CEO and co-founder of Mainz-based BioNTech, which owns the proprietary mRNA technology and holds the marketing authorization rights in most countries where the vaccine is sold, said the partners began work at the end of November on an adaptation of their original shot, aiming to increase the level and duration of protection against Omicron. First batches of the adapted version can be produced and be ready for delivery within 100 days, pending regulatory approval, he added.

Pfizer and BioNTech have also tested other variant-specific vaccines that have produced very strong neutralization titers and a tolerable safety profile, Sahin noted. Based on this experience, they have “high confidence” that they can deliver an Omicron-based vaccine by March 2022 if needed.

The vaccine makers plan to submit the data they have collected against other Covid variants to international regulatory agencies to help accelerate the process of adapting the vaccine and gaining regulatory authorization or approval of an Omicron-specific vaccine. By the end of December, they anticipate having enough data to determine whether a booster dose is enough to fight omicron or if they will have to produce a new vaccine.

Author: Dede Williams, Freelance Journalist