Study: Pfizer’s COVID vaccine protection against omicron fades just weeks after second and third doses

Immunity against the omicron coronavirus variant fades quickly after a second and third dose of Pfizer and BioNTech’s Covid-19 vaccine, according to peer reviewed research published in JAMA Network Open on Friday.

Levels of omicron-specific “neutralizing” antibodies, which can target the virus and stop it from replicating, reduce rapidly after a second and third dose of Pfizer’s shot, according to the Danish study of 128 people who had received two or three doses.

Antibody levels, which are associated with protection against infection and disease, fell within weeks of getting the shots and were much lower than the level of antibodies specific to the original and delta coronavirus variants, the researchers said.

When compared to original and delta variants, the proportion of omicron-specific antibodies detected in participants’ blood dropped “rapidly” from 76% four weeks after the second shot to 53% at weeks eight to 10 and 19% at weeks 12 to 14, the researchers found.

Omicron-specific antibody levels increased after the third dose, close 21-fold at week three and nearly 8-fold at week four, compared to four weeks after the second dose, and the shot generated a detectable response in most people for at least eight weeks, the researchers said.

However, antibody levels started to drop as early as three weeks after the booster shot, falling 4.9-fold for the original variant, 5.6-fold for delta and 5.4-fold for omicron between weeks three and eight.

Experts and regulators largely accept the benefits of a third vaccine dose to offer additional protection against serious illness or death. There is less agreement over whether additional shots are needed after the booster shot and also whether frequent boosting will be both practical and feasible.