Immunity against the omicron coronavirus variant fades rapidly 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.
Experts acknowledge the benefits of a third vaccine shot strengthening protection against serious illness or death. Although neutralizing antibodies has been the primary focus of studies evaluating vaccines, they are not the only part of the immune system protecting humans against disease.
T cells, located in the immune system, are less effective at preventing infection but they are more durable than antibodies and can reduce the chance of serious illness if infected. Experts believe that this property of the T cell is the primary function of the vaccination — not preventing infection, and being much more durable protection, including against omicron.
Here are a few key facts:
- Levels of omicron-specific “neutralizing” antibodies—which can target the virus and stop it from replicating—decline 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.
- Omicron-specific antibody levels increased after the third dose—nearly 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.
- The “transient” antibody response after doses two and three mean additional booster shots might be needed to combat the variant, particularly among older people, the researchers said.