I have been eagerly awaiting more data about waning immunity 6 months after receiving the second dose of the Pfizer or Moderna mRNA vaccines. It has arrived this third week of September, with two important publications in the journal Science, and a split decision by the Federal Drug Administration (FDA) on the Pfizer application for boosters for all adults.
The two papers in Science ((J. Mateus et al., Science 10.1126/science.abj9853 (2021); Pegu, A. et al., Science 373:6561, pp 1372-1377, DOI 10.1126/science.abj4176 (2021)) examined immune responses in three age groups at 6 months after the second dose of the Moderna vaccine; 18-55, 56-70, and over 70 years old. Both virus-neutralizing antibody and cellular immunity were detected in the Mateus study in all participants, but antibody levels were significantly lower in the over 70 age group at 6 months compared to the under 55 age group. This was an important finding given that all age groups had an equivalent and stronger response at 2 weeks after the second shot. The Pegu study examined antibody responses to all of the SARS-CoV2 variants (including the prevalent Delta variant), and they found diminished responses to the vaccine strain and other variants in the over 70 age group. While the differences between age groups was not statistically significant because of the small group size (8), it was concerning that some of the over 70 age participants had no detectable antibody response against some of the virus variants.
It is expected that immunity will wane with increasing time after vaccination, but that does not mean that vaccines will fail to provide protection against serious disease. The first two doses of vaccine generate immune memory cells that should quickly respond to a new exposure to the SARS-CoV2 virus or a third booster of vaccine.
At their September 17th meeting, the FDA reached a split decision on the application for a third booster of the Pfizer vaccine. The FDA recommended a third booster for those over 65 or anyone who is immune compromised, but it did not recommend the booster for healthy, younger individuals. There was vigorous debate among the experts at the FDA meeting, with the Israeli contingent presenting evidence that a third booster with the Pfizer vaccine helped avoid a fourth wave of infection with the Delta variant. It is up to the Center for Disease Control and Prevention (CDC) to make the final recommendation for the booster shots since the FDA role is primarily related to safety and efficacy.
I believe the available data support a booster shot for anyone over 65. I got my Moderna vaccine booster this month, and the side effects were no worse than the second dose. I think that the booster will help protect against emerging virus variants, which are sure to appear given the large number of unvaccinated individuals in our country.