Do Age and Gender Affect Immune Response to COVID-19 Vaccination?

There is a lack of evidence on whether certain populations have more robust immune responses to COVID-19 vaccination. One study, presented during the 32nd European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), examined secondary immune response by age and gender after Pfizer-BioNTech vaccination.

The study included 1920 healthcare workers, none of whom had a previous COVID-19 infection. The participants were 66% (n=1267) female and 34% (n=647) male. The cohort was tested for quantitative anti-receptor binding domain (anti-RBD) IgG expression at 30 days and 120 days after their second dose of the Pfizer-BioNTech (BNT162b2) mRNA COVID-19 vaccine.

After completing their primary vaccination series, 99.7% of the enrolled healthcare workers showed a strong antibody response within 30 days of their second dose, while 0.3% were considered “slow” or “non-responders.” After 120 days, 98.6% of participants displayed an antibody titer decay.

As expected, anti RBD IgG expression was inversely proportional with age, decreasing from 1800 Bau/mL in the 28–40-year-old cohort to 1250 Bau/mL in the 61–70-year-old cohort. The average participant age was 52 years (men averaged 54 and women averaged 52 years old).

Immune responses only differed by gender in the participants over 50 years of age. In this middle-aged cohort, females produced up to 20% more antibodies than males. This trend appeared at 30 days after the second vaccine dose, and remained through the 120-day checkpoint. Regression analysis of the time-dependent percentual decrease showed antibody titers consistently declined equal to 8.5 times the titer measured at 30 days after the second vaccine dose.

Constant time-dependent IgG anti RBD decrease appeared to be the same for all age groups. the one exception was young men (aged 28-40 years), in whom anti-RBD IgG decreased twice as slowly.

The investigators concluded that the decrease of anti-RBD IgG aligns with a consistent decline in kinetics that is largely distinct from age and gender. They noted that prior studies suggested differences in immune response to Pfizer-BioNTech vaccination by gender and age, but these only investigated antibody increase after the first dose. The study authors suggested further research could potentially identify a unique threshold value, below which neutralizing antibodies offer insufficient protection against COVID-19 reinfection.