People older than 80 years were found to have lower SARS-CoV-2-specific immunoglobulin G (IgG) antibody titers and neutralizing titers compared with people younger than 60 years after the first and second doses of the Pfizer-BioNTech COVID-19 vaccine, according to study results published in Clinical Infectious Diseases. Findings from the study suggest that people older than 80 years may require earlier revaccination to ensure strong immunity and protection against infection.
To compare the induction of immune responses between people younger than 60 years (younger vaccinees) and people older than 80 years (older vaccinees), the study authors collected blood samples from vaccinated people in a nursing home in Cologne, Germany, beginning at the end of December 2020 when the vaccination campaign started.
SARS-CoV-2 spike-specific antibodies, IgG, and neutralization titers were compared 17 to 19 days after the first dose and 17 days after the second dose between younger and older vaccinees. Blood samples were collected from 176 participants: 91 younger vaccinees (mean age, 42.2 years; 68% women) and 85 older vaccinees (mean age, 87.9 years; 73% women). The final analysis excluded 3 participants who tested positive for SARS-CoV-2.
After the first dose, SARS-CoV-2 spike-specific IgG titers were significantly higher in younger vaccinees (mean, 313.3 binding antibody units [BAU]/mL; range, 0-3840.0 BAU/mL) compared with older vaccinees (mean 41.2 BAU/mL, range 0-484.7 BAU/mL; P <.0001).
Although IgG titers increased between the first and second dose among older vaccinees, they remained 2.8-fold lower after the second dose when compared with younger vaccinees (P <.0001). After the second dose, the mean titer for younger vaccinees increased to 3702 BAU/mL (range, 81.6-32000.0 BAU/mL), but the mean titer for older vaccinees increased to 1332 BAU/mL (range 0-16891 BAU/mL) with 10.6% of older vaccinees remaining below the cutoff (>35.6 BAU/mL).
The neutralizing antibody response was similarly lower in older vaccinees. After the second dose, 31.3% of the older vaccinees had no detectable neutralizing antibodies vs only 2.2% in the younger group.
The presence or absence of postvaccination reactions did not correlate with antibody response.
“The main differences between the 2 groups are likely a consequence of immunosenescence,” the study authors suggested. Because it is not yet clear how long the mRNA vaccine provides protection from SARS-CoV-2 infection, “it might be necessary to have strategies…to overcome possible age-related limitations for COVID-19 vaccination,” the study authors concluded.
Müller L, Andrée M, Moskorz W, et al. Age-dependent immune response to the Biontech/Pfizer BNT162b2 COVID-19 vaccination. Clin Infect Dis. Published online April 27, 2021. doi:10.1093/cid/ciab381