Antibody responses to COVID-19 vaccines in older people: Recent evidence & local data

Older adults have weaker antibody responses to two doses of COVID-19 vaccines [ie, mRNA-based BNT162b2 vaccine and inactivated CZ02 vaccine] vs younger individuals, but a booster dose mounts SARS-CoV-2 neutralization activities to a high level, according to data presented at AIM 2022.

“Older adults are particularly at risk for severe COVID-19, and over 95 percent of COVID-19–related deaths occurred in the population 60 years of age or older,” said Professor Margaret Ip of the Department of Microbiology, Chinese University of Hong Kong (CUHK). “[Although] data on immune responses to COVID-19 vaccines in older people are limited … some literature on this vulnerable age group is available.”

A cross-sectional study revealed significantly lower antibody titre categories among older vs younger populations (r= -0.258; p<0.001) after two doses of CZ02. Antibody titres started to decrease after the third decade of life and significantly dropped after the sixth (p<0.001). [Rheumatol Int 2021;41:1429-1440]

Similarly, a recent prospective study showed very good vaccine responses after two doses of BNT162b2 in older residents of long-term care facilities. “[However,] older adults had reduced SARS-CoV-2–specific IgG levels and a significantly lower neutralization capacity vs younger individuals, suggesting a vaccine booster dose should be prioritized for this vulnerable population,” reported Ip. [Age Ageing 2022;doi:10.1093/ageing/afac101]

Notably, antibody levels waned with time over 6 months after the second dose of BNT162b2 in both younger [median age, 41 years] and older populations [median age, 79 years]. “A more rapid decline in antibody concentrations in older vs younger adults was observed [p=0.016], but a booster dose brought the antibody response back to a high level equivalent to that in younger adults after 1 month of boosting,” highlighted Ip. [J Infect Dis 2022;doi:10.1093/infdis/jiac199]

For those who received two doses of CZ02, antibody response to a booster dose of BNT162b2 was examined in another study. “After the second dose of CZ02, antibody response also waned over time, but the response was recovered by BNT162b2, which boosted anti-spike antibody titres,” reported Ip. [Emerg Infect Dis 2022;28:1237-1240]

A local prospective study by CUHK explored antibody responses to BNT162b2 or CZ02 in older people aged ≥70 years. “BNT162b2 demonstrated a higher positive rate of antibody response vs CZ02 [100 percent vs 80 percent] in older people,” reported Ip. “At 28 days after the second dose of vaccination, there was no significant difference in antibody responses between the robust group and the frail group, regardless of the type of vaccine they received [p=0.488 for BNT162b2 and p=0.521 for CZ02]. People in different frailty groups mounted equivalent antibody levels.” [Ip M, AIM 2022]

Both vaccines are well tolerated in older people. “Most of the adverse events [AEs] reported were localized reactions such as arm pain, injection site pain or injection site itch, which were transient,” said Ip. Other AEs, such as muscle pain, fatigue, fever, or dizziness, were not commonly seen in older people (<10 percent), according to local data.