COVID-19 vaccine antibodies wane within 6 months in older adults

Older adults in long-term care facilities see a rapid drop in antibody titres over the first 6 months after the second dose of the BNT162b2 vaccine for the coronavirus disease 2019 (COVID-19), reports a recent study.

“Age, sex, comorbidities, and cognitive status do not affect kinetics or extent of antibody decline,” the researchers said, adding that prior COVID-19 infection before the shot significantly slowed down this antibody decline. “These data support the immunization with a third dose in this vulnerable, high-risk population.”

The multicentre longitudinal cohort study included 127 residents (mean age 82.7 years, 90 women) who had been given two vaccine doses as per label. Antibody doses were measured 1 and 6 months after the second dose using the appropriate test kits.

Over the 6-month follow-up after vaccination, participants saw a median decrease of 77.6 percent in antibody titres, corresponding to a 0.47-decrease per day. Most patients (46.5 percent) lost between 70 percent and <90 percent of their antibody titres, while 21.3 percent saw a decrease between 50 percent and <70 percent.

Only two residents (1.6 percent) showed improving antibody responses over time, while three (2.3 percent) had stable values. Of note, participants who saw ≥90 percent antibody loss were more likely to present with at least one chronic condition associated with an impaired immune system, such as diabetes, chronic kidney disease, and hypothyroidism.

Cox proportional hazard analysis showed that only a prior infection of COVID-19 before vaccination was associated with lower risks of antibody loss >90 percent (hazard ratio [HR], 0.17, 95 percent confidence interval [CI], 0.07–0.41; p<0.001) or >70 percent (HR, 0.59, 95 percent CI, 0.38–0.94; p=0.025) after 6 months.