Unvaccinated older adults have the highest level of SARS-CoV-2 antibodies following infection but also experience the most rapid rate of antibody decay, indicating the importance of COVID-19 booster vaccination among this population. These study results were published in Open Forum Infectious Disease.
In this cross-sectional cohort study, researchers analyzed SARS-CoV-2 antibody levels among unvaccinated older adults following the onset of COVID-19 infection. Residual serum and plasma samples were collected from patients undergoing polymerase chain reaction (PCR) testing for COVID-19 infection at a community laboratory in Canada between April and September of 2020. The researchers used a high-throughput chemiluminescent enzyme-linked immunosorbent assay to quantify any immunoglobulin (Ig)G, IgA, and IgM antibodies against COVID-19 nucleocapsid, trimeric spike, and its receptor-binding domain (RBD). A surrogate high-throughput protein-based neutralization assay was used to quantify neutralization efficiency.
Among 739 patients included in the analysis, the median age was 82 years, 75% were older than 65 years, 34.1% were men, and 72.1% had PCR-confirmed COVID-19 infection.
The researchers evaluated the effect of age on antibody response after dividing COVID-19-positive patients into 3 age groups, including those younger than 65 years (n=126), those between 65 and 89 years (n=252), and those 90 years and older (n=135).
Patients younger than 65 years had significantly lower antispike, anti-RBD, and antinucleocapsid IgG antibodies when compared with those between 65 and 89 years and those 90 years and older. Similar results were noted for IgA levels, with the lowest antispike (P <.01), anti-RBD (P <.01), and antinucleocapsid (P <.01) antibodies observed among patients younger than 65 years. Patients younger than 65 years also had the lowest overall antinucleocapid IgG levels (P =.0025).
Further analysis showed patients younger than 65 years had significantly lower median neutralization efficiency when compared with those between 65 and 89 years (P =.000005) and those aged 90 years and older (P =.00019).
The researchers assessed the relationship between antibody levels, the time of sample collection, and age using a generalized linear model with a gamma regression. Although patients aged 90 years and older initially had the highest overall antispike and antinucleocapid IgG antibody levels, they experienced the most rapid overall rate of antibody decay.
Of note, antispike and antinucleocapsid IgG antibody levels among patients aged 90 years and older were similar or lower than the levels observed among those in younger age groups by day 100 after symptom onset. In addition, the rate of IgA and IgM antibody decay was also the fastest among patients aged 90 years and older.
With the exception of reduced antinucleocapsid IgG, antispike IgA, and antinucleocapid IgA levels, little variation in IgG, IgA, and IgM antibody levels was observed among patients younger than 65 years over time.
Study limitations include the lack of information on disease severity and potential confounding due to delayed sera collection for some patients. The researchers also noted that immunologic recall from prior infections may have contributed to differences in antibody levels observed among the patient population.
According to the researchers, “[A]lthough younger individuals mount a less potent response following SARS-CoV-2 infection, their antibody levels are more stable during the 100 days period that was studied than older individuals.”
This article originally appeared on Infectious Disease Advisor
Whelan M, Galipeau Y, White-Al Habeeb N, et al. Cross-sectional characterization of SARS-COV-2 antibody levels and decay rates following infection of unvaccinated elderly individuals. Open Forum Infect Dis. Published online July 20, 2023. doi:10.1093/ofid/ofad384