Author: Denise Baez
Neutralising titres against the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remained relatively high for up to 13 months post infection, with only modest declines in neutralising titres, according to a study published in the Journal of General Internal Medicine.
Patients with more severe disease showed higher rates of positivity over time suggesting a more robust antibody response, reported Juan P. Wisnivesky, MD, Icahn School of Medicine at Mount Sinai, New York, New York, and colleagues.
“Understanding immunological memory post-COVID-19 [coronavirus disease 2019] can provide insights into the risk for reinfection and the potential durability of vaccines,” the authors wrote. “While early reports suggested that antibody titres may rapidly decrease, other studies found high antibody titres several months after acute COVID-19 infection. However, many of these studies included relatively small samples and reported overall rates of positivity at titres that may not confer neutralising activity. We extend these results by showing persistent rates of a positive antibody response — at potentially neutralising titres — for up to 13 months after acute infection.”
The study cohort consisted of 620 adults (mean age, 49 years; 64% females; 53% white; 20% Latinx) who had recovered from COVID-19 and were enrolled in a prospective research registry at the Mount Sinai Health System between July 20, 2020, and April 13, 2021. All participants had laboratory-confirmed COVID-19 infection and had not received COVID-19 vaccination before enrolment or during the follow-up period. The participants contributed a total of 1,195 antibody tests.
The researchers used an enzyme-linked immunosorbent assay based on the stabilised full-length spike protein to assess SARS-CoV-2 antibodies from at least 30 days to up to 13 months after acute infection. A titer ≥1:320 (≥16 AU/mL) has been correlated with ≥90% neutralising activity in a micro-neutralisation assay and has been used as a criterion for convalescent plasma donation.
Overall, 90% of participants had positive antibody tests 6 months post-infection, and 83% had positive antibody tests 13 months post-COVID-19. Antibody titres were relatively stable over 13 months post infection.
The adjusted probability of having a positive antibody test at 13 months was 71% for outpatients, 75% for patients who presented to the emergency department, and 84% for patients who required hospitalisation.
“Rates of positive antibody tests against SARS-CoV-2 remained high up to 13 months post-COVID-19,” the authors wrote. “Patients treated in the hospital had significantly higher rates of positive results compared with those who were managed in the outpatient setting. There were no significant differences among patients treated in the emergency department or managed as outpatients for acute COVID-19.”
The researchers noted that they did not have information on severity of outpatient illness, therefore, they were not able to compare the immune response in asymptomatic patients compared with patients with mild or moderate COVID-19.