Long-term persistence of SARS-CoV-2 neutralizing antibody responses after infection and estimates of the duration of protection
Eric H. Y. Lau, David S.C. Hui, Owen TY Tsang, Wai Hung Chan, Mike Yat Wah Kwan, Susan S. Chiu, Samuel M. S. Cheng, Ronald LW Ko, John KC Li, Sara Chaothai, Chi H. Tsang, Leo L. M. Poon, Malik Peiris
Abstract
Background: The duration of immunity in SARS-CoV-2 infected people remains unclear. Neutralizing antibody responses are the best available correlate of protection against re-infection. Recent studies estimated that the correlate of 50% protection from re-infection was 20% of the mean convalescent neutralizing antibody titre. Methods: We collected sera from a cohort of 124 individuals with RT-PCR confirmed SARS-CoV-2 infections from Prince of Wales Hospital, Princess Margaret Hospital, Queen Elizabeth Hospital and Queen Mary Hospitals of the Hospital Authority of Hong Kong, for periods up to 386 days after symptom onset and tested these for antibody to SARS-CoV-2 using 50% virus plaque reduction neutralization tests (PRNT 50 ), surrogate neutralization tests and spike receptor binding domain (RBD) binding antibody. Patients were recruited from 21 January 2020 to 16 February 2021 and follow-up samples were collected until 9th March 2021. Findings: Because the rate of antibody waning slows with time, we fitted lines of decay to 115 sera from 62 patients collected beyond 90 days after symptom onset and estimate that PRNT 50 antibody will remain detectable for around 1,717 days after symptom onset and that levels conferring 50% protection will be maintained for around 990 days post-symptom onset, in symptomatic patients. This would potentially be affected by emerging virus variants. PRNT titres wane faster in children. There was a high level of correlation between PRNT 50 antibody titers and the % of inhibition in surrogate virus neutralization tests. Interpretation: The data suggest that symptomatic COVID-19 disease is followed by relatively long-lived protection from re-infection by antigenically similar viruses.