Background SARS-CoV-2 IgG antibody measurements can be used to estimate the proportion of a population exposed or infected and may be informative about the risk of future infection. Previous estimates of the duration of antibody responses vary. Methods We present 6 months of data from a longitudinal seroprevalence study of 3276 UK healthcare workers (HCWs). Serial measurements of SARS-CoV-2 anti-nucleocapsid and anti-spike IgG were obtained. Interval censored survival analysis was used to investigate the duration of detectable responses. Additionally, Bayesian mixed linear models were used to investigate anti-nucleocapsid waning. Results Anti-spike IgG levels remained stably detected after a positive result, e.g., in 94% (95% credibility interval, CrI, 91-96%) of HCWs at 180 days. Anti-nucleocapsid IgG levels rose to a peak at 24 (95% credibility interval, CrI 19-31) days post first PCR-positive test, before beginning to fall. Considering 452 anti-nucleocapsid seropositive HCWs over a median of 121 days from their maximum positive IgG titre, the mean estimated antibody half-life was 85 (95%CrI, 81-90) days. Higher maximum observed anti-nucleocapsid titres were associated with longer estimated antibody half-lives. Increasing age, Asian ethnicity and prior self-reported symptoms were independently associated with higher maximum anti-nucleocapsid levels and increasing age and a positive PCR test undertaken for symptoms with longer anti-nucleocapsid half-lives. Conclusion SARS-CoV-2 anti-nucleocapsid antibodies wane within months, and faster in younger adults and those without symptoms. However, anti-spike IgG remains stably detected. Ongoing longitudinal studies are required to track the long-term duration of antibody levels and their association with immunity to SARS-CoV-2 reinfection.

COVID-19 disease is caused by the Betacoronavirus, SARS-CoV-2. This virus gave rise to 676 million confirmed cases with 6.9 million deaths worldwide by early 2023. After first appearing in Wuhan, China in late 2019, the virus has mutated into seven successive major forms with progressive increases in infectivity: Alpha, Beta, Delta, Omicron, and Omicron variants BA.4, BA.5, and XBB.1.5. Liposomal mRNA vaccines have been developed against SARS-CoV-2. Many of these received Emergency-use Authorization, and all have been highly promoted by civil authorities and the media. On the other hand, therapeutics against COVID-19 have been developed, but some of these have been severely suppressed, even by reliance on retracted papers. Our laboratory found that chlorpheniramine maleate, an over-the- counter antihistamine, was active against the Coronavirus through drug-database searches, molecular modeling, and a preliminary retrospective clinical-study. The manuscript that described this work was rejected by several journal editors without peer review, thus providing further direct evidence for suppression of small-molecule therapeutics. Epidemiologic study of death statistics in the VAERS database showed that 19,710 people lost their lives after COVID-19 vaccination; mortality from all other common vaccines does not sum to even 20% of this staggering value. The vaccine has also been responsible for significant morbidity. A consensus has begun to develop among physicians and scientists that COVID-19 disease and vaccination both result in chronic symptoms in many people, now called “Long COVID” or “Long-hauler’s syndrome”. Thus, vaccination does not appear to be a reasonable approach to combat COVID-19 disease. In view of this, development, testing, and approval or repurposing of therapeutics is imperative, especially as we observe recent increases in mortality due to COVID-19 Omicron XBB.1.5. Chlorpheniramine maleate, an over-the-counter medication, is uniquely positioned to serve as a broad-spectrum antiviral against SARS-CoV-2 and other viruses in this post- pandemic age.