The fall in antibody response to SARS-CoV-2: a longitudinal study of asymptomatic to critically ill patients up to 10 months after recovery.

Peghin, Maddalena; De Martino, Maria; Fabris, Martina; Palese, Alvisa; Visintini, Erica; Graziano, Elena; Gerussi, Valentina; Bontempo, Giulia; Federica, D'Aurizio; Biasotto, Alessia; Sartor, Assunta; Pipan, Corrado; Marzinotto, Stefania; Curcio, Francesco; Bouza, Emilio; Isola, Miriam; Tascini, Carlo

Background. The aim was to assess long-term dynamics and factors associated with the serological response against the Severe Acute Respiratory Syndrome Coronavirus 2 after primary infection. Methods. A prospective longitudinal study with monthly serological follow-up during the first 4 months, and then at 6, 8 and 10 months after the disease onset of all recovered adult in- and out-patients with Coronavirus Disease 2019 (COVID-19) attending Udine Hospital (Italy) during the first wave (from March to May 2020). Results. 542 individuals were included (289 female, mean age 53.1 years), mostly with mild COVID-19 (370, 68.3%). Patients were followed for a median of 302 days (Interquartile Range, 186-311). Overall seroconversion rate within two months was 32% for IgM and 90% for IgG. Seroreversion was observed in 90% of patients for IgM at 4 months and in 47% for IgG at 10 months. older age, number of symptoms at acute onset, severity of acute COVID-19, were all independent predictors of long-term immunity both for IgM (β, linear regression coefficient, 1.10, p=0.001; β 5.15 p=0.014; β 43.84 p=0.021, respectively) and for IgG (β 1.43 p<0.001; β 10.46 p<0.001; β 46.79 p<0.001, respectively), whereas the initial IgG peak was associated only with IgG duration (β 1.12, p <0.001). Conclusions. IgM antibodies disappeared at four months and IgG antibodies declined in about half of patients 10 months after acute COVID-19. These effects varied depending on the intensity of the initial antibody response, age and burden of acute COVID-19.