SARS-CoV-2 Vaccination Elicits Unconventional IgM Specific Responses in Naïve and Previously COVID19-Infected Individuals

Background: IgG antibodies specific for the SARS-CoV-2 Spike protein are under intensive investigation urgent need to identify a correlate of protective immunity in individuals vaccinated with licensed and candidate COVID-19 vaccines. Limited data available on vaccine-elicited IgM their potential implication SARS-CoV-2. Methods: We performed longitudinal study quantify spike (IgG-S IgM-S) 1873 health care worker (HCW) recipients BNT162b2 (Comirnaty) vaccine. Samples were collected before administration (T0), at second dose (T1) three weeks after (T2). The cohort included 1584 immunologically naive (IN) 289 had history previous infection (PI). Findings: In IN we identified patterns responses: (a) positive/IgM negative (36.1%), (b) coordinated IgM-S/IgG-S responses appearing first (37.4%) (c) delayed (26.3%). Coordinated associated higher titers. Of PI vaccinees, 64.5% IgM-S positive vaccination, whereas 32% 3.5% developed vaccine respectively. sera pseudovirus neutralization titers compared negative. Similar results observed who received either Moderna or Astrazeneca. Interpretation: expression IgG-S vaccination was significantly more efficient response both antibody virus-neutralizing activity, representing protection. Instead, unconventional positive/IgM-S may be suggestive recruitment cross coronaviruses by warranting further investigation. Funding Information: This work supported Italian Ministry Health “Fondi Ricerca Corrente”- L1P5 “Progetto Finalizzata COVID-2020-12371675” IRCCS Sacro Cuore Don Calabria Hospital, FUR 2020 Department Excellence 2018-2022, MIUR, Italy Brain Research Foundation Verona.