Incidence of SARS-CoV-2 infection in health care workers from Northern Italy based on antibody status: immune protection from secondary infection- A retrospective observational case-controlled study

• Published in: International journal of infectious diseases Vol. 109; pp. 199 - 202
• Main Authors: Rovida, Francesca, Cassaniti, Irene, Percivalle, Elena, Sarasini, Antonella, Paolucci, Stefania, Klersy, Catherine, Cutti, Sara, Novelli, Viola, Marena, Carlo, Luzzaro, Francesco, De Vito, Giovanni, Schiavo, Roberta, Lo Cascio, Giuliana, Lilleri, Daniele, Baldanti, Fausto
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2021; Elsevier
• Subjects: immune protection; neutralizing antibody; SARS-CoV-2 infection; secondary infection; SARS-CoV-2 infection; neutralizing antibody; immune protection; secondary infection
• DOI: 10.1016/j.ijid.2021.07.003
• ISSN: 1201-9712

•Immunity from natural SARS-CoV-2 infection is protective in healthcare workers•Secondary infection is associated with low or absent serum neutralizing titer•Anti-Spike IgG were not significantly lower in subjects with secondary infections•Secondary infection is usually asymptomatic or mildly symptomatic•Vaccination of SARS-CoV-2-seronegative subjects might be prioritized The protection from SARS-CoV-2 infection induced by SARS-CoV-2 anti-S1 and anti-S2 IgG antibody positivity resulting from natural infection was evaluated. The frequency of SARS-CoV-2 infection (as determined by virus RNA detection) was evaluated in a group of 1,460 seropositive and a control group of 8,150 seronegative healthcare workers in three Centres of Northern Italy in the period June-November 2020. Neutralizing serum titers were analyzed in seropositive subjects with or without secondary SARS-CoV-2 infection. During the 6-month survey, 1.78% seropositive subjects developed secondary SARS-CoV-2 infection while 6.63% seronegative controls developed primary infection (odds ratio: 0.26; 95% confidence interval: 0.17-0.38). Secondary infection was associated with low or absent serum neutralizing titer (p<0.01) and was mildly symptomatic in 45.8% cases vs 71.4% symptomatic primary infections (odds ratio: 0.34; 95% confidence interval: 0.16-0.78). Immunity from natural infection appears protective from secondary infection; therefore, vaccination of seronegative subjects might be prioritized.