Neutralizing antibody responses in asymptomatic close contacts of COVID-19 patients and in asymptomatic healthcare workers.

The identification of novel antibodies that could neutralize SARS-CoV-2 is one of the novel approaches to use in combating COVID-19. This study aimed to explore the level of neutralizing antibodies (NAbs) in asymptomatic close contacts of COVID-19 patients and asymptomatic healthcare workers. In vitro qualitative detection of serum antibodies of participants from both populations was done using an anti-SARS-CoV-2 immunoassay. The study included 107 participants, of which 59.8% were healthcare workers and 40.2% were family contacts of confirmed COVID-19 cases. Their median age was 22 years. The percentage of positivity and median titer for NAbs were significantly higher among family contacts than mong healthcare workers (P = 0.013 and < 0.001, respectively). We also measured C-reactive protein (CRP) levels and the median value of CRP was significantly higher in the family members who had been in contact with COVID-19 patients than in healthcare workers (P < 0.001). In the family contact group, there was a significant negative correlation between the absolute lymphocyte count and CRP (r = -0.409, P = 0.034). There was no significant correlation between neutralizing antibody titers and either CRP or absolute lymphocyte count (P > 0.05 for both). In conclusion, the indication of elevated NAb titers in asymptomatic family contacts could help lay the groundwork for further studies to explore the potential utility of these antibodies to provide future immunity from infection within a family as well as for potential use in general during passive antibody therapies for COVID-19 patients.