Background
While correlates of protection against symptomatic and severe breakthrough SARS-CoV-2 infections are well characterized, correlates of protection against virus transmission are incompletely understood.
Methods
We studied a Croatian cohort of individuals with documented household exposure to SARS-CoV-2 in December 2022. Sera were acquired prior to symptom onset, at the time of the
... [Show full abstract] COVID-19 diagnosis of the index cases, and comprehensively analyzed for correlates of protection against virus transmission. We monitored participants for 14 days and tested them with PCR at the end of the observation period to identify any virus transmission, including asymptomatic ones.
Interpretation
Out of nearly 200 tested serological parameters, 22 features were significantly different between the infected and the uninfected participants. Titers of variant-specific neutralizing antibody showed the biggest difference and were significantly higher in the uninfected subgroup. Some infected individuals with strong IgM responses to the spike antigen showed robust neutralization titers as well. Since IgM is likely an indication of recent antigenic exposure, data were reanalyzed by excluding such values. This refined analysis showed a complete segregation of infected and uninfected individuals into groups with low and high variant-specific neutralization titers. Therefore, our data indicate that high neutralizing titers are correlates of protection against SARS-CoV-2 transmission in intense contacts among household members.