More than 1 in 4 young adults test seropositive for COVID-19

A recent study has shown that more than a quarter of young adults are seropositive for SARS-CoV-2, many of whom show single positivity with IgM. Such seropositivity was higher among those who had cases of the coronavirus disease 2019 (COVID-19) in the household and those who used public transport.

Researchers conducted a population-based analysis, performing a COVID-19 follow-up of 980 participants (aged 24–27 years) from October 2020 to June 2021. Enzyme-linked immunosorbent assays were used to measure titres of SARS-CoV-2 receptor binding domain (RBD)-specific IgM, IgA, and IgG.  Clinical and epidemiological correlates of seropositivity were also assessed.

Moreover, the researchers also conducted a subpopulation analysis of 108 participants to assess virus-specific memory B- and T-cell responses.

In total, 277 serum samples tested positive for at least one isotype of anti-RBD immunoglobulin, yielding a seropositivity rate of 28.4 percent. The vast majority of samples (n=700; 71.6 percent) were triple-negative.

Disaggregating by individual isotypes showed that 11.8 percent, 6.8 percent, and 22.4 percent of sera were positive for IgM, IgA, and IgG, respectively. Most positive samples (27.8 percent) were positive for two isotypes, while only 8.7 percent were triple-positive. Almost half (43.3 percent) were positive for IgG alone, while 18.4 percent and 1.8 percent were positive for only IgM and IgA, respectively.

Seropositive participants were significantly more likely to report having had a case of COVID-19 in the household (p<0.001) and using public transport to get to work (p<0.05). Meanwhile regular use of face mask was significantly lower among seropositive participants (p=0.031). Nearly 15 percent of seropositive participants were asymptomatic throughout the study period.

In terms of immune memory, the researchers found detectable SARS-CoV-2-specific B- and T-cell responses in 20.7 percent and 35.0 percent of the representative subpopulation. Such memory was clearly correlated with seropositivity, though 17.2 percent of seronegative participants also demonstrated such responses.

“Assessment of IgM and T-cell responses may improve population-based estimations of SARS-CoV-2 infection. The pronounced surge of both symptomatic and asymptomatic infections among young adults indicates that the large-scale vaccination campaign should be continued,” the researchers said.