COVID-19 Household Transmission Risk After Prior Infection Differs by Age

Infection-induced immunity due to prior COVID-19 infection is associated with reduced infectivity in adults and adolescents but not children, suggesting children may play an important role in COVID-19 transmission dynamics. These study results were published in Clinical Infectious Diseases.

In this ongoing, community-based study, researchers assessed effects of prior infection-induced immunity among adults, adolescents, and children on the risk for household COVID-19 transmission. Respiratory samples were collected at days 0, 3, 7, 13, 21, and 30 from participants who tested positive for COVID-19 infection. Blood samples were obtainedtwice yearly and tested for COVID-19 anti-spike receptor binding domain immunoglobulin (Ig)G antibodies via enzyme-linked immunosorbent assay (ELISA). The researchers also tested vaccinated participants for IgG antibodies to the nucleocapsid (N) via ELISA. Pairwise survival models were used to estimate household secondary attack risk and rate ratios (RR).

Among participants included in the final analysis (n=975), 63.0% were women or girls, 30.1% were fully and 37.9% were partially vaccinated, and 90.5% tested positive for COVID-19 antibodies.

Transmission occurred in 70.2% of all households. Symptomatic vs asymptomatic participants were significantly more infectious (RR, 21.2; 95% CI, 7.4-60.7), and those with prior COVID-19 infection were significantly less likely to be reinfected compared with those naive to infection (RR, 0.52; 95% CI, 0.38-0.70).

After stratification by age, the researchers found that COVID-19 infectivity was significantly decreased among adults (secondary attack risk [SAR], 12.3; 95% CI, 10.3-14.8) and adolescents (SAR, 17.5; 95% CI, 14.8-20.7) but not children.

Although infection-induced immunity was associated with reduced household transmission risk in all age groups, this association was not significant among younger children (age range, 0-4 years). Of note, younger children infected with COVID-19 who were symptomatic vs asymptomatic did not differ in regard to the risk for transmitting the infection within the household.

Overall, children were less likely to transmit infection in the household, and the risk for transmission was lower in participants who were vs were not previously infected overall (RR, 0.52; 95% CI, 0.38-0.70). The researchers also noted that the risk for household transmission was lowest for participants who were infected within the past 6 months (SAR, 9.5; 95% CI, 6.3-14.1). However, a similar household transmission risk was observed among participants with any prior infection (SAR, 10.3; 95% CI, 8.8-12.0)  

Limitations of the study include misclassification bias and the lack of SARS-CoV-2 sequencing data for strain identification.

According to the researchers “We expect that as robust immunity develops globally through expanded vaccination efforts and repeat and breakthrough infections occur there will be a decrease in infectivity and lower rates of SARS-CoV-2 infections.”

Disclosure: One study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

This article originally appeared on Infectious Disease Advisor