In a recent study posted to Research Square* and under review at Scientific Reports, researchers observed lower susceptibility of children and adolescents to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. 

Study: FamilyCoviDD19 Study: Lower SARS-CoV-2 transmission in children and adolescents compared to adults. Image Credit: Ground Picture/Shutterstock
Study: FamilyCoviDD19 Study: Lower SARS-CoV-2 transmission in children and adolescents compared to adults. Image Credit: Ground Picture/Shutterstock


Since the early coronavirus disease 2019 (COVID-19) pandemic, measures have been introduced to curb the spread of SARS-CoV-2. Children often develop asymptomatic or paucisymptomatic disease and have been assumed to spread the virus. Therefore, regular testing and school closures have been enforced. Moreover, this younger population has been deprived of societal participation due to rules that limit access to public places to the vaccinated or COVID-19-recovered subjects.

Reports suggest that social isolation affects the mental health of adolescents and children, elevating the risk of depression and anxiety. Therefore, there is a pressing need for safety measures that are highly effective and least restrictive to balance the containment of the COVID-19 pandemic and the mental health and education of children.

The study and findings

In the present study, researchers estimated seroprevalence in households to determine viral transmission rates. Families with at least one documented COVID-19 case were invited to participate in the FamilyCoviDD19 study. Blood samples were collected from participants, and data were obtained about demographics, COVID-19 (polymerase chain reaction [PCR]) testing, prior infection history, measures adopted during quarantine, and current health status. They enrolled 300 households, comprising 1056 individuals with a median household size of four.

Overall, 991 participants were included in the study with a median age of 33, and 341 subjects were < 18 years old. Of these, 950 individuals gave consent for blood sampling, and over 61% were seropositive. The authors defined an index case as the person with the highest probability of being the first one infected based on symptom onset, seropositivity, or positive test. Index cases were identified in 276 households, and 83% were found seropositive.

Comorbid individuals had higher odds of being seropositive and developing a symptomatic infection than those without comorbidities. In 27 households, no participant was seropositive; the index case was the only seropositive subject in 58 households, and all members in 112 households were seropositive. The odds of every member being seropositive were lower if the index case was < 18 years compared to households where the index case was aged 18 or above.

Similarly, the secondary attack rate (SAR) of younger index cases was lower than that of older index cases. Notably, the transmission of infection was more frequently observed from adult index cases to household members aged < 18 years than vice versa. Transmission from adolescents and children to underage and adult household members was less frequent. Significantly higher SAR was evident in households with a PCR-positive case than in the households where positive cases were serologically identified.

There was a greater likelihood that every member in the household of a symptomatic index case would be seropositive. Seropositivity was inversely related to the household size. As such, households with four or more members had a significantly lower probability of every member being seropositive than those with only two members. Interestingly, SAR in households that followed hygiene measures (room ventilation, using face masks, or social distancing) was comparable to those that did not.

A quarter of participants suffered from persistent symptoms (at blood sampling) when SARS-CoV-2 infection was less than 12 weeks ago. Seropositive subjects had higher odds of exhibiting persistent symptoms when the infection within the household occurred < or ≥ 12 weeks ago than seronegative participants. Likewise, individuals who developed symptoms during acute infection were more likely to experience persistent symptoms than asymptomatic cases at < or ≥ 12 weeks after infection within the household.

Further, adolescents and children were less likely to develop persistent symptoms than adults. The probability of persistent symptoms correlated with gender but not age. Females were more likely to present with persistent symptoms 12 weeks after infection than males. Comorbid individuals were more likely to suffer from ongoing symptoms after infection than those without comorbidities.


The current study evaluated SARS-CoV-2 transmission in households with a confirmed index case. More than 61% of the household members were seropositive after infection within the household, higher than previous estimates from January 2021. Nevertheless, the incident rate was the same among children and adults. Most SARS-CoV-2 infections were introduced by adults into the household than children/adolescents, given that only 16.3% of index cases were < 18 years old.

In summary, the study noted that younger individuals (< 18 years) had a milder disease and were less susceptible to infection, with lower odds of transmitting the infection to household members. The authors suggested that pandemic control should be focused more on adults than adolescents and children.

*Important notice

Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.


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