The frequency of children carrying asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been suggested to be higher than among adults. It is also suggested that asymptomatic children enhance viral spread. A research letter by published in the journal JAMA Pediatrics in September 2020 explores the truth of this common belief.
Earlier studies have shown that both children and adults have a similar prevalence of COVID-19, as observed by antibody testing. According to research carried out at SJD Barcelona Children’s Hospital, 17% of children who came into contact with a case of COVID-19 became infected. This is similar to the ~19% of adults who became infected following household contact. More than 99% of infected children had no or mild symptoms, unlike the higher percentage of infected adults who show moderate to severe symptoms.
Viral carriage in the throat at one month after the first case of COVID-19 at home was detected in a third of adults, and just over a tenth of children, but at very low levels.
Another paper published by the American Academy of Pediatrics shows that asymptomatic and mild illness is demonstrated in about 4% and 51% of infected children. One researcher said, “Asymptomatic shedding is actually probably more likely to perpetuate an epidemic within a population.”
The putative role of children in the asymptomatic transmission of COVID-19 has shaped public health decisions, including school closures.
Lower Frequency Among Children
Carlo Agostoni, M.D., of Fondazione IRCCS, Ca’ Granda Ospedale Maggiore Policlinico in Milan, Italy, and colleagues examined the frequency with which this phenomenon occurred among children.
The study tested children and adults admitted with non-infectious conditions but not having any clinical features of SARS-CoV-2 infection to understand the relative frequency of asymptomatic transmission in these two groups of hospitalized patients.
All patients in this group were tested immediately after admission with nasopharyngeal swab testing, irrespective of symptoms. An initial negative swab led to a second one within 12-48 hours. No patient on admission had signs or symptoms of COVID-19 or a history of prolonged or close contact with COVID-19 cases for at least 21 days preceding their admission.
There were 83 children in the study, with a median age of 5 years. The number of adult patients in the study was 131, with the median age being 77 years. Only ~1% of children tested positive, compared to ~9% in adults. In fact, of the 12 adults with a positive RT PCR test, 11 required only one swab test. None of them had any symptoms or signs of infection over the next 48 hours.
This means that the risk of asymptomatic infection among children is almost 90% lower than in adults.
It is notable that in this study, which was carried out in Milan, where the viral burden is among the highest in the world, 9% of adults admitted to hospital for reasons other than any infection were positive for SARS-CoV-2. In contrast, only 1% of hospitalized children were positive.
Children Are Not More Infectious than Adults
Overall, earlier research shows that about 80% of adults have asymptomatic COVID-19 infection. Most reports on asymptomatic infection in children are from China and indicate they make up about 15% of infected cases. The current study supports the markedly lower prevalence of asymptomatic infection among children compared to adults. This means that they probably do not play a significant role in the viral spread that has been attributed to them.
This was a retrospective study conducted at a single center. Only hospitalized cases were analyzed. Thus, these findings are only preliminary. However, they do contribute to a better understanding of the epidemiology of this disease and show that there is limited evidence that children carry the infection asymptomatically at higher rates than adults.