SARS-CoV-2 viral load

In a comprehensive study, researchers reported that children carry a higher SARS-CoV-2 viral load and could potentially be more highly contagious, even when asymptomatic.

As the COVID-19 pandemic gripped the world, one positive highlight was that the SARS-CoV2 virus appeared to spare children. As compared to adults, fewer children were reported to be infected and need hospitalization due to the SARS-CoV2 virus. However, a study of 192 children showed that while children might appear asymptomatic or suffer from mild symptoms, they have a high SARS-CoV-2 viral load. The high viral load means that they could spread the infection to their family members and others who are in close proximity.

The study included children who reported sick to urgent care clinics or were hospitalized due to confirmed or suspected SARS-CoV2 infection. It also included children suffering from Multi-System Inflammatory Syndrome (MIS-C), an inflammatory disease that affects different parts of the body and is thought to be associated with COVID-19. The study was published in the Journal of Pediatrics.

Of the 192 children, 49 tested positive for SARS-CoV2, and an additional 18 children were diagnosed with MIS-C. While the study included children between the ages of 0 to 22 years, 34% or 16 children with SARS-CoV2 infection were between the ages of 11 to 16 years. Children with MIS-C were younger with 39% or 7 children between the ages of 1 to 4 years.

Most of the children reported symptoms that were common with other illnesses such as influenza or the common cold. Children with or without the SARS-CoV2 infection reported fever, cough, congestion, runny nose, and headache. This can make a diagnosis based on symptoms alone quite difficult. Loss of smell and sore throat were few distinguishing symptoms of SARS-CoV2 infection.

The findings from the nose and throat swabs as well as blood samples of these children revealed a high viral load in the early days of infection. The viral load observed in these infected children was comparable to viral load in adults who needed intubation due to COVID-19. Even during the asymptomatic phase of the infection, the viral load in infected children was higher than in hospitalized adults who showed symptoms for over a week. As Dr Lael Yonker, director of the MGH Systic Fibrosis Center and lead author of the study described, “I was surprised by the high levels of virus we found in children of all ages, especially in the first two days of infection. I was not expecting the viral load to be so high. …, but the viral loads of these hospitalized [adult] patients are significantly lower than a “healthy child” who is walking around with a high SARS-CoV2 viral load.”

Along with viral load, the researchers also studied the gene expression of the ACE2 receptor which binds to the SARS-CoV2 virus. Their study found that while ACE2 expression was higher in infected children as compared to those uninfected, there was no correlation between viral load and ACE2 expression. This suggests that once infected, children can carry a high viral load irrespective of ACE2 levels, suggesting that even regardless of their own susceptibility to developing COVID-19, children could be more contagious. Additionally, the researchers found that ACE2 expression levels increased with age and high ACE2 levels could predispose some children to infection.

The researchers also found that the immune response is accelerated in children with MIS-C and this could cause complications, including heart failure. MIS-C is an infection affecting multiple organs that can develop in children with COVID-19 several weeks after infection. As Dr Fasano explains, “This [MIS-C] is a severe complication as a result of the immune response to COVID-19 infection and the number of these patients is growing. And, as in adults…, the heart seems to be the favourite organ targeted by post-COVID-19 immune response.”

More than a quarter (27% or 3 out of 11) of the asymptomatic children who were suspected of exposure to the virus tested positive. Of the infected children, nine children did not have any known exposure to the virus. Half of the number of children with acute infection attended grade school.

These results have implications for the reopening of schools and daycare centres where children are in close contact with other children and adults like teachers. As Dr. Alessio Fasano, director of the Mucosal Immunology and Biology Research Center at MGH and senior author of the paper explained, “During this COVID-19 pandemic, we have mainly screened symptomatic subjects, so we have reached the erroneous conclusion that the vast majority of people infected are adults. However, our results show that kids are not protected against this virus. We should not discount children as potential spreaders for this virus.”

Given that a significantly larger number of children (51% or 25 children) with SARS-CoV2 infection came from lower-income households, it is particularly concerning for the families of these children who most likely live in multi-generational households, increasing the risk of infecting vulnerable older adults, such as their grandparents.

The implications of children as carriers of infection are serious. The authors of this study make several recommendations to ensure a safe reopening of schools and other centres. They believe that continuous and routine screening of all students irrespective of the presence of symptoms and timely reporting of these results is crucial to a safe return of students to schools. Additionally, social distancing, effective hand-washing, universal mask use, and a combination of remote and in-person learning are essential and prudent methods to combat the spread of SARS-CoV2 infection.

Written by Bhavana Achary, PhD

References:

Original study – Yonker LM, Neilan AM, Bartsch Y, et al. Pediatric SARS-CoV-2: Clinical Presentation, Infectivity, and Immune Responses [published online ahead of print, 2020 Aug 18]. J Pediatr. 2020;S0022-3476(20)31023-4. doi:10.1016/j.jpeds.2020.08.037 https://www.jpeds.com/article/S0022-3476(20)31023-4/fulltext#secsectitle0025

Press Release- https://www.eurekalert.org/pub_releases/2020-08/mgh-rsc081720.php 

Image by chiplanay from Pixabay 

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