Children can mount strongest COVID-19 immune response without infections

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In a new study, researchers found that children in a Melbourne family developed a COVID-19 immune response after chronic exposure to the SARS-CoV-2 virus from their parents.

They found that despite close contact with symptomatic infected parents, including one child sharing the parents’ bed, the children repeatedly tested negative for COVID-19 and displayed no or minor symptoms.

The research was conducted by a team at the Murdoch Children’s Research Institute (MCRI).

Compared to adults, children with COVID-19 usually have a very mild or asymptomatic infection, but the underlying differences between children’s and adults’ immune responses to the virus remained unclear.

In the study, the team looked at the immune profile in a Melbourne family of two parents with symptomatic COVID-19 and their three primary school-aged children.

Before COVID-19 took hold in Australia, the parents attended an interstate wedding without their children.

After returning, they developed a cough, congested nose, fever and headache, and all family members were immediately recruited for the research study.

Samples including blood, saliva, nose and throat swabs, stools, and urine were collected from the family every 2-3 days.

The researchers found COVID-19 specific antibodies in the saliva of all family members and in detailed serology testing compared to healthy controls.

The team performed a careful analysis of the various subsets of immune cells and antibody types, showing that the children mounted an immune response that potentially contained the virus.

The youngest child, who showed no symptoms at all, had the strongest antibody response.

The team says despite the active immune cell response in all children, levels of cytokines, molecular messengers in the blood that can trigger an inflammatory reaction, remained low.

This was consistent with their mild or no symptoms.

While all family members fully recovered without requiring medical care, the team, unfortunately, could still not be certain how long, if at all, they would be protected from reinfection.

This study raised the possibility that despite chronic exposure, children’s immune systems allowed them to effectively stop the virus from replicating inside their cells.

One author of the study is MCRI’s Dr. Shidan Tosif.

The study is published in Nature Communications.

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