Coronavirus: Children can carry larger amounts of virus than adults - yet show no symptoms
Children can carry larger amounts of the virus than adults left fighting for their lives - yet show no symptoms, say scientists.
This means they could be particularly contagious to family members - such as vulnerable grannies and grandads, warn scientists.
The findings are based on nose, throat and blood samples from almost 200 young paediatric patients in the US.
Lead author Dr Lael Yonker, of Massachusetts General Hospital, said: "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. You think of a hospital, and of all of the precautions taken to treat severely ill adults.
"But the viral loads of these hospitalised patients are significantly lower than a 'healthy child' who is walking around with a high SARS-CoV-2 viral load."(Image: Getty Images)
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Even when children exhibit symptoms like fever, runny nose and cough, they often overlap with flu and the common cold.
This confounds an accurate diagnosis of Covid-19, the illness derived from the SARS-CoV-2 coronavirus, she said.
The study published in the Journal of Pediatrics shows children may play a greater role in the pandemic than feared.
It is the most comprehensive of its kind to date - involving 192 infants, children, adoescnts and young adults up to the age of 22.
Overall, more than a quarter (49) tested positive for SARS-CoV-2 - and another 18 had late-onset, Covid-19-related illness.
The infected participants were found to have to have a significantly higher level of virus in their airways than adults - fighting for their lives in intensive care units.
The study also examined antibody responses in healthy children and those with Covid-19 or linked organ disorders called Multisystem Inflammatory Syndrome (MIS-C).
It carries implications for the reopening of schools, daycare centres and other locations with a high number of children and close interaction with teachers and staff.(Image: Getty Images)
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Senior author professor Alessio Fasano, a world renowned paediatrician at Massachusetts, said: "Kids are not immune from this infection, and their symptoms don't correlate with exposure and infection.
"During this Covid-19 pandemic, we have mainly screened symptomatic subjects, so we have reached the erroneous conclusion the vast majority of people infected are adults.
"However, our results show kids are not protected against this virus. We should not discount children as potential spreaders for this virus."
The researchers pointed out children with Covid-19 are not as likely to become seriously ill as adults.
But as asymptomatic carriers attending school, they can spread infection and bring the virus into their homes.
This is a particular concern for families in certain socio-economic groups, which have been harder hit in the pandemic.
It also applies to and multi-generational families with vulnerable older adults in the same household.
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In the study, half (51%) of children with Covid-19 came from low-income communities - compared to two percent from high-income.
And although younger children have lower numbers of the virus receptor than older peers and adults, this does not correlate with a decreased viral load.
The researchers said MIS-C is potentially life-threatening. It can develop in children several weeks after infection.
It can lead to severe cardiac problems, shock and acute heart failure.
Prof Fasano said: "This 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 with these very serious systemic complications, the heart seems to be the favourite organ targeted by post-Covid-19 immune response."
Understanding these immune responses is critical for developing drugs and vaccines, said Dr Yonker.
Her team is constantly fielding questions from parents about the safe return of their children to school and daycare.Video Loading Video Unavailable The video will start in8Cancel Play now
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They agree the most critical question is what steps the schools will implement "to keep the kids, teachers, and personnel safe."
Recommendations from their study include not relying on body temperature or symptom monitoring to identify infection in the school setting.
They underline the importance of social distancing, universal mask use, effective hand-washing protocols and a combination of remote and in-person learning.
They said routine and continued screening of all students with timely reporting of the results are an imperative part of a safe return-to-school policy.
Prof Fasano said: "This study provides much-needed facts for policymakers to make the best decisions possible for schools, daycare centers and other institutions that serve children.
"Kids are a possible source of spreading this virus, and this should be taken into account in the planning stages for reopening schools."
He fears a hurried return to school without proper planning could result in an uptick in cases of COVID-19 infections.
The researchers said: "If schools were to re-open fully without necessary precautions, it is likely children will play a larger role in this pandemic."