Young children carry more virus – but seem to transmit less than adults or older children

Doug Hendrie

7/08/2020 1:17:55 PM

Children under five have far more SARS-CoV-2 in their nasopharynx, but do not transmit significantly in childcare or schools, according to new studies.

Young child with face mask
Children’s role in the transmission of the SARS-CoV-2 virus is not yet well understood.

It is now accepted that children are proportionately less likely to be infected with COVID-19 than adults.
But children’s role in transmission of the SARS-CoV-2 virus is less well understood, with new research offering potentially conflicting reports as to their impact on the spread of the disease.
One new study suggests that children under five may carry significantly more virus than adults, while other studies suggest that children are not major vectors for transmission.
On the transmission front, a new The Lancet Child & Adolescent Health observational study looked at real-world data from January to April, tracking COVID-19 spread within 25 schools and childcare centres in New South Wales.
The study found that 27 children or teachers went to school or childcare centres while infectious, but only an additional 18 people later became infected from 1448 contacts – a secondary attack rate of 1.2%.
This led the researchers to conclude that children ‘did not contribute significantly to COVID-19 transmission via attendance in educational settings’, when contact tracing and epidemic management is in place.
‘Our findings are the most comprehensive data that we have yet on SARS-CoV-2 transmission in schools and early years education settings,’ University of Sydney’s Professor Kristine Macartney, who is also Director of the National Centre for Immunisation Research and Surveillance, said.
Australian National University infectious diseases physician Professor Peter Collignon told newsGP the NSW study represents ‘good news’.
‘This showed that children who were infected did not seem to spread it much to others. They got it – they just didn’t seem to spread it,’ he said.
‘The important thing is that all of us would have thought children would be huge vehicles in spreading this, but the good news is they’re not. With many other diseases, children get it more and spread it more – like measles.
‘All the evidence I see is that this is very age-dependent. Children under 15 are much less of a factor in getting it and spreading it compared to 20 and 30-year-olds.
‘So children get it, but mainly when there’s a lot of community transmission, and they get it less often with less severe disease if they do get it. They probably get as much virus in their throats as an adult, but they may have fewer symptoms so they cough and sneeze less.
‘Most studies show children get it from an adult. So in schools, [transmission] is parents at the gate or teachers in the staffroom.’
Professor Collignon hopes the reason children under 15 are infected less is due to their relative lack of angiotensin converting enzyme (ACE)-2 receptors – not due to the immune system.
‘If it was due to an immune reaction, that would be a real worry because of the implications for vaccine immunity,’ he said.

According to the Department of Health, it is currently ‘not clear’ what role children play in the transmission of COVID-19.
In line with the NSW findings, a recent commentary published in Pediatrics concludes children ‘are not significant drivers’ of the pandemic.
Young children may have larger viral loads than adults
These latest findings have been complicated by new research in JAMA Pediatrics, which reports children aged under five may, in fact, be able to spread SARS-CoV-2 even more easily than adults.
That is based on the discovery that young children actually harbour much larger quantities of the viral nucleic acid in their upper respiratory tract compared to older individuals.
‘The observed differences in median CT [cycle threshold] values between young children and adults approximate a 10-fold to 100-fold greater amount of SARS-CoV-2 in the upper respiratory tract of young children,’ the researchers wrote.
To form their conclusions, researchers performed SARS-CoV-2 reverse transcriptase-polymerase chain reaction (PCR) on nasopharyngeal swabs taken from individuals in Chicago between 23 March and 27 April.
PCR amplification CT values were then recorded, with lower values indicating higher amounts of viral nucleic acid.
The researchers compared three groups who tested positive for SARS-CoV-2, with a total cohort of 145 patients with mild-to-moderate illness within one week of symptom onset.
Those groups were:
  • children younger than five (46 participants)
  • older children aged 6–17 (51)
  • adults aged 18–65 (48).
The researchers found similar median CT values for older children and adults, but young children had significantly lower median CT values, and therefore higher amounts of viral nucleic acid.
Stephen Kleid, an ENT and head and neck surgeon at Peter MacCallum Cancer Centre, told newsGP he was taken aback by these findings.
Even though it was a small study sample, Mr Kleid was particularly concerned about the amount of SARS-CoV-2 nucleic acid in young children’s upper respiratory tract compared to older individuals.
‘That’s a huge number, a marked difference,’ he said.
Mr Kleid was also surprised by researchers’ ability to efficiently swab the nasopharynx of such young children in the first place.
‘To take a swab from the nasopharynx, which in a child is back 5 cm, is a pretty impressive feat,’ he said.

The authors note their study is limited to detection of viral nucleic acid, rather than infectious virus. Even so, they say SARS-CoV-2 paediatric studies reported a correlation between higher nucleic acid levels and the ability to culture an infectious virus.
‘Thus, young children can potentially be important drivers of SARS-CoV-2 spread in the general population, as has been demonstrated with respiratory syncytial virus, where children with high viral loads are more likely to transmit,’ the authors wrote.
Mr Kleid also believes the increased viral load found within a young child’s nasopharynx indicates they could transmit the virus more.
‘The common sense answer is that children are the spreaders of it,’ he said. ‘That means they’re spreading it without getting sick.’
Mr Kleid says that fits in with spread of other infections among young children.
‘Who spreads colds and gastro to their parents? You ask mothers and teachers of children at creche and kinder, “What have you noticed since you’ve had a kid?” and they say, “I get a lot more colds”,’ he said.

ENT and head and neck surgeon Stephen Kleid believes children may be significant contributors to the spread of COVID-19.​
Mr Kleid says young children have a number of behavioural factors that result in their increased risk of transmitting infections, including their inability to practice proper hygiene or maintain distance from others.
He also explains that, as the SARS-CoV-2 virus resides in the goblet cells in nasal mucus, this may also contribute to children spreading the disease.
Anatomically, young children are more likely to have larger adenoids, which often obstruct nasal secretions from flowing down the back of their throats. These nasal secretions are therefore then emitted from the nose, and young children are unlikely to blow their nose, nor practice effective hand hygiene.
Considering those secretions can harbour a much higher amount of nucleic acid than in older individuals, Mr Kleid believes that is a real concern in terms of their ability to spread the virus.
The JAMA Pediatrics researchers also wrote that these factors ‘raise concern for SARS-CoV-2 amplification’ in that population.
While Mr Kleid is concerned that children aged under five may be significant spreaders of the virus, he is unable to explain the lack of infection rate in parents of these young children, and in teachers and caregivers of children aged under five.
‘It may be that the children are spreading it, they’re not getting sick, they’re carrying it, they’re spreading it to their mothers,’ he said.
‘Luckily, they’re not meant to be seeing their grandparents so they’re not spreading it to the older generation [who] gets symptoms.
‘Maybe that’s the answer.’
However, Mr Kleid does not know whether the virus has been affecting teachers and carers of young children more and, if not, why that is not happening.
A preprint non-peer-reviewed paper has reported similar findings to the JAMA Pediatrics study. That paper focused on contact tracing during phase one of the COVID-19 pandemic from March to April in the province of Trento, Italy.
It found the greatest risk of transmission to contacts was found for the cases aged under 15.
‘Although childhood contacts were less likely to become cases, children were more likely to infect household members, perhaps because of the difficulty of successfully isolating children in household settings,’ the authors wrote.
An outbreak of COVID-19 at a Georgia summer camp in the US also highlights the potential role of children as spreaders of the virus, as detailed in a paper published in Morbidity and Mortality Weekly Report on 31 July.
A total of 597 residents of Georgia attended that summer camp.
Test results were available for 344 attendees, with 260 found to be positive. Of the positive cases, 51% were aged 6–10, 44% were aged 11–17, and 33% were aged 18–21.
‘This investigation adds to the body of evidence demonstrating that children of all ages are susceptible to SARS-CoV-2 infection and, contrary to early reports, might play an important role in transmission,’ the researchers wrote. 
In light of the conflicting body of evidence, Mr Kleid believes more research is needed in order to clarify this issue.
For now, he remains concerned about the role of young children, spread of COVID-19, and its effect on the growing pandemic.
‘Maybe they’re the reason for the unknown spreaders,’ he said.
‘But who knows?’
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Dr Peter William Rankin   8/08/2020 3:02:56 PM

The weakness of the Lancet article in April is its claim that “only an additional 18 people were infected”. The missing phrase is “known”. Back then as we all remember Covid 19 testing was severely rationed to overseas travellers known close contacts and patients with symptoms. Brief contact as in childcare drop off and pick up was not then considered as an indication for testing. We have no idea how many contacts of this nature were infected but 18 is almost certainly an underestimation. Perhaps ten fold as some community serological testing has indicated. The vast majority of young Kids don’t get sick with Covid 19 but they do spread it. The reason why they have not been a large known source of community transmission is likely to be their absence of symptoms meaning the virus stays in their nasopharynx and they don’t cough or sneeze creating spread droplets or small particle aerosols which are the main way Covid 19 spreads. Measles is spread by aerosol so Kids are super spreaders.

Dr Anna Lindsay   15/08/2020 7:08:56 AM

A study out of Germany and in collaboration with the University of Cambridge found children to be just as infectious and capable of transmission of Covid as adults.