A leading Australasian public health expert says New Zealand is taking "a calculated risk" in reopening schools and early childhood centres next week.
Professor Tony Blakely, a former Otago University professor who now heads the Population Interventions Unit at Melbourne University, says scientists still don't know how much children transmit Covid-19 to other children and adults.
"Opening schools – just to the children of parents going back to work in the workplace - may be a necessary and welcomed step. But it is a calculated risk," he said.
Director-General of Health Dr Ashley Bloomfield yesterday defended the decision to reopen schools and early childhood services from April 29 on the basis that children "have low infection rates, don't become unwell, and don't pass on the virus to adults".
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International data confirms that children are much less likely than adults to be detected with the virus, and even less likely to die from it.
The World Health Organisation found that no children under 10 died in China, South Korea, Italy or Spain, and no young people aged 10 to 19 died in any of those countries except China, where the death rate among young people who caught the disease was only 0.2 per cent.
However, a paper published by Johns Hopkins University on April 17 said it was "still not known what role children play in the transmission of [Covid-19]".
"There has been some evidence that Covid-19 produces more mild illness in children and therefore it may be less likely to be detected than in adults," the paper said.
"However, without more conclusive evidence, it is difficult to quantify the role of children
in propagating Covid-19 to other students, their family members, teachers, and school
"Furthermore, schools and childcare facilities are staffed by adults, some of whom
may be at risk of severe illness. These considerations weigh against reopening."
Blakely said the true infection rate of Covid-19 among children was almost certainly higher than the reported number of cases, because most children who get the virus don't show the usual symptoms such as coughing and breathing problems.
But he said no one knew the rate at which children were passing on the virus to others.
"It is possible that transmission of Covid-19 between children is very low or even negligible, mirroring the low rate of clinical sequelae among children – but we do not know how low.
"It is possible that NZ's elimination goal will be undermined by opening schools, if in doing so a low rate of transmission is allowed that would otherwise not occur.
"Moreover, because children are generally asymptomatic, any school transmission will be harder to detect, yet allow infection to be spread between otherwise unconnected households – propagating ongoing society-wide transmission.
"On the other hand, life and society needs to get back to normal where possible. Opening schools – just to the children of parents going back to work in the workplace - may be a necessary and welcomed step. But it is a calculated risk."
He said two things needed to be done to reduce the risk:
• "Access as early as possible emerging international research on the transmissibility of Covid-19 among children [it is poorly understood at the moment] – and tweak the policy accordingly and rapidly."
• Offset the risk of school openings (and other loosening of restrictions) with extremely thorough surveillance, contact tracing (including apps) and testing (continuing of contacts of infected and quarantined cases, but rolled out further to people with possible symptoms of Covid-19 and population surveys).
"If any new cases seem to have arisen due to transmission in schools, consider either closing schools again, or pivoting away from an elimination goal to a suppression or 'controlled adaptation to the virus' goal."
The Early Childhood Council, NZ Educational Institute and the Herald have asked the Ministry of Health to release the basis of Bloomfield's advice on reopening schools and early childhood services.
• Level 3 rules for education: covid19.govt.nz.