There are a number of different aspects to consider with regard to SARS COV-2 and its impact on different age groups; transmission rate, the likelihood of infection and the severity of the disease/death rate. The graph below looks at the split by age and gender of total cases in the UK as of July 26th.
Nature Medicine published a paper of a study by the London School of Hygiene and Tropical Medicine which concluded that those under 20 are approximately half as susceptible to COVID-19 compared to those over20 years of age. It also estimates that symptoms appear in 21% of infections among 10- to 19-year-old people and this increases to 69% in adults over 70.
The study looked at demographic data from 32 locations in six countries ― China, Italy, Japan, Singapore, Canada and South Korea ― and data from five published studies on estimated infection rates and symptom severity across different age groups. They then used an age structured mathematical model on this data to estimate disease susceptibility and symptoms by age to try and understand why there was a low number of reported cases in the younger age groups. The results showed:
The model found that younger age groups were less susceptible to COVID-19 . This decreased susceptibility could come from protection from prior exposure to other cornaviruses or from other respiratory viruses as children experience these more frequently than adults. However it should be noted that direct evidence for th decreased susceptibility has been mixed.
Mild or no symptoms
The study found that children could experience mild or no symptoms more frequently than adults. This would result in a lower number of reported cases, however, children with mild symptoms or those who are asymptomatic could still be capable of transmitting the virus, potentially at a lower rate than those who have more severe symptoms, this was the case for flu.
Children tend to make more social contacts than adults and so this will contribute to the rate of transmission. This higher contact rate is why school closures are considered as a means of control for governments, but its impact will depend on the rate of transmission. This will also depend on the fraction of the population that are children, the contact they have with other age groups and their level of infectiousness.
The researchers say that further research is needed to determine the transmissibility of asymptomatic infections or infections with mild symptoms in order to effectively forecast and control COVID-19 epidemics.
Even though studies, such as the one above, seem to suggest that children
do not transmit the virus as much as adults, scientists still cannot say for
sure and the evidence is still evolving.
In Australia a New South Wales government report found no student to
teacher transmission and very low student to student transmission.
Conversely in the state of Victoria, the chief health officer suggested that
transmission amongst the older teens is responsible for a large cluster of
cases at Al-Taqwa College. The school was closed on 29thJune when a
positive test was confirmed.
All 2,000 students and 300 staff were told to isolate and get tested and the number of cases linked to the school grew to 102, which was the states second largest outbreak. He said that the cluster involved significant student to student transmission particularly in the older year groups. He said that this group tend to have more transmission and do not social distance as adults would.
An epidemiologist and infectious disease expert at the university of New South Wales said that schools should consider making masks mandatory in classrooms as older students are respond to the disease and transmit similar to adults and in the winter when windows are closed and rooms poorly ventilated it is difficult to remove particles that are suspended in the air even for a short time. She said that this age group needed to be reminded that close contact with each other at school for many hours can produce infection which can then be spread within a family and their wider connections.
A recent study from South Korea found that within the home 10-19 year old children transmit the virus as much as adults whereas with those under 10 it was less. In addition, a recent study from Israel found that an outbreak at a secondary school there were overcrowded classrooms, lack of mask wearing and air conditioning which were all likely to be contributory factors.
Current School Covid Requirements
Japan, SouthKorea, Taiwan and Vietnam have implemented fever screening. THE US CSC recommends that parents check their child's temperature before and on arrival at school. Although non contact infrared thermometers may not e that reliable they are a reminder to parents, staff and student about the risks.
France, Belgium , Germany and Israel have differing requirements for the use of face masks among students and teachers.
Severity of Disease/Death
The graph below shows the death rate by age in the US from January 2nd to 11th July showing that age clearly affects mortality rates.
Older people have a weaker immune system making them more vulnerable to infections. When they are infected there is higher chance of a cytokine storm where the immune system overreacts and produces too many chemicals to fight infections. This causes severe inflammatory reaction which could cause damage to the body including organ failure.
In addition, older people are more likely to have an underlying condition which also increases the risk of a severe reaction to SARS COV-2.