Latest evidence on impacts of COVID-19 in children: March 2021

This article discusses the latest evidence describing how COVID-19 affects children, and the role that children have in the transmission of the virus in the population. This is a complex interplay between how susceptible children are, how infectious they are, the proportion of children in a population, and how they mix with other age groups. This is relevant to implementing and lifting public health measures that seek to limit transmission by children. It is also important in determining how best to reimpose restrictions that involve educational settings in order to minimise subsequent local outbreaks of disease.

COVID-19 infections in children

Children of all ages, including newborns, can be infected by the SARS-CoV-2 virus, but infections are milder, with children much less likely to have symptomatic disease than any other age group. Large studies in multiple countries consistently show that children under the age of 18 years consistently account for fewer than 2% of all infections detected. Fewer than 1% of children will develop severe or life-threatening disease, with death a rare outcome. The data so far show that the likelihood of being infected and developing clinical disease follows an age gradient, where the risk of being infected increases with age. There is good evidence that younger children (pre-school and primary age) are less susceptible to infection than older children. There is high confidence that children and young people (aged under 19 years) are much less susceptible to developing what is termed clinical disease (having recognised signs and symptoms of COVID-19).

A similar age gradient is also seen in mortality data for COVID-19, with very few deaths in children. UK data are discussed below. Studies that have looked across age groups report that teenagers are more susceptible to infection than younger children.

Studies that test large numbers of people to see what proportion have antibodies to SARS-CoV-2 report that only half of children who had an infection experienced symptoms. The reasons why children are less likely to have symptomatic infections are not yet fully understood but it is thought to be related to the expression of the specialised protein (called a receptor) in the body to which the SARS-CoV-2 virus binds. The expression of this receptor increases with age.

New variants of the virus and infections in children

The Scientific Advisory Group for Emergencies (SAGE) has reviewed the limited data available on how infection cause by new variants of the virus might affect children. There is nothing to suggest that the B1.1.7 variant affects any particular age group differently. This variant accounted for up to 70% of overall infections in London in January 2021. So far there is insufficient evidence to determine if the B1.1.7 variant causes more severe infections in children, but there have been no signals to indicate this in the national data reported so far.

Long COVID and children

Some people who have had a COVID-19 infection continue to experience ongoing symptoms or other complications for weeks or months after the initial infection, referred to as long COVID. You can read more about this in our article about the short and long-term effects of COVID-19. The Office for National Statistics has published a paper with experimental estimates about what proportion of the population have symptoms of long COVID. This research uses methods that are in development. Data show that persistent symptoms are less common in children than adults. Between 10–18% of children aged 2–16 years had symptoms 5 weeks after a positive test for the virus. This preliminary data and study design limit the strength of conclusions that can be drawn, so larger well-designed studies are needed to clarify what this means for children in the long-term. Research on this theme will also inform decisions about including children in future vaccination programmes.

UK data on COVID-19 in children

The UK has paediatric surveillance programmes for COVID-19. In the UK, daily updates are published on the Government’s COVID-19 data dashboard – these data detail cases by age group but not deaths by age group. These data are collected and reported by Public Health England, which publishes a detailed weekly bulletin about COVID-19, with equivalent releases produced by agencies in the rest of the UK (Northern Ireland, Scotland, Wales). The latest data in the figure below shows how COVID-19 case rates differ between age groups for both sexes.

The Office for National Statistics publishes weekly data on COVID-19 mortality in England and Wales, with equivalent data published by National Records Scotland and the Northern Ireland Statistics and Research Agency. There are differences in how deaths are reported between national statistics authorities, public health bodies and government departments. The ONS reconciles all mortality data across the UK and publishes this periodically. The UK Government data dashboard reports the deaths of people who had tested positive, but not all deaths recorded will have been officially registered at that point. The ONS and devolved equivalents report registered deaths where COVID-19 is mentioned on the death certificate.

Provisional ONS data on COVID-19 deaths have been published weekly since the first UK COVID-19 deaths were registered in March 2020. The latest ONS data published on 2 March 2021 report that, since the pandemic began, there have been:

• 2 deaths in children aged 1 year and under.
• 1 death in children aged 1–4 years old.
• 3 deaths in children aged 5–9 years old.
• 6 deaths in children aged 10–14 years old.
• 20 deaths in children aged 15–19 years old.

As of 5pm on 4 March the Government data dashboard reports the total number of deaths with COVID-19 on the death certificate for all age groups in the UK at 140,062.

Clinical outcomes for children

Children tend to experience milder symptoms than adults or have no symptoms at all (asymptomatic). The pattern of symptoms also differs, for example, children are less likely to have a fever, cough and shortness of breath than adults, but are more likely to experience gastrointestinal symptoms and vomiting. Children usually recover within 1–2 weeks. A detailed review article on  the characteristics of COVID-19 in children outlines the results from numerous international studies about how the disease affects this age group.

Very few children develop severe disease. The risk of a child dying from COVID-19 is extremely low, with a current estimate of mortality of 0.01%. This means one death for every 10,000 cases.

A rare outcome for some children with COVID-19 is a severe inflammatory syndrome (Paediatric Inflammatory Multisystem Syndrome Temporally associated with SARS-CoV-2, PIMS-TS) which was recorded in the first wave of the pandemic. Work to coordinate research and clinical treatment has been guided internationally by the World Health Organization that published a scientific brief on the topic, and in the UK by medical bodies focused on the care of children. These include the National Institute for Health and Care Excellence (NICE), the UK Paediatric Critical Care Society and the Royal College of Paediatrics and Child Health; all of whom are contributing to clinical guidance for health professionals.

Children at risk of severe outcomes

There are some data on whether children with underlying medical conditions are at greater risk. Five studies looking at paediatric cases have indicated that having a weakened immune system does not significantly increase the risk of developing severe disease. However, researchers expect that children with cardiovascular or respiratory disease, or who are immunosuppressed as a result of medical treatment (such as for some cancers), may be more vulnerable. This is reflected in some research data that looked at whether children admitted to hospital with COVID-19 had other medical problems.

Studies in Italy, China and the US have found that more children with other health problems were hospitalised, although this wasn’t necessarily linked to having more serious disease, apart from in infants aged under 12 months. The Royal College of Paediatrics and Child Health has published some guidance on which groups of children should be advised to shield. Each national government and health service has advice on shielding and which groups this applies to. Shielding for children means that they must stay at home and not attend school or college.

There are some limited data suggesting that children from ethnic minority backgrounds may be at increased risk of having severe COVID-19 disease. An increased risk for adults from ethnic minority backgrounds is summarised in two reports by Public Health England, one on overall disparities in risks and outcomes and another focusing on the impact on Black, Asian and Minority Ethnic groups. Subsequent work is investigating disparities in more detail, so that measures to address them are put in place. The main disparities are that people from ethnic minorities are more likely to test positive for COVID-19 than White ethnic groups and more likely to die. Adults are also more likely to have a job associated with higher COVID-deaths. There are fewer data about disparities in outcomes for children, but this is an active area of research.

A study of children with COVID-19 in UK hospitals reported that those from a Black background were more likely to need critical care. Another finding suggested that children with Black ethnicity were over-represented (10% of children in the study compared with 4.7% of children in the population). It is unclear whether this is related to the ethnic diversity of the populations served by the hospitals in the study.

These echo results from previous studies featured in our last article on children which highlight an association between the risk of severe disease and non-White ethnicity. Much larger studies are needed in order to draw firm conclusions about any increased risk, what the magnitude of the risk might be, and how it might differ between ethnic groups and in comparison with adults.

Transmission of COVID-19 by children

Understanding the role that children play in transmitting the virus is of significant policy relevance, since measures have been taken to limit the opportunities for transmission in the settings where children mix with other children and adults. Policies to address this have been school closures and other steps to minimise the risk of transmission in educational settings, alongside other wider population-level restrictions. Research can also inform whether, when and how measures can be reversed or modified. Information about transmission is also critical in designing population immunisation programmes.

The extent to which children transmit the virus is not yet fully understood and is complicated by the fact that asymptomatic cases are common in children. One concern has been whether viral shedding by infected children with no symptoms is driving viral transmission, particularly between homes and schools. An evidence summary by the Royal College of Paediatrics and Child Health based on multiple studies indicate that children are less likely to introduce the virus into their households than adults, with other data suggesting that onward transmission between children at school is limited. Public Health England conducted a large study of infection and transmission in schools in June 2020. The report found that infections were more common in staff than pupils, with most outbreaks linked to staff rather than children, and  were more likely to occur in regions in which infection prevalence was high. A similar study in schools in November 2020 found that infection rates among pupils and staff were also linked to those found in the wider community. While infections do occur in education schools, they do not appear to be a driving force for transmission. SAGE recently published a review of the latest evidence about infections in children and schools. It states that school openings do contribute to an increase in transmission, possibly through increasing adult contacts as parents and carers return to their workplace, but some of the risk can be mitigated. Controlling viral transmission in the community also protects schools.

Immunising children against COVID-19

Children are not included in the national COVID-19 vaccination programme for which priority groups of adults have already been announced. The JCVI has recommended that some older children who are at high risk of exposure or of serious outcomes be offered the Pfizer/BioNTech or the AstraZeneca vaccine. This advice would refer to, for example, older children with severe neuro-disabilities. Decision about whether a child should be immunised should be based on a discussion of the risk and benefits with a doctor.

There is limited research about COVID-19 vaccination in children, although new studies will examine how well vaccines work in this group. The University of Oxford will run a National Institute for Health Research (NIHR) funded study of the AstraZeneca vaccine in children aged 6­-17 years. This will reveal how children’s immune systems respond to the vaccine and give important safety data. As the body of evidence about the use of vaccines accumulates, the JCVI will update its advice on national immunisation strategies.

Further reading

The Royal College of Paediatrics and Child Health has published an evidence summary of various aspects of COVID-19 and children which is updated regularly.

COVID-19 in Children, UK Research and Innovation

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