COVID-19 vaccines have been deployed in the UK since December 2020. This article examines the impact of COVID-19 vaccines on transmission of the virus. It also considers the potential implications of vaccine-induced protection for easing lockdown restrictions and debate about potential introduction of immunity certification or a vaccine passport scheme.
- There is very good evidence that children who have COVID-19 are much less likely to develop severe symptoms and much less likely to die from the disease than people in older age groups.
- There is good evidence that children under 13 years old are less susceptible to developing clinical disease (this means having recognisable signs and symptoms) than adults. It is not yet clear whether this is also the case for older children.
- There is some research indicating that children aged 13 years and under may be less susceptible to infection than adults, but the confidence in this evidence is low. There is insufficient research to say whether this is the case for older children.
- There is some evidence to suggest that children transmit the virus less than adults, but more research is needed to reduce uncertainty.
- Children are more likely to catch an infection from adult(s) in their household.
- There is evidence that schools are a low-risk environment for transmission.
- There are some limited data suggesting that children from a black, Asian or minority ethnic background may be at higher risk of severe disease, consistent with evidence for adults. Large and well-designed studies are needed in order to draw firm conclusions.
- Pregnant women are not more likely to contract the virus. Transmission of the virus from mothers to babies is low. Some babies born to SARS-CoV-2 positive mothers will develop an infection; these babies are not at increased risk of severe disease.
- This is part of our rapid response content on COVID-19. You can view all our reporting on this topic under COVID-19.
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.
Prevalence in children
Children of all ages, including newborns, can be infected by the SARS-CoV-2 virus. There is some evidence suggesting that younger children are less susceptible to infection than adults. It is not clear whether older children differ in their susceptibility to infection compared with adults. In the earliest stages of the outbreak, epidemiological studies of disease clusters reported that severe infections were more common in adults than children. It was not possible at that early stage to know whether children were less likely to catch the virus, or be less likely to have symptoms, or both, and how they might be involved in transmission. The World Health Organization’s (WHO) report of the WHO-China joint mission on COVID-19, which was published in late February, confirmed the emerging pattern that children accounted for a very small proportion (2.4%) of all reported cases at that time. In its meetings with Chinese officials and experts, the WHO team was also told that there were no known cases where transmission was from a child to an adult. Subsequent studies in multiple countries involving larger samples of people of all ages consistently show that children under the age of 18 account for less than 2% of all infections detected. As the pandemic has progressed, researchers have examined how the virus affects children; these studies are used to inform clinical practice and policy-making.
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.
Initial studies looked at the various characteristics of people who had tested positive for COVID-19, including age and sex. A study of the first 7,755 confirmed cases in South Korea reported 75 cases in 0–9 year olds, and 405 cases in 10–19 year olds. There were no deaths in either group.
Another approach is to test whole communities or a large sample of people who are representative of the whole population. This is an important method since it will also detect people who test positive but are asymptomatic. A study in Vo’, Italy analysed how lockdown impacted transmission in the community. Of the 234 children aged 0–10 years tested, none were found to be positive for the virus. Some of these children were living with family members infected with the virus. A much larger population screening study in Iceland tested 9,199 people representing 6% of the population. The study was split into two main parts:
- Testing targeted at people at high-risk for infection (being symptomatic, contact with a known case, or recent travel to high-risk countries).
- General population testing.
Children under 10 years old were less likely to test positive than other age groups, and the percentage infected increased with age. For the targeted testing group, 6.7% of under 10s tested positive compared with 13.7% for all people over 10 years old. For the general testing, no children under 10 tested positive, compared with 0.8% of those over 10 years old.
A Spanish study commissioned by the Ministry of Health looked for COVID-19 antibodies in a large population sample of 60,897 people between 27 April and 11 May. A scientific report of these data was published in The Lancet. The sample included 35,883 households and was representative of the overall population. It found that overall, 5.0% of the sample had antibodies against SARS-CoV-2, with no differences between males and females. At least one-third of people who had antibodies had not had any symptoms. The percentage of children who had antibodies against SARS-CoV-2 was lower than in adults, and shows an age gradient:
- 1.1% in under 1 year olds.
- 2.2% in 1–4 year olds.
- 3.0% in 5–9 year olds.
- 3.9% in 10–14 year olds.
- 3.8% in 15–19 year olds.
A similar age gradient is also seen in mortality data for COVID-19, with very few deaths in children. UK data are discussed below.
There are some data showing that there are more cases in male children than females; this is also the case for adults. There are no clear answers yet as to why this is the case, but scientists have speculated that this is likely to reflect a combination of biological mechanisms and behavioural differences (the latter particularly for adults). Females tend to have a more effective immune response making them more resilient to infectious disease. This is thought to derive from the large number of immune genes on the X chromosome (females have two X chromosomes).
UK data on COVID-19
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 from Public Health England show the age gradient for confirmed cases for both sexes (see figure – source: Public Health England). The data are separated according to whether the test was carried out in a hospital (pillar 1) or in the community (pillar 2). You can read more about the testing programme pillars on this Government website.
The Office for National Statistics publishes weekly provisional 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 early March. The latest ONS data for England and Wales published on 7 July with data up to week ending 26 June 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.
- 0 deaths in children aged 5–9 years old.
- 3 deaths in children aged 10–14 years old.
- 9 deaths in children aged 15–19 years old.
National Records Scotland reports mortality data slightly differently, using wider age bands. The latest data up to 5 July reports no COVID-19 related deaths for under 1-year-olds, or 1–14 year olds, with 28 deaths reported for the 15–44 year age band. Northern Ireland data up to 26 June reports no deaths in under 1-year-olds and 1–14 year olds, and 6 deaths in 15–44 year olds.
As of 5pm on 14 July the Government data dashboard reports the total number of deaths for all age groups in the UK at 44,968.
The ONS publishes regular results from a COVID-19 infection survey that seeks to estimate how many people in England have had COVID-19 infections. Testing of people in the community (excluding care homes and hospitals) has taken place since 26 April. Participants take their own nose and throat swab samples. ONS analysis shows that for the latest reporting period up to 5 July, an estimated 14,000 people in England had COVID-19 infection between 22 June and 5 July. This is equivalent to 0.03% of the population or 1 in 3,900 people. The estimated percentage of the community population who test positive has decreased since the survey began on 26 April (0.4%), but this downward trend is levelling off.
The data also show that there was no difference in the proportion of people who tested positive in any age group, but there was a wide range of uncertainty for the figure for each age group. It reported data on children by including them in the age range 2–19 years, rather than in several age cohorts from 0–18 years as other studies have done.
The survey will continue to collect data from up to 25,000 participants over the next 12 months across the UK. Self-swabbing of the nose and throat is difficult and could impair the sensitivity of the test, making it more likely that positive results are underestimated. The survey is also using antibody tests on blood samples collected from some participants aged over 16 years only. This will give a better estimate of overall COVID-19 prevalence because an antibody test gives information about whether an individual has been infected since the beginning of the pandemic, rather than whether someone is infected with live virus at a single point in time. This antibody test data show that around 6.3% of 3,298 people tested positive for SARS-CoV-2 antibodies. This analysis is weighted so that the sample is representative of the whole population. You can read more about serosurveillance in POST’s articles on immunity and antibody testing.
UK Research and Innovation (UKRI) has allocated £24.6m for COVID-19 research. Professor Matthew Snape (University of Oxford) was awarded funding to research COVID-19 immunity in children. The study is testing for the presence of SARS-CoV-2 antibodies in a sample of 3,500 children and young people aged 0–24 years across sites in England. The results will improve understanding about how many children and young people have been infected and what proportion of them had symptoms. The results will be published in PHE’s weekly COVID-19 reports; the first wave of data is expected week commencing 13 July. The data will also include a range of demographic characteristics, including ethnicity. There are very limited data on whether children from a black, Asian or minority ethnic background are at increased risk from COVID-19 (discussed later). Public Health England is also looking at SARS-CoV-2 antibodies in children by using samples collected for other disease surveillance projects.
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 in every 10,000 cases.
Reports about serious complications associated with COVID-19 infections in small numbers of children have raised concern. This research improves our understanding of how the disease manifests in children, informs how children are cared for and highlights where research studies should focus.
In early April, reports emerged of critically ill children (some of whom were COVID-19 positive) who had symptoms characteristic of a rare toxic shock syndrome that can arise from bacterial infections and symptoms of another condition called atypical Kawasaki disease. The WHO has published a scientific brief on this topic and, as with its other work to drive a harmonised international approach to COVID-19 research and clinical guidance, is coordinating clinical data collection to inform medical practice. The UK’s Paediatric Intensive Care Society states that serious illness as a result of COVID-19 is a very rare event in children. It has developed clinical guidance for health professionals, and primary care doctors have been alerted to how this condition presents in children. A study published in June reported on 58 hospitalised children who tested positive for COVID-19. These children all had an inflammatory syndrome that was associated with having the virus. A study published in July reported inflammation of the nervous system in four children with COVID-19. This is consistent with an emerging pattern of neurological problems in some adults with the infection.
Children at risk
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 cardio-vascular 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 underlying 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 black, Asian and minority ethnic groups may be at increased risk of having severe COVID-19 disease. This is consistent with the evidence of increased risk for adults from minority ethnic backgrounds 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.
- One study of eight children hospitalised with an inflammatory syndrome that was suspected to be linked to COVID-19 reported that six were of Afro-Caribbean descent. All the children subsequently tested positive for SARS-CoV-2 antibodies.
- In another study of 58 children hospitalised with COVID-19, 12 were white and 46 were from a black, Asian or minority ethnic background.
- One research study reported on the association between comorbidities (other health conditions) and severe disease in children admitted to a London hospital. Of five children with comorbidities, four were from a black, Asian or minority ethnic group. Of seven children without comorbidities admitted with COVID-19, five were from a black, Asian or minority ethnic group. The authors conclude that ethnicity might be an independent risk factor for severe disease in children.
These case studies involve very small numbers of children. Much larger samples 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 can be taken to limit the opportunities for transmission to take place between children and adults – notably closing childcare and educational settings. Research can also inform whether and how measures can be reversed or modified. Information about transmission is also critical in designing population immunisation programmes; although a COVID-19 vaccine is not expected for at least 12 months at the earliest if a successful vaccine candidate(s) is found. For example, children in the UK are immunised against seasonal influenza, which in addition to protecting the children themselves, also confers protection to the wider population because children readily transmit influenza virus in the community.
The extent to which children transmit the virus is not yet fully understood and is complicated by the fact that there are asymptomatic cases. Data from research in community clusters and larger studies that test population samples, such as those carried out in South Korea and Iceland, report fewer cases in children than adults, suggesting that children may be less likely to get the disease.
Transmission within families
Studies of early clusters of disease in families and in small groups showed that children were not the source of infection in those groups. For example, in a study of a disease cluster in the French Alps, a 9-year-old child with symptoms had made a large number of contacts during a trip to the Alps and then at three different schools. Of the 169 tested contacts, only one person tested positive.
Asymptomatic and pre-symptomatic transmission of the virus have been reported and there is also some evidence that those who have symptoms are more likely to transmit the virus than those who are asymptomatic. A study in the Netherlands reported that children have a minor role in transmission and that the virus is primarily spread between people of similar age. They also found that it is less common for adults to infect children, but when this does happen it tends to be within a household.
The Scientific Advisory Group for Emergencies (SAGE) is advising the UK Government on COVID-19. It has previously considered the possible risk to older people from contact with grandchildren in their families. One factor in the discussion about the consequence of school closures was of possible increased contact with grandparents. This is relevant because the risk from COVID-19 increase with age. As part of its analysis it has reviewed demographic data on parents and grandparents in the population. Parents with primary age children are generally younger than the general population (<50 years old). Within this group, adults with pre-existing health conditions (co-morbidities) are at increased risk from COVID-19 than those with no health conditions. A substantial proportion of people in high-risk age groups have one or more primary age grandchildren.
Transmission in schools
An Australian study looked at all COVID-19 cases reported in primary and high schools in New South Wales between March and mid-April and reported preliminary findings with data up to 21 April. 18 individuals (9 pupils and 9 staff) were identified as COVID-19 cases in 15 schools (10 high schools and 5 primaries). Close contacts of these cases included 735 pupils and 128 staff. There were no cases in any staff members as a result from contact with the infected school pupils. Two children were identified as having had COVID-19 and it is highly likely, but not certain, that they contracted the virus from the infected school contacts. A limitation of this study is that not all participants were tested for the virus.
Details from a study (not peer-reviewed) in the Netherlands reported to the Dutch Parliament was published by SAGE in April. The key findings were that there were no clusters of infection linked to schools or childcare settings and that children were least likely to infect other people.
Another study analysed transmission in schools in Ireland before school closures on 12 March. Six notified cases reported to the Public Health Department were the basis for an epidemiological contact tracing study of 1,155 people. The cases:
- Three adults – one teacher, two adults delivering short duration (<2 hours) on site educational session; all three had symptoms.
- Three children (one primary, two secondary) were identified. One child was asymptomatic.
Analysis showed that no infection was acquired in a school setting. Four cases were related to travel, one was linked to a close contact in a recreational setting outside school and the other in a work environment outside school. There was no onward transmission to children or adults in the schools and other settings. The children and adults mixed during high risk transmission activities including music lessons and choir practice.
A review of all the relevant research so far on transmission by children was published as a pre-print (this means that it has not yet been reviewed by other scientists) by a group of researchers led by University College London. From analysing research studies that undertook contact tracing, the authors conclude, based on the evidence so far, that children are 56% less likely to become infected than adults. This is in line with an earlier modelling study, which concluded that under 20-year-olds were approximately 50% less susceptible to infection than older age groups. On analysis of wider population level studies, the authors conclude that while it is possible that children may play a limited role in transmission, the evidence for this to date is weak. The reviewers highlight that many studies that seek to answer this question have limitations in terms of study design or quality, which make it difficult to draw conclusions with certainty.
The research so far is indicative that children may not play a significant role in spreading COVID-19, in contrast with other respiratory viruses such as influenza. More evidence from high quality large scale serosurveillance studies (that look at SARS-CoV-2 antibodies in a population) are needed to quantify the risk of transmission of the virus from children and how this differs from adults. Many such studies are underway.
Transmission of the virus in pregnancy and COVID-19 in newborns
There is some research on whether pregnant women are at greater risk from COVID-19 and if they pass the virus to their babies during pregnancy, birth and breastfeeding.
Research shows that pregnant women have the same COVID-19 risk factors as the general population, notably age, existing health problems including diabetes, asthma, high blood pressure, being overweight or obese. Being in a black or minority ethnic group is also a confounding risk for pregnant women. There is no evidence of an increased risk of miscarriage.
The UK has a real-time surveillance program of pregnant women who test positive for COVID-19. This allows them to be tracked throughout pregnancy and birth. The largest study on outcomes for pregnant women and their babies was reported in a UK study by the University of Oxford (not yet peer reviewed) using data from the surveillance program. The researchers analysed data from 427 pregnant women hospitalised with COVID-19. As with other research, most women were hospitalised in the later stages of pregnancy. One in 20 infants (12 infants in total) tested positive for COVID-19, of which half had a positive test immediately after birth. There have been other reports of infants testing positive for IgM antibodies to the virus in umbilical blood shortly after birth (IgM antibodies are made by the body first in response to an infection and do not cross the placenta). No virus was detected in these babies in subsequent testing and they did not have any symptoms. It is not yet possible to rule out whether the virus is passed to infants during pregnancy. Several studies have shown that maternal IgG antibodies against COVID-19 cross the placenta.
There is no evidence from the Oxford study, or other studies, to indicate that babies who test positive for COVID-19 are at increased risk of severe disease.
A study examined the breastmilk from two mothers with COVID-19. Their milk was tested for evidence of the genetic material from SARS-CoV-2 daily. The milk from one mother tested positive for 4 consecutive days. This coincided with mild COVID-19 symptoms in her infant, who also tested positive for the virus. However, it was not possible to conclude that the infant was infected through breastfeeding.
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
You can find more content from POST on COVID-19 here.
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