Knowledge base (as of February 2022)

The omicron variant has a much higher transmission rate than previous variants. At the same time, omicron has lower virulence, and a smaller proportion of infected people will need admission to hospital and intensive care units. The decisive factor is the balance between higher transmissibility and lower virulence, i.e. the overall burden of disease. It is expected that the latest wave with the omicron variant will cause significantly increasing infection also among children and adolescents.

Disease burden among children and adolescents

• The individual risk of a severe disease course among children and adolescents is very low. The omicron variant is less virulent and more often leads to upper respiratory tract symptoms than earlier variants.
• To date (as of 2 February 2022), there have been 276,938 children and adolescents aged 0-17 diagnosed with COVID-19. Among these, 125,615 are in the age group 5-11 and 89,253 in the age group 12-15. This means that about 33% of children ages 5-11 and 35% of adolescents aged 12-15 have been diagnosed with COVID-19. There are probably significant numbers of undetected cases, and earlier in the pandemic it is estimated that approximately 60% of cases of infection were detected. The share of undetected cases is probably even higher today. 89% (n=111,417) of transmission among ages 5-11 and 91% (n=80,958) of transmissions among ages 12-15 has happened in the period from week 33/2021 till start of week 5/2022. At the same time there has only been under 200 hospital admissions among children and adolescents aged 0-17 throughout the whole pandemic. That means that at least 99.9% of the infected have not been admitted to hospital because of COVID-19, and the share of infected people admitted has dropped. The median admission time for acute COVID-19 is 1 day.
• Although there were many children and adolescents infected in autumn 2021, this did not led to an increase in hospital admissions of children. The proportion who develop multi-inflammatory syndrome (MIS-C) has also decreased, without us knowing why.
• In comparison, in the autumn of 2021 (week 30-51) there were 2507 admissions for RS virus aged 0-4 years and 76 aged 5-17 years (compared to 1000-2000 admissions in a normal season). In a normal influenza season, there are normally approximately 500 admissions aged 0-17 years.
• Preliminary information indicates that the omicron variant leads to hospital admission for children less often compared to the delta variant. There is still limited knowledge about omicron in children, and currently there is only one published study on this but, combined with surveillance data and credible media reports from different countries, this indicates that omicron does not cause a more severe disease course among children than other variants.
• According to the latest technical briefing published by the UK (31.12.21), there is a lower risk of hospital admission among children aged 5-17 years with omicron compared to delta (Risk 42% compared to the delta variant, HR 0.42, 95% CI 0.28-0.63).
• A study (preprint) from the USA compared outcomes among SARS-CoV-2 infected people during a period where the delta variant was dominant and a period when the omicron variant was about to take over (15-24 December). The results show fewer outpatient consultations and admissions for children and adolescents in all age groups (0-17 years) infected in the “omicron period” compared with the “delta period”. The researchers did not investigate which variant the patients in the two groups were infected with. In the "omicron period", in reality, only between a quarter and a half of patients in the United States were infected with the omicron variant. This indicates that the risk reductions may be even greater than reported. Another study from the same group of scientists (preprint) concluded that children under 5 years old, who were infected for the first time while the Omicron variant dominated (prevalence > 92%), had significantly reduced risk of serious illness compared with children infected for the first time when the Delta variant dominated.
• It is difficult to assess the information from countries that report admissions among children where they do not differentiate between admissions due to COVID-19 or where the coronavirus is detected randomly, e.g. by screening inpatients. In addition, the health of children in other countries and access to health services are not directly comparable with Norway.

Transmission in schools

There is transmission in schools and childcare centres and it has previously been shown that the probability of further spread is low for each individual case. The main pattern is that infection is diffusely spread in the child population, with small clusters of infection rather than large outbreaks.

• Data from NIPH's registers (Beredt-C19) up to and including the autumn semester 2021 show that the majority of COVID-19 cases in childcare centres and primary schools are included in infection clusters in 1-2 cases and that infection clusters with more than 10 cases are rare. In lower secondary schools, the majority have also belonged to infection clusters of 1-2 cases in most weeks, but in weeks with a higher incidence of infection, the majority are included in infection clusters of 3 or more, and it has been more common with infection clusters of 10-20 people or more in lower secondary schools (Wuhan, alpha and delta variant).
• The Corona Child Study (for the Wuhan and alpha variants) showed that when a child was an index case, 1.4% of close contacts in schools and childcare centres were infected.
• A study (preprint) based on NIPH's registers (Beredt-C19) identified children or employees who tested positive and calculated the number of secondary cases among children and employees at the same school within 14 days. Secondary infection, from child to child, and from child to employee, was only found in 0.3% of cases. The analyses were made during the Wuhan and alpha periods, but were updated for the delta variant this autumn. These data are not yet published, but show that secondary infection increased 1% between children, while it remained at 0.3% from children to employees. We do not yet have similar data for the omicron variant.
• The risk of transmission has previously been shown to be significantly higher in households. This has been shown both in registry studies (the Wuhan variant) and in the contact tracing study Corona-house (the Wuhan and alpha variant). Secondary infection occurred in 50% of households, with 78% for the alpha variant and 43% for variants that are not of concern (non VOC).
• During the ongoing omicron wave, with high transmission rates in society, the monitoring of cases in schools will have lesser value. When there are this many transmission introductions happening, it is impossible to estimate the share of transmission happening in schools.

Links

• Facts about the virus and COVID-19 disease
• Weekly reports
• Updates from ECDC July 2021