These findings mirror the trend in the general population: Omicron seems less likely than Delta to cause hospitalization or death, especially in immunized and younger populations. But scientists are still trying to work out why Omicron has led to disproportionately more hospitalizations in children. In the United States, for example, children make up about 5% of all COVID-19 hospitalizations — a proportion up to four times higher than that of previous coronavirus waves.
One potential explanation is that the variant’s extremely high transmissibility, when coupled with a lack of built-up immunity from vaccination or past infection, leaves children more vulnerable to Omicron, compared with adults who have had access to vaccines for months. Most countries have not yet authorized a COVID-19 vaccine for children under the age of 5, and some have not yet offered it to children under 12. Even in the United States, which has authorized COVID-19 vaccinations for 5–11-year-olds, less than one-third of children in that age group have received a jab.