COVID-19 mRNA Vaccines Cut Emergency Visits and Hospital Stays by 40% in Children Under 5

Two or more doses of a COVID-19 mRNA vaccine were 40% effective at keeping children aged 6 months–4 years out of the emergency department and hospital, according to a CDC study of the first year the vaccines were available to this age group. Yet 86% of the children studied had not had a single dose.

Why it was studied

COVID-19 in young children is often mild or has no symptoms, but some children, including those with certain chronic conditions, can become seriously ill. The mRNA vaccines were recommended for children aged 5 and over in November 2021 and for those aged 6 months–4 years in June 2022, with bivalent vaccines authorised during December 2022–April 2023. Coverage in young children has stayed far below that in adults: about 5% nationwide had completed the primary series since January 2023. So there was little evidence on how well the vaccines protect them.

How it was done

The New Vaccine Surveillance Network watches for acute respiratory illness in children at seven pediatric medical centres, in Cincinnati, Houston, Kansas City, Nashville, Pittsburgh, Rochester (New York) and Seattle. From July 1, 2022, to September 30, 2023, it enrolled children aged 6 months–4 years treated in an emergency department (ED) or hospital for respiratory illness. Parents were interviewed, charts reviewed, and every child tested for SARS-CoV-2 and seven other respiratory viruses. Vaccination was checked against state immunisation registries.

The design was test-negative: children who tested positive were compared with those who tested negative, by how many doses each had received, adjusting for race, age, week of enrolment and site.

What they found

Children aged 6 months–4 years enrolled each week, by SARS-CoV-2 test result, with the share vaccinated. CDC, New Vaccine Surveillance Network.

• Few had COVID-19. Of 7,434 children, 387 (5.0%) tested positive and 7,047 (95.0%) negative. Weekly positives peaked in late August to early September of both 2022 and 2023.
• Most were unvaccinated: 86% had no dose, 4% one dose and 10% two or more.
• Children with COVID-19 were younger (median 15 months against 22) but otherwise alike: the same median two-day stay, and no difference in sex, race and ethnicity, insurance, prematurity or underlying conditions. They were less likely to need oxygen or high-flow nasal support. Two were intubated, none needed ECMO and none died.
• Other viruses often came too. Another virus was found in 140 (36.2%) of the children with COVID-19, half of them rhinoviruses or enteroviruses and 21.4% respiratory syncytial virus.

Protection

These match other estimates for this age group, which range from 29% for two Moderna doses to 43% for three Pfizer-BioNTech doses.

Who was vaccinated

Coverage with two or more doses ranged from 3.9% to 27.9% across sites, highest in Seattle, about two to six times the other sites, in line with the region's high coverage for other childhood vaccines. It was 25.3% among privately insured children, 19.0% among White children and 2.5% among Black children. Compared with White children, Black children were about seven times and Hispanic or Latino children about three times less likely to have had two or more doses, which the authors say shows the continued need to widen access and address vaccine hesitancy. Vaccinated children were older (median 27 months against 21).

Limitations

• More and more children have antibodies from earlier infection, which may affect both the estimates and how severe illness appears.
• With so few vaccinated, vaccinated children may differ from the rest; for example, those with underlying conditions may be both likelier to be vaccinated and likelier to be hospitalized.
• Enrolment may be biased in ways that vary by site, such as enrolment days per week and interpreters for families who do not speak English.
• Low coverage and few cases made the estimates imprecise, and ruled out analysis by time since vaccination, setting or vaccine.
• Moderna's primary series is two doses and Pfizer-BioNTech's three, so "two or more doses" may understate the protection of a completed Pfizer-BioNTech series.

What it means

Few children in this age group with respiratory illness needed emergency or hospital care for COVID-19, even with low coverage and several Omicron subvariants circulating, suggesting most have mild illness or some immunity from earlier infection. The findings support vaccinating every child from 6 months of age, stress completing the primary series, and may help clinicians counsel parents. The authors add that testing for many viruses at once, a strength of the network, shows co-infections that future effectiveness estimates may need to account for.

Sources

• Tannis A, Englund JA, Perez A, et al. "SARS-CoV-2 Epidemiology and COVID-19 mRNA Vaccine Effectiveness Among Infants and Children Aged 6 Months–4 Years — New Vaccine Surveillance Network, United States, July 2022–September 2023." MMWR 2023;72(48). https://www.cdc.gov/mmwr/volumes/72/wr/mm7248a2.htm