Study yields important findings on COVID-19 vaccination and previous SARS-CoV-2 infection in children under 12 years of age

A recent study published in Lancet infectious diseases examined the effects of prior coronavirus disease 2019 (COVID-19) infection and vaccination on subsequent infection with the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in children.

SARS-CoV-2 Omicron is a highly transmissible variant that can cause severe illness. Previous SARS-CoV-2 infection and vaccination with COVID-19 have been reported to alleviate the risks of Omicron infection and severe COVID-19 outcomes in adolescents and adults. However, data on the effectiveness of the vaccine in children under 12 years of age are sparse, while the effects of prior infection on reinfection with SARS-CoV-2 Omicron remain poorly understood.

About the study

In the present study, investigators characterized the effects of SARS-CoV-2 vaccination and prior COVID-19 on reinfection with Omicron in children younger than 12 years of age in North Carolina. Two age groups of children were defined, 0-4 and 5-11. The team used data from a surveillance system that includes positive test results for all COVID-19 cases and reinfections.

Vaccination data was obtained from the COVID-19 Vaccination Management System through January 6, 2023. Hospitalization and death data were collected between March 11, 2020, and January 6, 2023. Healthy children and those with underlying conditions. Population-level prevalence data for SARS-CoV-2 variants was accessed.

The investigators considered two outcomes: COVID-19 and a composite endpoint of hospitalization or death. The team looked at the effects of primary vaccination and previous infection on the outcomes. They examined the efficacy of the booster regimen relative to primary vaccination and compared the efficacies of monovalent and bivalent boosters.

recommendations

As of January 6, 2023, more than 39,000 children ages 5 to 11 years received the partial vaccine, 216,330 received the full vaccine, and 46,895 received a booster. In addition, 11,235 children under five years of age were partially vaccinated, 28,066 were fully vaccinated, and 11,529 received a booster. There were about 116,108 and 42,484 infections among vaccinated and unvaccinated children aged 5 to 11 years, respectively.

Among unvaccinated COVID-19 cases aged 5 to 11 years, there were 141 hospitalizations and five deaths, while among vaccinated COVID-19 cases there were 52 hospitalizations and one death. Among unvaccinated children under five years of age, 27,449 infections were documented, including 161 hospitalizations and one death, while among those vaccinated there were 2,094 infections, six hospitalizations, and zero deaths.

The effectiveness of the primary vaccination series against infection was 59.9% one month after the first dose, 33.7% after four months, and 14.9% after 10 months in children aged 5 to 11 years, with lower estimates for Hispanic and black children than for children of other ethnic groups. The appearance of new Omicron variants (BQ and XBB (sub)lineages) decreased the efficacy of the vaccine.

Among previously infected children aged 5 to 11 years, the effectiveness of the primary series against infection was 65.3%, 26.4%, and 10.6% at 1, 3, and 6 months after the first vaccination, respectively. Among children without prior infection, these estimates were 59.7%, 36.8%, and 28.6% at one, three, and six months after the first dose, respectively.

The effectiveness of the primary series against serious outcomes was 73.3% one month after the first dose and decreased after that. The efficacy of a previous infection with Omicron against reinfection with Omicron was 79.9% after three months and 53.9% after six months. The long-term efficacy of previous infection was superior in vaccinated children.

The efficacy of a prior Delta variant infection against reinfection was similar between vaccinated and unvaccinated children. Prior infection was 83.8%, 76.2%, and 64.9% effective against severe outcomes after three, six, and nine months, respectively. The efficacy of a monovalent booster against infection was 23.1% at two months; in contrast, a bivalent booster was 47.3% effective after two months.

In children under five years of age, the efficacy of the primary series was 63.8% at two months after the first vaccination and 58.1% at five months. The efficacy of a previous infection with Omicron against reinfection with Omicron was 77.3% after three months, 64.7% after six months and 45.2% after nine months. Additionally, the efficacy of a prior infection against severe outcomes was 61.4%, 58.4%, and 55.1% after three, six, and nine months, respectively.

conclusions

In summary, vaccination with the mRNA-1273 or BNT162b2 vaccine in children was effective against SARS-CoV-2 infection and had serious outcomes, but efficacy decreased over time. The efficacy of bivalent boosters was greater than that of monovalent boosters. Prior infection conferred strong immunity against reinfection(s), but protection waned over time. Additionally, vaccination provided additional immunity among those with primary infection; a previous infection with Omicron elicited robust immunity, regardless of vaccination status.