COVID shots hold up against Omicron XBB for youngest kids in SG

The monovalent mRNA vaccine helped stave off severe COVID-19 outcomes in children aged 1 to 4 years during the Omicron wave, as shown in a study from Singapore.

Among children who had never been infected, completion of the primary vaccine series—particularly with mRNA-1273—yielded a vaccine effectiveness of 63.3 percent (95 percent confidence interval [CI], 40.6–77.3) against confirmed SARS-CoV-2 infection. Partial vaccination provided lower protection, with a vaccine effectiveness of 45.2 percent (95 percent CI, 24.7–60.2). [JAMA Pediatr  2023;doi:10.1001/jamapediatrics.2023.4505]

Meanwhile, among previously infected children, at least a single dose of mRNA-1273 had a vaccine effectiveness of 74.6 percent (95 percent CI, 38.7–89.5) against reinfections.

“These estimates were derived against a background of Omicron XBB circulation including sublineages (XBB 1.5/XBB 1.9/XBB 1.16),” from 1 October 2022 to 31 March 2023, according to the investigators.

“In terms of COVID-19 hospitalizations, the incidence rate was nil for fully vaccinated children compared with 10.0 and 1.6 per million person-days for unvaccinated/infection-naïve and previously infected children, respectively,” they added.

A total of 121,628 children in Singapore aged 1 through 4 years (median age 3.1 years, 50.9 percent boys, 65.5 percent Chinese) were included in the analysis. Of these, 45,693 (37.6 percent) had prior SARS-CoV-2 infection, most of whom contracted the infection during the earlier Omicron BA.1/2 wave.

Overall, the study population contributed 21,015,956 person-days of observation, of which 19,741,062 person-days (93.9 percent) were unvaccinated, 965,424 person-days (4.6 percent) were partially vaccinated, and 309,470 person-days (1.5 percent) were fully vaccinated. Most of the vaccinated children received the mRNA-1273 vaccine. Only a few children younger than 12 months had received vaccination, leading to this age group being excluded.

During the study period, SARS-CoV-2 infection occurred in 3,888 children, of whom 138 (3.5 percent) required hospitalization. Six children (0.2 percent) progressed to severe COVID-19 infection, and all of them were unvaccinated. None of the fully vaccinated children were hospitalized. There were no deaths documented, although two cases of multisystem inflammatory syndrome in children (MIS-C) were reported among unvaccinated children.

Is there a need to vaccinate children?

“Whether children younger than 5 years should be vaccinated against COVID-19 infection remains debatable, given that children are much less likely to have severe disease requiring hospitalization,” the investigators said. [BMJ 2022;378:o1892]

“Indeed, rates of hospitalization and severe COVID-19 infection in our cohort were extremely low. However, rapid increases in paediatric COVID-19 infections coinciding with periods of high community transmission may still place healthcare systems under strain,” they added.

The investigators warned that Omicron infection may not be mild, especially among previously uninfected and unvaccinated children, when compared with influenza or parainfluenza infection. For example, infection with Omicron BA.2 comes with a higher risk of paediatric intensive care unit admission, along with neurologic complications. Fatal fulminant cerebral oedema, although rare, has been reported among unvaccinated children. Additionally, the long-term effects of acute SARS-CoV-2 infection must be considered in the paediatric age group. [Emerg Microbes Infect 2022;11:1742-1750; J Pediatric Infect Dis Soc 2023;12:99-103; Lancet Child Adolesc Health 2022;6:614-623; J Infect 2022;84:158-170]

“The potential benefit of COVID-19 vaccination in minimizing acute and long-term sequelae of SARS-CoV-2 infection needs to be considered in tandem with safety data, with no serious adverse events associated with vaccination,” they said. [MMWR Morb Mortal Wkly Rep 2022;71:1115-1120]

In Singapore, eight adverse events after vaccination (0.05 percent of all doses administered) among children younger than 5 years were reported to the Health Sciences Authority as of 31 December 2022. This number is relatively low compared to the overall rate of adverse events after vaccination across all age groups of 0.11 percent. [https://www.hsa.gov.sg/docs/default-source/hprg-vcb/safety-update-on-covid19-vaccines/hsa-safety-update-no-14-on-covid-19-vaccines-(31-december-2022).pdf] 

Despite the available data on COVID-19 vaccine effectiveness and safety in children, vaccine hesitancy remains, with around 15.9 percent of Singaporean parents expressing reluctance to get their children vaccinated. This hesitancy, according to the investigators, is rooted in parental beliefs and perceptions. [Vaccines 2021;9:1415]

The investigators hope that the results of their study may help parents to weigh the benefits against the potential risks of vaccination in children younger than 5 years. “The potential benefit in minimizing acute and long-term sequelae of SARS-CoV-2 infection in this age group may outweigh the minimal adverse effects arising from vaccination.”