The uptake of COVID-19 booster doses is lower than that of the primary vaccine series in a nationwide cohort of children and adolescents in Singapore, influenced by parental vaccination and socioeconomic statuses, as shown in a study.
“Overall uptake of COVID-19 vaccine declined progressively across successive vaccination doses in both age groups,” the authors reported.
Among adolescents between 12 and 17 years of age, primary vaccine coverage was high at 95.8 percent. The percentage of adolescents who received the first booster dose remained high at 92.5 percent but sharply declined to 18.6 percent for the second booster dose. [Int J Infect Dis 2026;doi:10.1016/j.ijid.2026.108686]
The corresponding uptake among children between 5 and 11 years of age was 75.8 percent for the primary series, 46.1 percent for the first booster dose, and 20.2 percent for the second booster dose.
“The temporal trend for decline in vaccination uptake for successive booster doses was statistically significant in both children and adolescents,” the authors noted.
Determinants of vaccination
Parental COVID-19 vaccination status showed the strongest association with time to uptake of primary COVID-19 vaccine series and receipt of booster doses.
For the primary vaccine series, uptake was substantially delayed among children whose parents were both unvaccinated than those whose parents were both vaccinated (5–11-year cohort: adjusted hazard ratio [aHR], 0.28; 12–17-year cohort: aHR, 0.11). Results were similar for the first booster dose, with significantly slower uptake among children with neither parent vaccinated (5–11-year cohort: aHR, 0.87; 12–17-year cohort: aHR, 0.51). No significant associations were observed for second booster dose uptake.
Socioeconomic status, determined based on housing type, showed a U-shaped association with vaccination timing across doses. Children residing in lower-income public housing (1–2 room flats) and those living in higher-income private housing had slower uptake of the primary series and booster doses in both age cohorts.
“This U-shaped pattern highlights that barriers and facilitators to vaccination differ across socioeconomic status contexts. For example, lower-income families may have more limited access to accurate information on vaccination, whereas higher-income families may have different risk perceptions or preferences regarding paediatric vaccination,” the authors explained.
Other determinants of timeliness of vaccination included ethnicity and influenza vaccination history in both age cohorts. For instance, uptake of both the primary series and booster doses was slower among children of Indian or other minority ethnicities vs Chinese children. Meanwhile, recent influenza vaccination was associated with faster uptake of the primary series and booster doses.
“Overall, public health interventions should take a family-centred holistic approach, where preventive strategies should integrate the principles of shared decision-making, respect for cultural values and preferences, and recognition of the family’s central role in a child’s health,” the authors said.
Study details
The study included 265,971 children and 176,428 adolescents. The sex distribution was balanced. In terms of ethnicity, most children were Chinese (68–71 percent), between 17 percent and 18 percent were Malay, and 9 percent were Indian. Overall, most children resided in public housing, with the largest proportion living in 4- or 5-room public housing flats, while a smaller proportion resided in 1-2 room public housing or private housing.
“During the study period, Singapore had implemented vaccine-differentiated public health and social measures that were applied primarily to adolescents and adults, but not to younger children,” the authors noted.
“These policy differences likely contributed to a stronger extrinsic incentive for timely vaccination among adolescents compared with younger children, independent of parental attitudes or perceived medical risk, and may partially explain the faster uptake observed in the older age group during the Delta period,” they added.
The authors acknowledged several study limitations, including the possibility that some delays in vaccination could have been driven by clinical guidance rather than true hesitancy. For instance, patients recovering from an acute COVID-19 infection were initially advised to defer vaccination for 6 months (which is later revised to 3 months) after recovery.
“Second, the study did not delve into detailed parental sociodemographic information and psychosocial factors that might more precisely explain parental influence on vaccination decisions… Additionally, interpretation of second booster uptake should be contextualized by the absence of a formal national recommendation for children and adolescents during the study period. Some parents may have adopted a “wait-and-see” approach in the absence of policy guidance, potentially underestimating eventual uptake in our study period,” they said.