COVID vax fortifies defences against emerging omicron variants in previously infected youths

For children and adolescents who have been previously exposed to SARS-CoV-2 infection, vaccination with BNT162b2 appears to provide additional protection against omicron BA.4 or BA.5 and XBB variant infections, according to a study from Singapore.

Specifically, vaccine effectiveness against subsequent infection with BA.4 or BA.5 was 74.0 percent (95 percent confidence interval [CI], 67.7–79.1) in fully vaccinated children (two doses) and 85.7 percent (95 percent CI, 80.2–89.6) in fully vaccinated adolescents (three doses). [Lancet Child Adolesc Health 2023;doi:10.1016/S2352-4642(23)00101-3]

Against subsequent infection with XBB, the protection obtained with full vaccination was lower at 62.8 percent (95 percent CI, 42.3–76.0) in children and at 47.9 percent (95 percent CI, 20.2–66.1) in adolescents.

Of note, receipt of full vaccination before the first SARS-CoV-2 exposure provided the greatest protection against BA.4 or BA.5 infection in children (85.3 percent, 95 percent CI, 80.2–89.1) but not in adolescents.

Other notable findings

“For unvaccinated children and adolescents who recovered from a past SARS-CoV-2 infection, there were clear additional benefits of getting at least one dose of vaccination in terms of protection against omicron BA.4 or BA.5 infections,” according to the investigators.

“[Meanwhile], children who received one dose before getting their first infection might not need to complete their second dose vaccination upon recovery as there was no incremental protection against subsequent omicron BA.4 or BA.5 infection (vaccine effectiveness 72.9 percent vs 73.6 percent). By contrast, a substantial improvement in protection was observed in adolescents with receipt of two doses (vaccine effectiveness rose from 55.8 percent to 70.4 percent),” they pointed out.

Finally, the variant of the past SARS-CoV-2 infection influenced vaccine effectiveness against subsequent infection with omicron BA.4 or BA.5. Specifically, previous infection with BA.2 conferred the highest protection (92.3 percent in children and 96.4 percent in adolescents), followed by BA.1 (81.9 percent in children and 95.0 percent in adolescents) and then delta, which conferred the lowest protection (51.9 percent in children and 77.5 percent in adolescents).

Continuous protection

“Our analysis … confirmed that vaccination continues to provide protection against omicron BA.4 or BA.5 and XBB variants in previously infected children and adolescents,” according to the investigators.

Given the reduced hybrid immunity of adolescents against the XBB variant than against the BA.4 or BA.5 variants, the investigators highlighted the potential of bivalent boosters to improve protection against XBB for adolescents.

Overall, the study makes a case for pre-emptive vaccination in children and adolescents not only to boost their immunity but also to potentially strengthen population resilience against future SARS-CoV-2 variants, the investigators said.

Insights into vaccine effectiveness against omicron BA.4 or BA.5 by sequence of vaccination dose and SARS-CoV-2 infection may “guide public health vaccination policy and development of optimum vaccination schedules for the paediatric population,” they added.

For the study, the investigators used national databases of all confirmed SARS-CoV-2 infections, vaccines administered, and demographic records maintained by the Ministry of Health of Singapore. A total of 135,197 youths aged 5–17 years (79,332 children and 55,865 adolescents) were included in the analysis of vaccine effectiveness against omicron BA.4 or BA.5, and 164,704 youths aged 5-17 years (97,235 children and 67,469 adolescents) in the analysis of vaccine effectiveness against omicron XBB.