BNT162b2 vax prevents delta, omicron infection in adolescents; benefits upped with booster dose

Full vaccination with the SARS-CoV-2 BNT162b2 vaccine reduced infection and hospitalization due to the delta and omicron variants of the SARS-CoV-2 infection, with an added benefit against the omicron variant in individuals who received a booster dose, according to a national study of Singaporean adolescents.

Using national databases, the researchers included 249,763 adolescents aged 12–17 years (median age 15 years, 49 percent female) in Singapore who received the BNT162b2 vaccine between September 1 and December 15, 2021 (delta variant wave) and between January 21 and April 28, 2022 (omicron variant wave). All individuals who presented to healthcare facilities with symptoms of SARS-CoV-2 infection during the same time periods were tested and individuals with confirmed infections (by PCR or antigen rapid testing), among those without prior SARS-CoV-2 infection, were included.

The total cohort contributed >56.2 million person-days of observation. Of the group, 76.1 percent were fully vaccinated (defined as 8 days following receipt of the second vaccine dose), 16.7 percent had received a booster dose, and 5.2 percent were unvaccinated. Of the 49,921 individuals who developed COVID-19, 0.7 percent were admitted to hospital.

Compared with unvaccinated individuals, individuals who were fully vaccinated documented 66 and 25 percent vaccine effectiveness against infection with the delta and omicron variants of the SARS-CoV-2 virus, respectively*. [Lancet Infect Dis 2022;doi:10.1016/S1473-3099(22)00573-4]

Vaccine effectiveness against hospitalization due to infections with the delta or omicron variants was 83 and 75 percent, respectively, in those who were fully vaccinated vs unvaccinated.  

Vaccine effectiveness against infection and hospitalization due to the omicron variant was further increased in individuals who received a booster dose of the vaccine (8 days after receiving a third dose) compared with unvaccinated individuals (56 and 94 percent, respectively).

Vaccine effectiveness against infection in fully vaccinated individuals waned over time, both for the delta variant (from 75 percent following completion of the second dose to 57 percent at 150–179 days) and omicron variant (from 47 percent to 16 percent). Booster doses first increased the effectiveness of the vaccine against infection from omicron (60 percent 14–29 days after the third dose), before waning (40 percent after 60 days).

In contrast, vaccine effectiveness against hospitalization among fully vaccinated individuals remained stable over time, for hospitalization related to the delta variant (76–89 percent from 8–149 days after the second vaccine dose) and omicron variant (59–89 percent from 8–239 days after the second vaccine dose), and increasing following booster vaccination (84–96 percent against omicron-related hospitalization up to 60 days post-third dose).

There were no incidents of reinfection during the study period.

“Our findings add to the existing body of evidence showing that primary series vaccine effectiveness against SARS-CoV-2 infection was lower for omicron than for delta, and gradually waned over time for both variants,” said the authors.

Booster benefits highlighted

“[W]e showed that a booster dose provided the greatest protection against both infection and hospitalization,” said the authors. “Specifically for omicron, the booster increased protection against hospitalization to levels similar to those against delta after the primary series.”

“These findings highlight the usefulness of the booster dose in reducing stress on healthcare systems and maintaining individual protection against severe disease in an omicron-dominated wave,” they concluded, calling for further research into identifying the long-term waning of booster dose effectiveness.

They acknowledged that lack of information on certain comorbidities may have affected the findings. Additionally, hospitalization, being a clinical decision, is a “subjective measure of disease severity.” A lack of routine genomic testing also meant that variant type was subject to assumption based on the local infection wave.

*following adjustment for age, gender, ethnicity, socioeconomic status, and daily infection rate