(CNN) The Pfizer/BioNTech vaccine is 93% effective in preventing hospitalization due to Covid-19 among children ages 12 to 18, according to a study by the US Centers for Disease Control and Prevention. Vaccine effectiveness differed only slightly within that age group, with 91% effectiveness for children age 12 to 15 and 94% effectiveness for those age 16 to 18.
The study included 464 patients -- 179 hospitalized with Covid-19 and 285 hospitalized for other reasons -- across 19 pediatric hospitals in 16 states between June and September 2021, a time period when the Delta variant was dominant. The majority of patients had at least one underlying condition (72%) and attended in-person school (68%), and most patients were from southern states, as Covid-19 transmission was high in that region during this timeframe.
Patients were considered fully vaccinated against Covid-19 if they had received their second dose of the Pfizer/BioNTech vaccine at least 14 days before illness onset. Those partially vaccinated -- with only one dose or with less than 14 days since the second dose -- were excluded from the analysis.
Among the 179 patients hospitalized with Covid-19 in the study, 97% were unvaccinated. All of the critically ill patients were unvaccinated, including about 43% (77 patients) were admitted to an intensive care unit, 29 received life support during hospitalization and two died.
Since August 2020, more than 65,000 children have been hospitalized with Covid-19 and nearly 700 have died, according to CDC data.
Clinical trial data from Pfizer/BioNTech found the vaccine to be 100% effective against hospitalization among children age 12 to 15, and this real-world analysis also found vaccination to be highly effective in reducing the risk of hospitalization among those age 12 to 18.
Currently, 46% of children age 12 to 15 and 54% of those age 16 to 17 are fully vaccinated, according to CDC data, a smaller share than any adult age group.
"(These) findings reinforce the importance of vaccination to protect U.S. youths against severe COVID-19," according to the study authors. "These data suggest that increasing vaccination coverage among this group could reduce the incidence of severe COVID-19 in the United States. Further, as in-person school attendance increases, multicomponent preventive measures to reduce the incidence of severe COVID-19 among adolescents, including vaccination, are imperative."