Department of Research & Evaluation News

Adolescents who received 3 doses of the Pfizer–BioNTech COVID vaccine were better protected against infection with SARS-CoV-2 — the virus that causes COVID-19 — than adolescents who received only 2 doses, according to a study of more than 3,000 Kaiser Permanente Southern California members ages 12 to 17 and published on August 3, 2022, in JAMA Network Open.

“Our findings really underscore the importance of boosters for people in this age group,” said the study’s lead author Sara Y. Tartof, PhD, an epidemiologist with the Kaiser Permanente Southern California Department of Research & Evaluation and a member of the faculty of the Kaiser Permanente Bernard J. Tyson School of Medicine, both in Pasadena.

In the United States, people ages 12 to 17 are recommended to receive 2 doses of the Pfizer vaccine, followed by a third dose at least 5 months later. However, most studies of the vaccine have focused on adults, and of studies involving adolescents, few have explored how the effectiveness of 2 doses wanes over time. Even fewer have investigated the effectiveness of a third dose.

“There was a dearth of data for these younger patients,” Dr. Tartof said, “So our study helps to fill a gap in our understanding of Pfizer vaccine protection in adolescents.”

Boosters confirmed effective

The researchers evaluated the electronic health records of 3,168 Kaiser Permanente members ages 12 to 17 who had visited an emergency department or an urgent care facility for respiratory symptoms between November 2021 and March 2022. All patients included in the analysis were tested for COVID-19, but only 978 tested positive, some with the delta variant and some with omicron. Some patients were unvaccinated and some had received 2 or 3 doses of the Pfizer vaccine.

Analysis of the patient data revealed that 2 doses of the vaccine were 89% effective against delta infection and 73% effective against omicron within the first 2 months after vaccination. However, by 6 months and later, effectiveness had waned to 49% for delta and 16% for omicron.

“The encouraging news, though, is that we found that a third dose bumped protection against omicron back up to 87%, which is excellent,” said co-author Bradley Ackerson, MD, a Kaiser Permanente South Bay Medical Center pediatric infectious disease specialist and an investigator with Kaiser Permanente Southern California Department of Research and Evaluation.

The researchers said the results highlight the importance of boosters for adolescents, and they suspect it is still beneficial even with a new omicron variant — dubbed BA.5 — currently dominating infections.

“We know that the original omicron variant was about as contagious as measles, which is extremely contagious, and BA.5 is even more contagious,” Dr. Ackerson said. “So, the likelihood of becoming infected is very high. However, even if a person becomes infected, being vaccinated always reduces the risk of severe outcomes — such as hospitalization and ending up on a ventilator.”

Future outlook for a “crafty” virus

Further research will be needed to evaluate the long-term effectiveness of a third Pfizer vaccine dose for adolescents, and how it may wane over time. Meanwhile, vaccine manufacturers are working on new vaccine formulations that are designed to better protect against infection with BA.5 and BA.4, another recent omicron variant.

“New formulations are coming, but we don’t know exactly when,” Dr. Tartof said. “Right now, we can take action by boosting adolescents with the existing vaccine.”

Dr. Ackerson added, “This is a very crafty virus, probably even craftier than seasonal flu, and it’s likely we will have to continue to update vaccines in the future, just as we do for the flu.”

The researchers also emphasize that future COVID-19 vaccine research should continue to focus on adolescents. “It is important to study this age group, not just for prevention of disease for adolescents themselves, but because they are heading back to school and other group activities and are likely to play a bigger role in spreading COVID-19 to vulnerable people than they were when they stayed home,” Dr. Ackerson said.

In addition to Dr. Tartof and Dr. Ackerson, other authors on the study were Timothy Frankland, MA, of the Kaiser Permanente Hawaii Center for Integrated Health Care Research; Jeff Slezak, MS, Vennis Hong, MPH, and Fagen Xie, PhD, of the Department of Kaiser Permanente Southern California Department of Research & Evaluation; and Laura Puzniak, PhD, Srinivas Valluri, PhD, Luis Jodar, PhD, and John McLaughlin, PhD, of Pfizer Inc.