The effectiveness of Pfizer and BioNTech’s Covid-19 vaccine in teens fades rapidly in the weeks after vaccination, according to research published Wednesday in JAMA Network Open, a finding that fits with research in adults as pharma firms rework their shots to target newer coronavirus variants like omicron.
The effectiveness of Pfizer’s Covid vaccine “waned over time” and offered only “limited protection” as early as 30 days after the second dose, according to a peer reviewed study of teens ages 12-18 in South Korea between late July 2021 and late January 2022.
Of the roughly 3.2 million teens involved in the study, nearly 29,300 tested positive for Covid after vaccination and 11 were seriously unwell and needed major hospital support like mechanical ventilation or kidney replacement therapy, the researchers said.
Unvaccinated teens made up a small fraction of the study group—more than 81% had received at least one shot, 75% had been double vaccinated and 9% had received a third dose—but represented more than half (55%) of teens with an infection, including all 11 with critical illness.
The researchers said the findings are in line with other research showing that protection against infection drops off rapidly after vaccination but remains strong against serious illness.
The finding of sustained protection against critical illness suggests that two doses of Pfizer’s shot might be enough to protect teens against severe disease, albeit with waning immunity, the researchers added.
The researchers note that the study’s findings may have been influenced by potential changes in testing behavior based on vaccination status during the omicron surge, different virus variants spreading during the study and differences in when people were vaccinated.
The findings are not surprising and are in line with substantial evidence that protection against infection is transient after immunization. Initial Covid vaccine trials were not able to assess how durable the protection a vaccine provided was beyond a few months or against the evasive new variants that dominate today. However, time has revealed that the vaccines offer high levels of protection against serious illness, hospitalization and death and that this is sustained over a much longer period of time. This, not protection against infection, is considered by experts to be the most important function of vaccination. Boosters are also capable of topping up this protection when it does flag, though experts are divided over whether they are needed for everyone or whether additional boosters are beneficial for at-risk groups.
What To Watch For
New vaccines. The vaccines in widespread use are based on the original coronavirus strain discovered in 2020, a virus that differs significantly from the variants spreading today. Major vaccine makers like Pfizer and Moderna are developing another generation of vaccines to target newer variants for future booster campaigns. Some in the works target both the original strain and a newer variant—the two-pronged approach is known as a bivalent vaccine—and the U.K. became the first country to approve Moderna’s omicron/original booster vaccine.