A new large-scale study finds the protection against COVID-19 infection offered by the Pfizer-BioNTech vaccine drops from 88% in the first month to 47% after five months. The Los Angeles Times reports on what it describes as "one of the largest and longest [studies] to track the effectiveness of a vaccine in Americans," which analyzed the medical records of almost 3.5 million people aged 12 and older enrolled in Kaiser Permanente Southern California's healthcare system, including over 1 million who received two doses of Pfizer's Comirnaty vaccine.
The peer-reviewed, Pfizer-funded study published Monday in the Lancet does offer good news, as the vaccine was still 90% effective at preventing hospitalizations across all age groups after six months, even as the percentage of COVID-19 cases attributed to the delta variant increased from 0.6% to 87%, per CNBC. Researchers concluded the waning protection was not the result of delta, but rather the passage of time: A fresh immunization was as effective at preventing an infection with delta as with any other version of the virus and breakthrough infections were found to be more closely linked to the passage of time than to a particular variant.
Study author Sara Tartof, an infectious disease epidemiologist at Kaiser Permanente, says a third dose of Comirnaty will likely extend protection against all strains—suggesting a third dose specifically designed to target delta might not be required—though for how long is unclear. She adds researchers continue to monitor the study group and will sound the alarm if hospitalization rates increase. Another recent study that has not yet been peer-reviewed found about half of 56 young and middle-aged adults "had no detectable neutralizing antibodies against the SARS-CoV-2 virus" six months after they were vaccinated with Comirnaty, the Times notes. (Read more coronavirus vaccine stories.)