Those individuals who received older versions of vaccines did not see significantly reduced risks of severe COVID-19 outcomes.
Study investigators said that when comparing individuals who were unvaccinated, against those individuals who received only older versions of COVID-19 vaccines the latter group did not see statistically significant reduced risk of COVID-19 outcomes, including hospital admission.
In a new study published in JAMA Internal Medicine, the Pfizer-BioNtech BNT162b2 XBB COVID-19 vaccine showed a 62% protection against hospitalization.
“Adjusted estimation of effectiveness of the BNT162b2 XBB vaccine received a median of 34 days prior vs not having received an XBB vaccine of any kind was 62% (95% CI, 32%-79%) against COVID-19 hospitalization and 58% (95% CI, 48%-67%) for ED/UC visits,” the investigators reported. The investigators noted that when comparing individuals who were unvaccinated, against those individuals who received only older versions of COVID-19 vaccines, the latter group did not see a statistically significant reduced risk of COVID-19 outcomes, including hospital admission.
“Individuals who did not receive an XBB vaccine and had received only older versions of COVID-19 vaccines had little, if any, additional protection compared with unvaccinated individuals against COVID-19 end points, including hospital admission, regardless of the number or type of prior doses received,” the investigators wrote.
Study Parameters
The investigators included patients 18 years and older who were treated in the Kaiser Permanente Southern California health system from October 10, 2023, through December 10, 2023. Investigators wanted to estimate the effectiveness of the BNT162b2 XBB vaccine against COVID-19–associated hospitalization and emergency department (ED) or urgent care (UC) encounters among adults who were diagnosed with acute respiratory infection and tested for SARS-CoV-2 using polymerase chain reaction (PCR) during a (1) hospital admission or (2) ED or UC encounter without a subsequent hospital admission for the same index encounter.
The BNT162b2 XBB vaccine provided statistically significant additional protection against a range of COVID-19 outcomes during the early part of the 2023 to 2024 viral respiratory season.
The study included patients aged 18 years and older treated at Kaiser Permanente Southern California between October 10, 2023, and December 10, 2023.
updated vaccines play a crucial role in reducing severe disease and hospitalization.
Vaccine Makeup, The Changing Variants
Last September, the FDA amended the emergency use authorization of the Pfizer-BioNTech COVID-19 vaccine to include the 2023-2024 formula. That vaccine included a monovalent component that corresponded to the Omicron variant XBB15 of SARS-CoV-2. That vaccine (2023-2024 formula) was authorized for all doses administered to individuals 6 months through 11 years of age to prevent COVID-19.
It was used for the study, which was conducted during the fall of last year when the XBB strain was the dominant variant circulating in the United States. Earlier this year, the dominant strain was JN1, and when the FDA met recently to discuss the makeup of the 2024-2025 formula, they initially recommended a monovalent JN1-lineage vaccine composition for the formula, but federal officials updated their guidance, urging vaccine manufacturers to incorporate the KP2 strain, if feasible.2
The JN1 variant has given rise to a newer family of variants, called “FLiRT,” named after their mutations. These newer “FLiRT” variants have been so named based on the technical names for their mutations, one of which includes the letters “F” and “L,” and another of which includes the letters “R” and “T.”2
“The “FLiRT variants” is the term being used to describe these variants—including KP2, JN17, and any other variants starting with KP or JN—that appear to have independently picked up the same set of mutations. This is called convergent evolution. They are all descendants of the JN1 variant that has been dominant in the US for the past several months,” according to a recent report from Johns Hopkins Bloomberg School of Public Health.2
However, it is important to note with each new descendant, there is some variability in them that could potentially affect to some degree the efficaciousness of the vaccines.
Final Takeaways
The investigators point out that the utilization of updated vaccines—compared to older versions of the vaccine or no vaccination—helped significantly in the reduction of severe disease and hospitalization.1
"These 2 findings help reaffirm current recommendations for broad age-based use of annually updated COVID-19 vaccines,” the investigators wrote. 1
