Today, JAMA Internal Medicine published a study calculating the protection offered by the latest Pfizer COVID-19 XBB vaccine compared to older vaccines against COVID-associated hospitalization and emergency department (ED) or urgent care (UC) visits.
The test-negative case-control study of the BNT162b2 XBB vaccine was performed among adults in the Kaiser Permanente Southern California health system from October 10 to December 10, 2023. XBB was the dominant strain of SARS-CoV-2 in the United States at that time but has since been supplanted by JN.1.
The study included patients who presented with an acute respiratory illness and had a positive SARS-CoV-2 polymerase chain reaction test and controls who had an acute respiratory illness but tested negative for SARS-CoV-2. A total of 2,854 cases and 15,345 controls (median age, 56) were included in the studies.
The authors compared outcomes among those who had received an updated XBB vaccine and those who had not received an XBB vaccine of any kind, regardless of prior COVID-19 vaccination or infection history.
"Receipt of prior (non-XBB) versions of COVID-19 vaccines was also compared with being unvaccinated to estimate remaining protection from older vaccines," the authors said.
62% protection against hospitalization
Compared to those who had not received an updated XBB vaccine, recipients had 62% protection against COVID-19 hospitalization (95% confidence interval [CI], 32% to 79%). Protection was 58% against ED/UC visits (95% CI, 48% to 67%).
A history of vaccination with pre-XBB vaccines did not significantly reduce the risk of COVID-19 outcomes, including hospital admission, and outcomes were similar to those of unvaccinated patients.
The median time between vaccination with a non-XBB vaccine and illness was 1 to 2 years, while the median time between vaccination with an XBB vaccine and illness was 34 days.
The combination of waning vaccine-induced immunity and continuous SARS-CoV-2 strain evolution eventually renders prior versions of vaccines ineffective.
"The present findings help reaffirm current recommendations for broad age-based use of annually updated COVID-19 vaccines in the US to improve protection against COVID-19 each year prior to likely winter peaks in disease activity," the authors concluded. "The combination of waning vaccine-induced immunity and continuous SARS-CoV-2 strain evolution eventually renders prior versions of vaccines ineffective."
In an invited commentary on the study, Gopi Mohan, MD, PhD, of the University of Texas MD Anderson Cancer Center, and others, write, "These findings illuminate the issue of waning immunity and point to the importance of regular boosting in addition to updating vaccine formulations."
