A recent study funded by Pfizer has found that all versions of the COVID-19 vaccine, except for the newest one, do not provide significant benefits compared to being unvaccinated. The study, conducted by researchers from Kaiser Permanente and led by Sara Tartof, analyzed data from Kaiser Permanente Southern California. The findings showed that individuals who received older versions of the Pfizer vaccine had a higher risk of outpatient visits and, for certain age groups, were more likely to be hospitalized with acute respiratory illness.
Out of the 24,007 encounters analyzed in the study, 4,232 involved patients who tested positive for COVID-19, while 19,755 involved patients who tested negative. The majority of both groups had been vaccinated, with only 2,717 individuals who had never received a vaccine. The researchers found that older versions of the Pfizer vaccine did not provide significant protection against hospital admissions, emergency department visits, urgent care visits, and outpatient visits.
However, the study did suggest that the newest version of the Pfizer vaccine, targeted at the XBB.1.5 virus strain, may confer protection. Among individuals who tested positive for COVID-19 and had acute respiratory infection, 4.1 percent had received the newest vaccine version. In contrast, among those who tested negative for COVID-19 and had acute respiratory infection, 7.4 percent had received the newest shot.
The odds ratios of a person who received the XBB vaccine being admitted to a hospital, entering an emergency department or urgent care, and visiting an outpatient facility were significantly lower than one. This means that the vaccine was associated with protection against all three types of encounters. Similar results were observed when comparing those who received the XBB vaccine to different populations, including those who received the Pfizer shot available from 2022 to the fall of 2023.
It is worth noting that the study has some limitations. It did not assess longer-term effectiveness, and the median time since receipt of an XBB shot among the study population was only 30 days. Additionally, conflicts of interest, including Pfizer funding, have raised concerns about potential bias in the reported results.
Experts have commented on the study, highlighting its limitations and the need for randomized, controlled trials to provide more robust data. Dr. Harvey Risch, a professor emeritus of epidemiology at the Yale School of Public Health, pointed out that the study's short follow-up period did not address the current circulating JN.1 variant, which emerged after the study data collection period. The authors themselves acknowledged the need for future studies to examine the association between the XBB vaccine and the development of strain-specific diseases.
