People Who Received Older Pfizer COVID Vaccines Had Similar Outcomes as Unvaccinated: Study


Pfizer-funded study finds no benefit for all vaccines except for the newest version.

People who received any version of Pfizer’s COVID-19 vaccine except for the newest one were no better off than the unvaccinated, according to a new paper.

“Compared to the unvaccinated, those who had received only older versions of COVID-19 vaccines did not show significantly reduced risk of COVID-19 outcomes, including hospital admission,” Sara Tartof of Kaiser Permanente and her co-authors wrote.

Analyzing recent data from the Kaiser Permanente Southern California, Ms. Tartof and colleagues found that people who received at least two doses of older vaccines actually had a higher risk of outpatient visits and, for some age groups, were more likely to be hospitalized with acute respiratory illness.

The median time since receipt of the most recent dose among the people who were vaccinated but did not take the newest version was 363 days.

Ms. Tartof and Pfizer, which funded the study, did not return requests for comment.

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The study analyzed acute respiratory encounters in the health system and excluded a number of patients, including those who received a new COVID-19 vaccine that was not made by Pfizer.

Out of 24,007 encounters left, 4,232 involved patients who tested positive for COVID-19 and 19,755 involved patients who tested negative.

The vast majority of both groups were vaccinated, as the study population included just 2,717 people who never received a vaccine. Researchers, as is typical during the pandemic, only counted a person as vaccinated if at least 15 days had elapsed since a dose was administered.

Researchers found that doses of older vaccines did not seem to protect against hospital admission, emergency department or urgent care visits, and outpatient visits in a meaningful way.

The results did suggest that receipt of the newest Pfizer shot, targeted at the XBB.1.5. virus strain, may confer protection.

Of the people who had acute respiratory infection and tested positive for COVID-19, 4.1 percent had received the newest vaccine version. Of the people who had acute respiratory infection and tested negative for COVID-19, 7.4 percent had received the newest shot.

The odds ratios of a person who received an XBB dose being admitted to a hospital, entering an emergency department or urgent care, and visiting an outpatient facility were much lower than one. That means the vaccine was associated with protection against all three types of encounters. The odds ratios were developed by comparing the XBB-vaccinated to all other patients, including unvaccinated ones.

Similar numbers were arrived at when comparing those who received an XBB dose to different populations, including those who received the Pfizer shot that was available from 2022 to the fall of 2023.


The XBB shots from Pfizer and Novavax were cleared by the U.S. Food and Drug Administration despite there being no human data. Moderna’s shot was cleared with data from just 50 people.

Observational studies like the new paper from Kaiser Permanente researchers can help fill the data gap, but many experts say they are inferior to randomized, controlled trials.

The Pfizer-funded researchers said that the results of the new paper “reaffirm current recommendations for broad age-based use of annually updated COVID-19 vaccines given that (1) XBB1.5-adapted vaccines provided significant additional protection against a range of COVID-19 outcomes and (2) older versions of COVID-19 vaccines offered little, if any, additional protection, including against hospital admission, regardless of the number or type of prior doses received.”

Limitations of the paper include not being able to assess longer-term effectiveness.

Median time since receipt of an XBB shot was just 30 days among the study population.

Ehud Qimron, a professor at Tel Aviv University’s Department of Clinical Microbiology and Immunology, told The Epoch Times in an email that the conflicts of interest reported, including the Pfizer funding, “reveals a strong bias, potentially influencing the reported results.” Mr. Qimron was not involved in the research.

Dr. Harvey Risch, professor emeritus of epidemiology at the Yale School of Public Health, who was also not involved with the study, said that the study was weak because as the pandemic has gone on, many people who experience colds and other symptoms do not test for COVID-19, or only test at home.

He also took issue with the short followup.

“The study observed patients over the initial two-month Kaiser Permanente roll-out of the XBB vaccine,” he said. “While the COVID booster vaccines can show some temporary reduced risks of infection, this effect wanes quickly and the authors’ data essentially did not address the current circulating JN.1 variant.”

JN.1 did not begin circulating until mid-November 2023, and the study only covered data through Dec. 10, 2023. The authors said that most of the cases analyzed “were likely XBB sub-lineages,” though they acknowledged a lack of genotype information.

“Thus, future studies describing the association between receipt of XBB1.5-adapted vaccines and development of strain-specific BA2.86 sub-lineage-related disease (e.g., JN.1),” they said, “are needed.”


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