Another study found that the effectiveness of the COVID-19 vaccine turned negative within months

Efficiency Pfizer and AstraZeneca COVID-19 vaccines show negative results against severe COVID-19 disease months after administration, according to a new study.

A single dose of Pfizer’s vaccine was pegged at minus 121 percent effective at day 84 and minus 85 percent effective at day 98. The second Pfizer dose held up better, but still fell below 50 percent on day 98, the researchers concluded.

One dose of the AstraZeneca vaccine tested negative on day 70, and the second dose on day 84, according to paperwhich was published in the International Journal of Epidemiology.

Negative efficacy means that a vaccinated person is more likely to experience a condition than an unvaccinated person.

Pfizer and AstraZeneca did not respond to requests for comment.

The researchers arrived at the estimates by analyzing the health records of approximately 12.9 million people in England, Scotland, Wales and Northern Ireland. The trial period ran from December 8, 2020, to June 30, 2021 — one of the reasons boosters, which were only available in late 2021, were not included in the study.

Steven Kerr, a senior research fellow at the University of Edinburgh’s Usher Institute, and other researchers theorized that the negative evaluations arose from behavioral differences between the vaccinated and unvaccinated populations.

“We believe the most likely explanation … is that vaccination caused recipients to believe they were protected, leading them to change their behavior in ways that increased their chances of infection,” they wrote. “These changes in behavior should have initially been outweighed by the protection offered by the vaccine-stimulated immune response, but as time went on, the protection probably waned so that the influence of the changes in behavior could become dominant.”

The researchers did not provide any evidence for the theory.

The group also said it is possible that the protection a person enjoys after recovering from COVID-19 may have played a role, pointing to one of many works who concluded that natural immunity is better than vaccination.

Part of a growing trend

The study is the latest to assess the vaccine’s negative efficacy, although others have examined efficacy against infection.

Researchers from Moderna said in recent work that the effectiveness of the vaccine against the infection became negative after several months against BA.2.12.1, BA.2, BA.4 and BA.5, which are all subvariants of the Omicron coronavirus variant.

Another paper, which analyzed the effectiveness of vaccines against infections among children aged 5 to 11 years, estimated that the Pfizer vaccine became negative after 18 or 20 weeks, depending on whether the children were also infected with COVID-19.

Researchers in Qatar, examining the effectiveness of Pfizer and Moderna vaccines, estimated in June that their effectiveness has become negative over time.

And another paper, this one published in May American scientists found that the effectiveness of Pfizer’s vaccine became negative after five months for children aged 12 to 15 years.