Danish study shows negative vaccine effectiveness

Posted originally on TrialSite New by Staff on January 12, 2022

Danish study shows negative vaccine effectiveness

Researchers at the Statens Serum Institut in Denmark published a pre-print study suggesting that the second doses of Pfizer and Moderna vaccines may increase people’s likelihood of infection after 90 to 150 days. The same study suggested that a third Pfizer shot re-establishes efficacy for an indefinite period.

The large number of so-called breakthrough infections after second doses of vaccines suggest that vaccine clinical trials may have badly miscalculated efficacy rates.

The Danish Study

The study, which was published in December on the Medrxiv pre-print to await peer-review, explores SARS-CoV-2 protection against infection by the Omicron or Delta variants five months after one dose of the Pfizer or Moderna vaccines.

Lead author, Dr. Christian Holm Hansen, assistant professor of Medical Statistics and Epidemiology at the London School of Hygiene and Tropical Medicine, and his co-authors are affiliated with the Department of Infectious Disease Epidemiology and Prevention and the Department of Infectious Disease Preparedness, Statens Serum Institut, Denmark. The study received no external funding. 

The authors extracted data of positive polymerase chain reaction, or PCR, test results, and vaccination data from Danish registries between November 20 and December 12, 2021. The authors compared the rate of COVID-19 infections, of both Omicron and Delta variants, in unvaccinated individuals with those who received two doses of the Pfizer or Moderna vaccines.

By December 12, there were 5,767 Omicron cases in Denmark. Researchers discovered that vaccine effectiveness against Omicron was 55% and 37% for Pfizer and Moderna respectively. Vaccine efficacy waned rapidly over five months.

Initially, vaccine effectiveness was 87% for Pfizer and 88% for Moderna against Delta but decreased over the five months, to 54% and 65% respectively. 

The study found that VE was re-established after a Pfizer booster vaccine to 55% against Omicron and 81% against the Delta variants. The authors determined they lacked similar data about Moderna. 

Controversially, the authors found negative vaccine efficacy – a higher likelihood of infection – against Omicron during the period between 90 and 150 days after vaccination. The authors calculated Pfizer’s vaccine efficacy at -76.5% and Moderna’s at -39% during that period for Moderna. 

“The negative estimates in the final period arguably suggest different behavior and/or exposure patterns in the vaccinated and unvaccinated cohorts causing underestimation of the VE,” the authors said implying that unvaccinated people may have behaved more cautiously and exposed themselves to less risk or that more vaccinated people got tested for COVID-19 or engaged in behaviors that exposed themselves to more risk.

Data from the UK’s Office for National Statistics (ONS) shows that fully vaccinated people and those having received a booster vaccine are more than four times as likely to test positive for Omicron than the unvaccinated. Although this data is provisional, it supports claims that Omicron is evading vaccines. The data does not show anything about the severity of the Omicron cases, or whether the vaccines protect against serious infections and severe symptoms. 

Reuters fact-checked ONS’ data and claimed it does not show that vaccinated people are more likely to be infected than unvaccinated but only the probability of an infected person being infected with Omicron. “This means it doesn’t tell us that vaccines are making things worse overall, only that they are making it much more likely that a vaccinated person is infected with Omicron.”

A different pre-print paper titled “The BNT162b2 mRNA vaccine against SARS-CoV-2 reprograms both adaptive and innate immune responses” concluded that the Pfizer vaccine is causing immune system dysregulation. The paper concludes that the Pfizer vaccine reprograms innate immune responses “may contribute to a diminished innate immune response towards the virus.”

Are vaccines making us more vulnerable?

Because the Danish paper is still in preprint and awaiting peer review it is not conclusive. The study also looked at a small cohort of people in Denmark using publicly available data and lacks scale.

Negative vaccine effectiveness could be due to different behaviors or exposure patterns in vaccinated and unvaccinated individuals, resulting in an “underestimation of the vaccine’s effectiveness,” according to the authors, or because Omicron is highly transmissible and spreading rapidly. Dr. Astrid Blicher Schelde from the Statens Serum Institute, and one of the authors of the study, wrote an email to PolitiFact offering additional reasons including higher testing rates among vaccinated than unvaccinated people. Schelde also said that data from early Omicron cases might be skewed by international travelers’ more cautious behavior by unvaccinated. 

Schelde said vaccinated people are not necessarily more likely to be infected with Omicron more vaccinations and booster doses are required to combat Omicron and other COVID-19 variants. 

The UK Health Security Agency also reported zero or negative vaccine from a double dose of AstraZeneca, Pfizer, and Moderna vaccines after five months. A booster dose increased vaccine effectiveness to 40-60%. The report warned that these results should be interpreted with caution, due to low counts and possible biases related to populations with high exposure to Omicron.

A Norwegian paper published by Euro Surveillance in December 2021 also reported negative effectiveness of vaccines against as Omicron. The Norwegian case study focused on one “super spreader” event, where guests to a Christmas party became infected with Omicron. The authors suspected this high level of transmission between fully vaccinated people was due to the indoor location, crowding, and loud talking.

Should we be concerned?

Although the authors of the Danish study explained the reason for the negative vaccine effectiveness found in their study, other studies produced similar results with the effectiveness dependent upon booster vaccinations.

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