No, the flu vaccine has not been proven to increase the risk of catching Covid-19

As winter approaches, health professionals fear that an influx of seasonal flu patients should be added to that of Covid-19 patients. The president of the scientific council, Jean-François Delfraissy, a recommended to do “a civic gesture”, getting vaccinated. But many messages encourage people to refuse the vaccine. They rely on a study allegedly “to achieve within the American army”that the injection would increase the risk of catching Covid-19 by 36%.

What these publications say

UN article published on September 27 on the participatory platform Agoravox claims that a “interprofessional group of Belgian caregivers” launched an action in summary proceedings before the Brussels court to denounce “the surreal official recommendation of a mass vaccination against seasonal flu”. According to the same source, “a recent study (2020) carried out within the American army reports a risk of infection with the coronavirus increased by 36% for people who have received a vaccination against seasonal influenza”.

Screenshot price on the Agoravox website on September 28, 2020

A image shared on facebook rapporteur for the words of virologist Judy Anne Mikovits – known for her opposition to vaccination – takes up this figure. The American scientist also assures that “flu vaccines increase the risk of catching Covid-19 by 36%”.

Screenshot price on Facebook on September 30, 2020


A study prior to the appearance of SARS-CoV-2

These claims have been circulating for several months on websites american and french. They are taken froma study published in the journal Vaccine. Its author, Greg G. Wolff, is a researcher at the US Department of Defense. His work focuses on “viral interference”a phenomenon “still poorly understood that could cause certain viruses, or even vaccines, to influence the risk of contracting another viral infection at the same time”as summarized by the site of the Click Center, a Canadian association that promotes dialogue between scientists and the public.

Specifically, the study seeks to find out whether vaccination against influenza can increase the risk of catching other respiratory viruses. For this work, carried out in As part of the US Department of Defense’s Global Respiratory Pathogen Surveillance Program, nearly 9,500 samples were taken from members of the armed forces and their families to analyze for potential viruses.

The researcher then analyzed this data to find out whether vaccinated people had more respiratory illnesses than unvaccinated people during the same season. The results show, among other things, that 7.8% of people vaccinated against influenza contracted a coronavirus infection during the 2017-2018 winter season, compared to 5.8% of people who were not vaccinated.

However, SARS-CoV-2 only appeared at the end of 2019. “At the time of the study, and even at the time of initial electronic publication, Covid-19 did not yet exist”, insisted the author of the study in a note published after the start of the pandemic. He was, in fact, interested in four types of seasonal coronaviruses (229E, NL63, OC43 and HKU1) that cause colds, not SARS-CoV-2.

“It is not possible to say that vaccination against influenza increases the chances of catching Covid-19 since there was no mass vaccination in times of Covid”, summarizes Matthieu Revest, infectious disease specialist at the Rennes University Hospital.

An insignificant figure

To estimate the magnitude of the difference between two numbers, here 7.8% and 5.8%, epidemiologists use a statistical measure called the “odds ratio” (odds ratioin English), explains Pascal Crépey, epidemiologist and teacher-researcher at the School of Advanced Studies in Public Health in Rennes. This shows that vaccinated patients were 36% more than others to have coronavirus. However, this does not prove that the flu vaccine would increase the chances of catching a coronavirus, let alone the one responsible for Covid-19.

Screenshot of a table from Greg G. Wolff's study

Greg G. Wolff asserts that his research findings do not “not requiring the anti-seasonal flu vaccination view” and must, in fact, be interpreted” inversely », given that, overall, the vaccinated were less sick than the others: “Significant protection against influenza was associated with vaccination and a slight decrease in the risk of infection with other respiratory viruses was also found. » The slight differences observed, as for coronaviruses, are not statistically conclusive.

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“Many different viruses were tested in this study. However, there is a classic mechanism in statistics which is that the more you test, the more chance you have of finding something without it being statistically significant., warns Pascal Crépey. In addition, the study did not aim to examine the levels of risk of vaccinated or unvaccinated populations in the face of the coronavirus. The figure of 36% is put forward by opponents of the flu vaccine, but it does not take into account the factors of age and season, which are nevertheless of capital importance in terms of epidemics due to respiratory viruses.

It is therefore not possible to establish causality from these figures, that is to say a link of cause and effect, even if there is indeed a correlation and that these data seem linked. Many phenomena can thus be correlated, without one being the cause of the other.

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The flu vaccine, an indirect weapon against Covid-19

“To say that immunity against influenza would have an effect on other respiratory infections is only a hypothesis that has never been scientifically proven”would like to remind Matthieu Revest, of the Rennes University Hospital.

In one communicated published in May, the National Academy of Medicine recalls that this vaccine is ” essential to protect the population against a severe seasonal influenza epidemic”. With the particular objective, this year, of facilitate doctors’ diagnoses avoiding confusion between Covid-19 and the flu which have quite similar symptoms. This could make it possible to limit unnecessary screenings, while many laboratories are already crowded, and “reduce the hospital burden”concluded Pascal Crépey.

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