Influenza and COVID: what are the risks of co-infection?

It is far from impossible to contract more than one respiratory disease at the same time. We know that co-infections are fairly common.– explains Rodica Gilka, medical consultant for the National Institute of Public Health Quebec (INSPQ).

According to Dre Gilka, up to 15% of patients hospitalized with respiratory viruses in Quebec have multiple infections that can lead to complications. However, very little is known about the possible consequences of infection with COVID-19 and influenza.

However, we must prepare for this opportunity, she said, due to the easing of health measures that will occur in the coming months. Social contacts will increase and the flu, among other things, may be beneficial.

Since the population has not encountered these viruses for several months, an ecological niche has been opened. We fear that the flu and other viruses will start circulating again in the population in the fall.

Quote from:Dr. Rodica Gilka, Medical Consultant at the National Institute of Public Health of Quebec

First clues

In his laboratory at the Center de recherche du CHU Quebec-based microbiologist and infectious disease specialist Guy Boyvin studied the interactions between the virus that causes COVID-19 (SARS-CoV-2) and the influenza (H1N1) strain for several months.

We wanted to see if the virus that multiplies can have a good viral load […] can affect another virus by interfering with the replication of the second virus.

To do this, he infected human nasal and bronchial cells, first with the H1N1 virus, and then with SARS-CoV-2. He also did the opposite, infecting cells first with SARS-CoV-2 and then with the H1N1 virus.

Although the results are preliminary, the results so far amazing, according to DR Boyvin: It looks like the first flu infection prevents the development of COVID-19.

The flu virus will almost completely block the multiplication of the COVID-19 virus.

Quote from:Dr. Guy Boyvin, microbiologist and infectious disease specialist at CHU de Québec

Dr. Guy Boyvin, microbiologist and infectious disease specialist at CHU de Québec.

Photo: Radio Canada

The H1N1 virus appears to secrete interferon, an antiviral molecule that inhibits the multiplication of another virus for several days.

However, the opposite is not true. When we start with COVID-19 infection followed by H1N1 virus infection, the COVID-19 virus does not interfere with the replication of the influenza virus., indicates the letter DR Boyvin.

What is the order of the vaccinations?

Based on these results, DR Boyvin allows himself to extrapolate what could happen in the coming years if COVID-19 becomes a seasonal virus like the flu.

If we start the season with a big flu epidemic, we expect COVID-19 to do little damage. On the other hand, if we start with a good COVID-19 epidemic, it will not prevent the flu epidemic from occurring at the same time., – he illustrates.

At this point, we could infect people with both viruses with much more dramatic consequences.

Quote from:Dr. Guy Boyvin, microbiologist and infectious disease specialist at CHU de Québec

With caution, he pondered what would then be the best strategy to protect the population from both diseases at the same time.

It would be plausible to say that we should get vaccinated against COVID-19 first and then flu.


Job DR However, Boyven has his limits. Using only the H1N1 virus, it is impossible to know how other strains of influenza interact with the virus that causes COVID-19.

Each season, not only H1N1 circulates, but also H3N2 and influenza B virus. To my knowledge, I have not yet seen any interactions between these other influenza virus subtypes and SARS-CoV-2, Analysis by Rodica Gilk.

Job DR Boivin also does not take into account other respiratory viruses that are neither influenza nor COVID, but which are nonetheless present and which may also interact with SARS-CoV-2.

Finally, the work was done on virgin cells that had never been exposed to the H1N1 virus or SARS-CoV-2. This means that immunity acquired through antibodies is not one of the variables of interest.

Once these limits have been established, INSPQ continues to evaluate the results DR Boyvin is very interesting, especially when you consider the scarce data on this fundamental question.

It provides us with additional elements that can help us make decisions.

Quote from:Dr. Rodica Gilka, Medical Consultant at the National Institute of Public Health of Quebec

Dre However, Rodica Gilka believes that the sanitary measures people are accustomed to during the pandemic, be it washing their hands or wearing a mask, will help better fight the flu in the coming years.

Our daily lifestyle can prevent not only SARS-CoV-2, but other viruses as well. […] This could help us fight this possibility of mixed infections, the severity of which is currently unknown.

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