When COVID-19 meets the flu

Just as scientists are scoring successes in coronavirus research, new problems are on their way. Fall is with us and winter is around the corner, so the season for colds and flu has begun — joining COVID-19.

The coronavirus is already new territory for science, and the effects of its combination with influenza are equally unknown. There is much speculation about what is to be expected and what will or could happen when these two dangerous infectious diseases come together. This is what is making it so difficult to prepare adequately for the cold time of year.

Coughing, sniffles and hoarseness in fall and winter are nothing new, and flu is also a regular feature of these seasons. But we can be vaccinated against it, and that is of advantage in diagnosing cases of coronavirus as well.

"If people who have been vaccinated against influenza still have flu symptoms, it is more likely that it is not influenza," says Gerárd Krause from the Helmholtz Centre for Infection Research in the northern German city of Braunschweig. "This, in turn, makes it easier to decide matters regarding home quarantine and getting a clear diagnosis."

Influenza vaccination

A flu vaccination may thus be able to narrow down the diagnostic options when flu-like symptoms occur, but whether such a vaccination also has an influence on the behavior of the dangerous new virus is — like so much else — not clear. "It is conceivable that there is an indirect effect. But it is, I believe, a matter of speculation whether it has an immunological effect in the narrower sense,” says Krause.

Every winter, doctors' waiting rooms are full of people who are coughing and sniffing but who mostly turn out to have only a severe respiratory infection. According to current knowledge, the virus that causes COVID-19, SARS-CoV-2, is also likely to be subject to seasonal fluctuations. 

In winter, cold viruses, at least, flourish because cold and dry air offers ideal conditions for their spread. In addition, it becomes more difficult to air rooms regularly and intensively — an important further measure to counteract the coronavirus and contain to some extent the danger posed by aerosols.

According to the Robert Koch Institute, Germany's public health agency, between 5% and 20% of people in Germany become infected with flu viruses every year. These viruses are also dangerous and can be fatal. The flu vaccination must be adapted to the influenza viruses every year, because they mutate. But at least there is a vaccination.

Most experts agree that there is unlikely to be a vaccine against the coronavirus by the time the next wave of influenza comes around. And even if a vaccine were to be approved, many unknowns remain.

COVID-19 and flu in double pack

For example, there is a lack of practical experience in dealing simultaneously with SARS-CoV-2 and influenza. It is possible to speculate that having influenza could facilitate the entry of the coronavirus into the human body. "The general weakening of the immune system during an influenza infection could increase the susceptibility of a patient to a SARS-CoV-2 infection," Krause says.

However, it is uncertain how dangerous this double infection could ultimately be and what can be done about it. Krause is of the opinion that we must arm ourselves against all three diseases — colds, flu and COVID-19. If we have a cold, bed rest, hot tea and cough medicine usually help. We can get vaccinated against flu. But how do we deal with COVID-19?

Probably people can only hope that if they get the illness, they will have a mild form with as few after-effects as possible. Here, it will certainly help to stick to suggested rules on hygiene to reduce or prevent our exposure to the virus. In an interview with DW, Bonn-based virology professor Hendrik Streeck made it clear that COVID-19 usually takes a more severe course when there is a high viral load at infection.

Hygiene, hygiene, hygiene

The same hygiene measures with which we are trying to get at least some kind of grip on COVID-19 also apply to influenza. The less we come into contact with viruses, the greater the chance that we will be spared an infection or that it will be mild.

These measures include general hygiene precautions such as frequent hand washing and the wearing of protective face masks. "The various hygienic measures against COVID-19 will also reduce the spread of influenza," says Krause. "Possibly, further connections of a more immunological nature will be discovered."

Let us hope that is the case, because the flu season hasn't even started.