As if living with COVID-19 for nearly six months wasn’t enough, Minnesotans have another thing to worry about as the temperature drops and fall sets in: flu season.
Influenza, a serious respiratory virus in its own right, has killed between 40 and 440 Minnesota residents per year in recent years, sometimes taxing Minnesota’s hospital resources with patients fighting to breathe.
And that’s without the threat of the novel coronavirus, which has so far killed more than 1,800 Minnesotans this year.
It’s not clear yet how the flu and COVID-19 will interact together, experts say: the novel coronavirus hit much of the U.S. in March, at the tail end of this year’s flu season. But they worry that this flu season, the respiratory double whammy could put more lives in danger.
The devil we know and the devil we don’t
The seasonal flu is a devil we know: it’s believed to date back thousands of years, and may have been described by Hippocrates in writings from 410 BCE.
The human influenza virus was discovered by scientists in 1933, and researchers have been studying how the virus works, who is hardest hit and how to mitigate its effects ever since. Some years, such as when the A H3 influenza strain is dominant, the virus tends to be more severe than others, when, say, the A H1 strain is more dominant (the A refers to the strain — type A viruses can infect animals and humans, and H refers to hemagglutinin, a surface protein.
The flu has a short incubation period of between one and four days. It’s often described as hitting like a freight train, with symptoms like coughing, chills and fever that come on quickly. In severe cases, it can lead to pneumonia and acute respiratory distress syndrome, sometimes even affecting the heart and central nervous system. Flu kills in an estimated 0.10 percent of cases, or one in 1,000.
If the flu is a devil we know, COVID-19 is a devil we’re still learning about. A pneumonia caused by an unknown pathogen was first noted to the World Health Organization on Dec. 31. The new coronavirus’ genome was sequenced by mid-January, and it’s so far killed more than 860,000 people worldwide.
COVID-19’s incubation period is thought to be between two and 14 days, but people may be most infectious before they even show any symptoms, making them unwitting transmitters of the virus. On top of that, perhaps 40 percent of cases are asymptomatic, making it difficult to estimate mortality rates.
Like the flu, a severe case of COVID-19 can result in pneumonia and severe acute respiratory distress. But the virus can also attack the kidneys, the heart and liver.
Flu + COVID-19 effects unclear
While we know COVID-19 isn’t likely to go away by the time flu season’s in full swing, there’s a lot we don’t know about how COVID-19 and the flu interact together.
“Both are respiratory viruses that have the potential to do their own separate damage,” said Dr. Anne Liu, infectious disease physician with Stanford Health Care in California.
Data from China suggest that people who are coinfected with the novel coronavirus and the flu may experience worse disease than those who have one or the other, Liu said.
“That’s not surprising to us, and I hope it’s not surprising to the public,” she said. “They are pretty different viruses, they seem to do damage in somewhat different ways, but both can be more severe in people who are elderly, immunocompromised, and people who have comorbidities.”
Both viruses mainly manifest by attacking the lungs, but autopsy pictures of the lungs of patients who have died from each of the viruses show the two attack in different ways.
“Certainly it would be reasonable to expect that having both together could increase the risk of respiratory failure and death, compared to having one virus,” Liu said.
And while we don’t know yet what the effects of coinfection would be, Liu said that with the coming flu season, we’re, unfortunately, likely to find out.
COVID-19 precautions may slow flu spread
One of the big questions looming over the combined COVID-19-flu season is just how bad of a flu year we’re in for.
Early data from the southern hemisphere, where it is currently the tail end of flu season, suggest a more mild year, said Jennifer Heath, the education and partnerships unit supervisor for the Minnesota Department of Health’s Vaccine Preventable Disease Section. Influenza cases in southern hemisphere countries are down this year compared to years past.
That might be because of health precautions taken to slow the spread of COVID-19, such as social distancing, mask wearing and handwashing. (It could also partly reflect less flu detection: people may be more reticent to go to the doctor with flu symptoms due to fears of COVID-19 exposure, Liu said.)
Ahead of flu season, health officials agree that getting a flu vaccine is the most immediate precaution, apart from social distancing, masks and handwashing, most people can take to help prevent what could be a very dangerous flu and COVID-19 season this year.
“We have a vaccine for influenza and that is just our best bet in trying to tamp down respiratory disease this fall,” Heath said.
Even when the flu vaccine doesn’t prevent people from getting sick with the virus, it generally helps prevent more severe disease, said Dr. Michael Matthay, a professor of medicine at the University of California-San Francisco, in a web forum last week. Matthay said most patients who succumb to acute respiratory distress syndrome from influenza have not been vaccinated for flu.
On top of its benefits in fighting influenza, some studies that have yet to be peer-reviewed suggest the vaccine may be associated with decreased COVID-19 mortality.
If this is the case, Liu said, it’s not clear whether there is some causality there — that the flu vaccine helps the body fight COVID-19, or whether people who get the flu vaccine tend to better heed public health directives, and are therefore less likely to get sicker and die.
Needless to say, now’s a good time to get a flu shot.
It takes about two weeks for the flu vaccine to take effect. The Minnesota Department of Health’s flu surveillance reports start tracking the virus at the end of September. While case counts are usually low through the fall, they pick up as winter starts up.
“We don’t want people to wait around because you might miss your opportunity, or you might forget,” Heath said.