COVID-19 vs. flu: How to tell them apart

Influenza viruses become widespread each year beginning as early as mid-fall and running as late as mid-spring. This coming year's influenza season will also compete with COVID-19.

The virus that causes COVID-19, SARS-2-CoV, can cause symptoms that are similar to influenza: fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headaches, sore throat, congestion or runny nose, nausea or vomiting and diarrhea.

So how can someone tell the difference between influenza and COVID-19?

The short answer is to test for influenza virus and for SARS-2-CoV virus. The long answer is that it depends on how much virus is circulating in the community and other risk factors.

Influenza is more likely when there is a lot of influenza circulating in the community. For example, during March 2020, influenza would have been more likely because there were a lot more people infected with that virus than COVID-19. On the other hand, in April and May 2020, there were few to no patients with influenza and a lot more people infected with COVID-19.

What are some characteristics of each virus?

• Symptoms. The influenza virus can create mild to severe symptoms. COVID-19 can be asymptomatic, mild or have severe symptoms.

• Contagious period. Influenza virus can be contagious a day prior to symptoms and last a few days on average. SARS-2-CoV virus can be contagious two days prior to symptoms and last until 10 days after the onset of symptoms. Asymptomatic individuals can transmit infectious virus for no more than 10 days.

• Complications. Risk for severe COVID-19 infection is higher for adults, rising with age, obesity and chronic medical conditions. Pregnancy is also a risk factor for severe influenza infection. Unlike influenza, COVID-19 infection can trigger inflammation in the lungs days later.

• Testing. This year everyone who is sick needs to be tested. Without a test, there is no way to tell if it is influenza virus, another respiratory virus or COVID-19.

• Recovery. Influenza patients may recover at home and go back to work or school as soon as they have no fever for one day. COVID-19 patients need to stay in isolation for 10 days, and all their close contacts need to stay in quarantine for 14 days.

• Vaccine. There are multiple FDA-licensed influenza vaccines produced annually to protect against the three or four flu viruses that circulated in the previous year. This year is more important than any other year to get the influenza vaccine.

While people can still get the flu if they are vaccinated, during most years it provides at least 70 percent protection from getting the flu.

The Centers for Disease Control and Prevention recommends that all people 6 months and older get a yearly flu vaccine. September and October are good times to get vaccinated. However, as long as influenza viruses are circulating, it's still worth it to get vaccinated, even in January or later.

COVID-19 vaccines are still being developed. Until they are widely available, most people have no immunity to the virus. The only defense is keeping away from others who are infected.

If everyone does the right things to keep COVID-19 away - by wearing masks, washing their hands and keeping physically distant ­- they might not have to get sick from influenza either.