There are several types of influenza viruses, and just like we have seen with COVID-19, they can change and mutate over time. If you catch the flu one year, you can catch it again the next year – because it may be a different virus that is circulating, or the virus has changed enough that your body doesn’t recognize it and your antibodies don’t work against this new or mutated version.

There are three types of influenza viruses that affect humans:

• Type A: Type A influenzas affect both people and animals, such as birds. The animals help spread the virus. Type A cases of influenza cause most flu pandemics or epidemics. In 1918, the world was hit by a flu outbreak that killed millions of people. Experts were worried that the H1N1 virus in 2009, what was called “the swine flu” by many, would have similar outcomes. Luckily, it did not. The virus did spread rapidly, but it was not as deadly as feared.
• Type B: Type B influenzas do not infect animals and do not cause epidemics or pandemics, but they can still cause serious harm to humans. 
• Type C: Type C influenzas are milder than either types A or B. They do not cause epidemics or pandemics, and they only affect humans.

Influenza A types, such as H1N1, are named by their proteins, hemagglutinin (“H”) and neuraminidase (“N”). There are 16 H proteins and 11 N proteins in all. The virus name depends on which hemagglutinin and neuraminidase are present in the virus. You can have any combination, such as H6N2 or H15N9.

Seasonal influenza, caused by both type A and B, is the most commonly known flu type. The severity of illness and the number of deaths caused by the flu varies quite a bit from year to year, depending on how strong the virus is. For example, an estimated 34,200 people in the U.S. died during the 2018/19 flu season, according to the Centers for Disease Control and Prevention (CDC). The year before, there were 61,000 flu-related deaths. A combination of factors lead to the number of deaths, including how well the virus is transmitted, how many people are vaccinated, and how effective the vaccine is for that year’s main flu strain.

A bout with influenza can make you feel really sick – fatigued and sore. For most people, you should begin to recover after a week or two, although it could take several weeks before you are back to feeling like yourself again. However, the flu can cause severe complications and even death for some people. Complications can range from secondary bacterial infections (infections that occur as a result of the flu) to dehydration, to sepsis, which can be fatal.

If you think you have the flu, you should check with your doctor or nurse practitioner to see if you should be treated with antiviral medications. This should be done as soon as possible. To be effective, the drug you are prescribed must be taken within 48 hours after the symptoms begin.

If you are not at high risk of developing complications or you are outside the window for an antiviral medication, your doctor or nurse practitioner may tell you to manage your flu symptoms at home but to go to the emergency room if you seem to get worse or develop new symptoms.

At-home care for flu symptoms means:

• Rest. Stay in bed to let your body restore itself and prevent spreading your infection.
• Drink a lot of fluids. It is easy to become dehydrated when you have the flu. These should be water and clear fluids, such as broths.
• Take over-the-counter medications, such as acetaminophen or ibuprofen, if you are allowed to. If the sick person is a child or teen, do not give aspirin because of a rare but fatal complication that can occur, called Reyes syndrome. Over-the-counter cold-and-flu remedies are not recommended for children under the age of six years, as per the FDA.

Most importantly, get your annual flu vaccination. Getting a vaccination is your best protection. Vaccines help reduce your risk of catching the virus – up to 60% some years. If you can’t get the vaccine for health reasons, encourage your family members, friends, and coworkers to be vaccinated. If they reduce their risk of getting the flu, your risk of catching it becomes lower.

Viruses want to stay alive. To do this, they adapt to their surroundings, sometimes finding ways to avoid the vaccines we develop. This happens with both the flu and COVID-19 viruses. Every year, a new influenza vaccine is developed based on information about the new influenza strain circling the globe. Scientists study which flu strains affect people and base each year’s vaccine on these strains.

People who are vaccinated but still contract the flu usually have fewer or less severe symptoms than those who are unvaccinated. They also have a lower risk of developing complications, like sepsis. According to the CDC, vaccinated adults have a significantly lower risk of being admitted to the intensive care unit (ICU), spend fewer days in the hospital if they do become too ill to stay at home, and have a lower risk of death.

Although it’s not possible to guarantee 100% protection, influenza can often be prevented with a few simple precautions:

• Hand washing is the number one weapon against influenza. Washing your hands after touching potentially contaminated objects (such as door handles) has been proven to effectively reduce the chances of you catching the flu. If you have the flu, washing your hands after touching your face can keep you from spreading the virus to others.
• Sneezing or coughing into your elbow is a good way to reduce flu virus transmission. Unlike sneezing or coughing into your hand, your elbow won’t touch common objects that others will touch.
• Wearing a mask if you are in a crowded area or you are near people who may have the flu.
• If you have the flu, avoiding others while you have symptoms and for 24 hours after the symptoms have gone away.
• Eating a healthy diet. Malnutrition, not consuming enough nutrients for your needs, can lower your body’s ability to fight infection.

Influenza and COVID-19 are two separate viruses, but they both affect the respiratory system. It is easy to confuse the two because their initial symptoms are similar:

• Cough, shortness of breath
• Sore throat
• Runny or stuffy nose
• Fever
• Muscle aches and pains
• Headache
• Vomiting

Children with the flu may have diarrhea, but both children and adults can get it with COVID-19. One symptom that only occurs with COVID-19 is the loss of taste and/or smell.

Testing is necessary because early treatment of both viruses can lessen the symptoms’ severity. Without testing, it’s not possible to know which virus you have.

Experts encourage people to get their seasonal flu vaccine to avoid a so-called “twindemic.” They are concerned that influenza cases and COVID-19 cases can peak at the same time during the traditional flu season. This is a particular worry for people who are at higher risk of catching either virus, such as the elderly and very young children, as well as people who have chronic illnesses or who are immunocompromised. However, it is also a concern for people who are healthy and have no medical problems.

The fears are two-fold. If you get the flu, your immunity drops as your body fights the infection. This makes you more vulnerable to catching COVID-19. It’s also possible to have both viruses at the same time. People who contract the viruses together are at higher risk of getting sicker.

Visit the CDC website for the most up-to-date COVID-19 vaccination schedule, which may vary depending on your age or personal risk. The CDC also recommends that everyone 6 months and older receive their flu vaccine by the end of October or as soon as possible every year.

Celebrities like actor Mary Louise Parker and professional tennis player Ken Flach developed sepsis when they had the flu. Learn about more celebrities who had sepsis here.