Everything you need to know about flu strains and how they mutate

Sherif Beniameen Mossad, MD

What is commonly called ‘the flu’ is actually a collection of potentially dangerous influenza virus strains that mutate over time, making it important to have an annual flu vaccination alongside practicing everyday prevention techniques, such as proper hand washing, says an expert from global health system Cleveland Clinic.

“What all flu strains have in common are the symptoms they cause,” infectious disease doctor, Sherif Beniameen Mossad, MD, says. “Fever, headache and a cough are the three cardinal manifestations of all flu viruses.”

According to the World Health Organization (WHO), influenza activity has started to increase in many countries.  The body states: “Public health measures taken to reduce transmission of COVID-19, also reduced influenza activity. Now that these measures have been removed, both viruses may transmit more easily.” Similarly, the Centers for Disease Control and Prevention (CDC) in the U.S., where Dr. Mossad practices, has also noted increased seasonal flu activity.

Dr. Mossad explains that there are three types of flu viruses that affect people. They are known as influenza viruses A, B and C. Influenza A and influenza B viruses cause the most severe illness and lead to widespread outbreaks. Influenza C viruses cause mild illnesses in humans and animals, are closer to a common cold, and are not detected by the commonly used flu tests.

Of the two we know as ‘the flu’, influenza A viruses are the most common and are the cause of seasonal flu outbreaks or epidemics, as well as global flu pandemics. Influenza A viruses can affect both humans and animals, and examples of this type of flu are the 1918 Spanish flu pandemic and the 2009 H1N1 pandemic (also known as ‘swine flu’).

Influenza B viruses, on the other hand, affect only people, not animals, and they do not spread to the point of pandemics. Influenza B viruses are more likely to make a person sick later in the flu season compared to influenza A.

How do vaccines keep up with mutations? 

According to Dr. Mossad, there are two types of flu virus mutations. The first, antigenic drift, refers to the small ways in which the flu virus mutates each year and is the reason for annual flu epidemics. The second is antigenic shift, which is a ‘tidal wave’ of flu virus mutation, or the introduction of novel flu strains to humans from animals; usually pigs or birds.

“Antigenic shift is when viruses change so much that you wind up with a virus that humans have never been exposed to at all,” Dr. Mossad says. “That’s what happened in 2009 with the H1N1 swine flu virus. It was an entirely new virus to humans, so no one had built up any immunity to it at all.”

Each year, the WHO monitors trends to determine the strains of flu that will be most common, and each country makes its own decision about which viruses should be included in flu vaccines licensed there. The flu vaccine is then created to protect individuals from what these experts expect will be the most prevalent influenza A and influenza B viruses for that flu season.

Protect yourself from the flu

In addition to getting a vaccination, Dr. Mossad suggests these best practices to stay healthy this flu season:

  • Practice good hand-washing hygiene. Wash your hands thoroughly with soap and water. If you aren’t able to use soap and water, use an alcohol-based hand sanitizer.
  • Avoid being around other people when you don’t feel well, especially when you have a fever.
  • Avoid being around people who are sick whenever possible.
  • Avoid touching your eyes, nose and mouth.
  • Eat well, exercise and get enough rest.
  • Consider taking a multivitamin and possibly vitamin D supplements to support your immune system.