Novel and Variant Influenza Viruses

Influenza (flu) is a respiratory illness caused by the influenza virus that can infect both humans and animals. There are four types of influenza viruses: A, B, C, and D.  Influenza type A and B viruses commonly spread in people and are responsible for seasonal flu cases and seasonal epidemics in humans each year. Influenza A viruses are the only influenza viruses known to cause flu pandemics (i.e., global epidemics of flu disease).

There are some Influenza type A viruses that circulate in wild and domestic birds, swine (pigs), horses, dogs, and bats that do not commonly cause illness in humans but do cause sporadic cases each year. These are called variant influenza viruses. Human infections with variant influenza virus are rare, but when they do occur, it is typically in humans with close contact with sick animals or due to a change in the virus. These variant influenza viruses do not typically pass well between humans. Most people who become sick with a novel or variant flu virus from animals will have similar symptoms and recovery to seasonal flu and will not pass the virus to other humans.

How do influenza viruses change?

Flu viruses are constantly changing. The changes can happen slowly over time or suddenly. Sometimes, the changes result in viruses that spread more easily from animals to humans. Flu viruses can change through two methods called antigenic drift and antigenic shift:

  • Antigenic drift is when changes to the flu virus happen slowly over time. It happens with both influenza A and influenza B viruses. The changes happen often enough that your immune system can’t recognize the flu virus from year to year. This is why flu vaccination is encouraged yearly.
  • Antigenic shift only affects influenza A viruses and is a sudden, major change in the flu virus. This occurs when two flu viruses combine to form a virus with a new subtype or a mix of genes (including some from animals) that is very different. An example of this shift occurred in 2009 when an influenza A H1N1 virus with swine, avian, and human genes emerged in the spring and caused the first pandemic in more than 40 years.

In the case of novel flu, the goals of an outbreak investigation are to identify the source of the infection in people, to determine if person-to-person transmission of the virus is occurring, and to mitigate the spread of the virus in people and animals.

General Precautions

The best way to prevent infection from a variant or novel influenza virus is to stay away from sick animals such as poultry or swine. Other activities that may be performed to prevent catching any type of respiratory disease infection include:

  • Hand washing and using alcohol-based hand sanitizers,
  • Covering your coughs and sneezes with a disposable tissue or your arm or sleeve,
  • Avoiding touching your eyes, nose, or mouth,
  • Avoiding close contact with persons who are ill, and
  • Staying home when you are ill

People at high risk of serious complications from variant and novel influenza include children less than 5 years, adults 65 years and older, pregnant people, and people with certain chronic medical conditions like asthma, diabetes, heart disease, and weakened immune systems.

For more information on national influenza tracking, including novel and variant flu, visit the CDC’s webpage: Seasonal Flu and variant flu CDC surveillance and tracker: Weekly U.S. Influenza Surveillance Report | CDC

For information on seasonal influenza, respiratory syncytial virus, and other viral respiratory diseases in Georgia, please visit the DPH page:

Avian Influenza Virus (Bird Flu)

Swine Influenza A Virus (Swine Flu)

Page last updated 11/16/2023