In the United States, influenza, commonly known as the flu, typically occurs between January and February. However, seasonal flu activity can last from fall through spring, spanning the months of October through May. Most Americans know of the flu as a common illness, hardly a rare disease. Despite its annual occurrence, the development of a new flu strain is always unpredictable.
Why do influenza viruses mutate?
The influenza virus is a virus that undergoes an incredible amount of change every year. A new flu strain can develop
in the following ways:
- Antigenic drift refers to the small, gradual changes that occur to viruses, causing new flu strains to be created. As increasing amounts of new flu strains appear, antibodies can no longer recognize the older virus, causing reinfection to occur. This is the main reason that people get the flu multiple times throughout their lives, or even during one standard flu season. Both influenza type A and type B viruses can undergo antigenic drift.
- Antigenic shift refers to abrupt, substantial change in influenza A viruses, resulting in new proteins in influenza viruses that infect humans. The shifts tend to migrate from an animal population to a human population, meaning that humans generally don't have any immunity to this novel virus. Unlike antigenic shift, antigenic drift occurs only occasionally, such as with the H1N1 virus of 2009.
Whether new flu strains are caused by antigenic drift or antigenic shift, nurses should be aware that many symptoms caused by either of these changes will lead to a similar symptoms. Patients will almost always have the standard symptoms such as coughing, fever, sore throat and runny nose. If a patient has been hospitalized for a severe respiratory illness, they should undergo testing to rule out specific diseases. This is particularly relevant to those individuals who have recently traveled to a country where antigenic shift strains are abundant. Nonetheless, it is unlikely that a patient residing in the United States would have a new flu strain.
How can we prevent new flu strains from spreading?
According to the Centers for Disease Control (CDC)
, three kinds of flu viruses circulate in the United States:
- Influenza A (H1N1) viruses
- influenza A (H3N2) viruses
- Influenza B viruses
Every year, these three viruses are used to produce seasonal influenza vaccines: trivalent and quadirvalent influenza vaccines. The trivalent flu vaccine offers protection from two influenza A and one influenza B virus, while the quadrivalent flu vaccine provides defense against two influenza A and two influenza B viruses. The appropriate vaccine for a patient can generally be determined based on their age and prior health conditions. Some flu vaccine options are available for this upcoming flu season.
This winter's (2013-2014) trivalent influenza vaccine is made from the following three viruses:
- an A/California/7/2009 (H1N1)pdm09-like virus
- an A(H3N2) virus antigenically like the cell-propagated prototype virus A/Victoria/361/2011
- a B/Massachusetts/2/2012-like virus
As recommended by the CDC, the quadrivalent vaccine should include those three viruses previously listed along with a B/Brisbane/60/2008-like virus.
By keeping tabs on all mutations of the influenza virus and utilizing the appropriate vaccinations, we can help prevent new flu strains from spreading throughout our communities.
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