Flu season is unpredictable. Over a period of 30 years, between 1976 and 2006, annual estimates of flu-associated deaths in the United States ranged from a low of about 3,000 to a high of about 49,000 people.
The severity of a flu outbreak can vary widely from one season to the next, depending on many things, including:
- what flu viruses are spreading
- how much flu vaccine is available
- when the vaccine is available
- how many people get vaccinated
- how well the flu vaccine is matched to flu viruses that are causing illness
Despite the severity of last season, the current flu season so far has been mild. Compare December 2014, when a few thousand cases were reported each week, to December 2015, when only several hundred cases were confirmed per week, according to the Centers for Disease Control and Prevention (CDC) flu surveillance system.
Usually, the later the flu season starts, the milder it is because there is simply less time that viruses are circulating in the environment. However, according to Dr. Joseph Bresee, chief of epidemiology in the flu division at CDC, it is still too soon to call this a mild flu season.
Recent years have been pretty bad, so this flu season could end up looking good by comparison, or the number of flu cases could catch up with those of previous seasons. The classic scenario is for the first flu cases to start to appear in the U.S. in October or November. Then the pace picks up in January and peaks in February or March.
Whether this will be a mild or severe flu season remains to be seen. With the two peak months ahead, it is still too early to tell.
Bresee recommends that everyone who has not had a flu shot get one immediately, given the likelihood that cases of flu will continue to increase over the next several weeks. People usually receive the vaccine when it is first available in their area (i.e., September), but getting it now will still provide weeks to months of protection.
So far, the viruses seen in the UD and other countries look very much like the vaccine strains, but while this is reassuring, mutations could still emerge. Normally, each February the World Health Organization (WHO) recommends the three or four flu strains to include in next year's flu shot.
Last year, mutations in an H3N2 strain of the virus were detected in circulation after the vaccine had already been made. So, although H3N2 (a dead version) was present in the flu shot, the 2014-2015 flu shot only reduced the risk of getting the flu by about 20 percent. In a good year, that rate is closer to 60 percent.
According to Michael L. Jackson, an associate scientific investigator at Group Health Research Institute in Seattle, although this year's vaccine is matching the most common strains so far, there have not been enough flu cases to date to predict which virus will dominate this season.
A recent study suggests there could be another aspect in identifying which flu viruses are in circulation. Researchers looked at flu spread among 84 people in Hong Kong during the 2009 flu season. They found that, although H1N1 and H3N2 were predominant, individuals were also getting infected at the same time with other, less common viral strains, suggesting that these minor strains can persist in the population and may even become predominant.
The flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat and lungs, resulting in mild to severe illness and at times can lead to death. Everyone six months of age and older should get a flu vaccine every season. This recommendation has been in place since Feb. 24, 2010, when the CDC's Advisory Committee on Immunization Practices (ACIP) voted for "universal" flu vaccination in the U.S. to expand protection against the flu to more people.
