Flu season occurs every year in the United States in the fall and the winter. The peak of flu season varies each year but generally occurs from late November through March. In preparation of the annual flu season, routine vaccination against seasonal influenza is recommended for all persons greater than or equal to 6 months of age. But why is there a scare around our annual influenza season this year?
According to weekly influenza activity reports from the Centers for Disease Control and Prevention (CDC), we have seen early widespread and elevated influenza activity this season:
- In the most recent data for the week ending in January 31, there was a decline in influenza-like illness related medical visits of 4.1%, but it remains above the national baseline of 2 % for the eleventh consecutive week.
- The proportion of deaths attributed to pneumonia and influenza (P&I) is an alarming rate of 8.5%, which is above the epidemic threshold of 7.2%.
It is a common misconception that if one has received an influenza vaccine, he or she will not get the common flu anytime soon. Realistically, the overall annual flu vaccine effectiveness estimate varies for each season; ranging from 10 to 60% effectiveness in preventing medical visits associated with seasonal influenza illness. While the seasonal influenza vaccine is designed to protect against the influenza viruses during flu season, this is not an exact science. Viruses are constantly changing and the influenza viruses are no exception. The influenza vaccine is updated each year based on research investigating which influenza viruses are spreading and making people sick. This worldwide effort involves more than 100 national influenza centers in more than 100 countries that conduct year-round surveillance for influenza. This process requires extensive testing of thousands of influenza virus samples from patients with suspected flu illness.
This season, influenza A (H3N2) viruses have been the predominate influenza virus strain based on reported cases and culture specimens. Influenza A (H3N2) is historically associated with higher overall and age-specific hospitalization rates and mortality in comparison to influenza A (H1N1) or influenza B viruses. Early influenza viral characterization data indicates that while 48% of the influenza A (H3N2) viruses were antigenically similar to the 2014 – 2015 influenza A vaccine component, 52% were antigenically different or “drifted” from the H3N2 vaccine virus. Due to the rise of drifted variants of influenza A (H3N2), this year’s flu vaccine is only 23% effective in preventing medical visits associated with seasonal influenza illness.
Antiviral treatment with oseltamivir (Tamiflu®), zanamivir (Relenza®) or peramivir (Rapivab®) is recommended to be administered as early as possible, ideally within 48 hours of symptom onset for any patients with suspected or confirmed influenza who are: hospitalized; have severe, complicated or progressive illness; or are at high risk for influenza complications.
While the manufacturers of the antiviral medications have stated that there is no national shortage of these agents, some isolated spot shortages have been observed. The CDC advises that it may be necessary for prescribers and/or patients to contact more than one pharmacy to locate supply and successfully fill an antiviral medication prescription.
Although our current vaccine may not be highly effective, it is the best tool available for prevention of influenza and is especially important for people at high risk for serious flu complications, and their close contacts. Flu vaccination can reduce the risk of more serious flu outcomes, like hospitalizations and deaths. In the meantime, proper hand hygiene and cough and sneeze etiquette can help decrease the spread of influenza. Most importantly, people who are sick should stay home from work or school to avoid exposing others to the virus.
Author: Yin Wong, PharmD