Explore This IssueACEP Now: Vol 33 – No 11 – November 2014
Have you enjoyed the lovely summer and fall? I hope so because as some people say, “winter is coming,” and with winter comes the return of influenza.
The 2014–2015 Flu Season
By the first week of September 2014, the yearly cycle of influenza had dropped to its nadir. Only 1 percent of all influenza tests were positive at participating laboratories surveyed by the Centers for Disease Control and Prevention (CDC). After peaking at 5,000 positive tests per biweekly period last Christmas, now there were fewer than 20. Since September, we’ve been witnessing a gradual increase in both positive tests and percentage of tests positive.1
The last two influenza seasons reached epidemic thresholds in the United States. The winters of both 2013 and 2014 experienced significant spikes in mortality associated with pneumonia and influenza, several standard deviations above the seasonal norm. Last season, at its peak, the vast majority of infections were influenza A viruses, and the predominant strain was the H1N1 subtype, the so-called “swine flu,” initially detected in 2009. This strain of influenza has been associated with increased case-fatality rates, particularly at the age-range extremes of greater than 65 years and less than 5. This strain is also associated with an excess incidence of the acute respiratory distress syndrome secondary to cytokine and chemokine release in otherwise healthy individuals outside the typical risk groups.
While the particular strains of circulating influenza are challenging to predict, this year’s influenza vaccines in the Northern Hemisphere consist of the following:
- Influenza A/California/7/2009 (H1N1)pdm09–like virus
- Influenza A/Texas/50/2012 (H3N2)–like virus
- Influenza B/Massachusetts/2/2012–like virus.
Approximately half of the doses manufactured for the 2014–2015 season will be tetravalent and include an additional B virus:
- Influenza B/Brisbane/60/2008–like virus
The only change from last year’s vaccine is an updated version of the H3N2 variant, replacing an influenza A/Victoria/361/2011–like virus. Vaccination group recommendations are unchanged from previous years, and health care workers are again universally encouraged to protect themselves and their patients through vaccination.
As with each influenza season, the CDC tracks the emergence of novel influenza A variants. The prevailing worrisome variant has been a highly pathogenic H5N1 strain known as “avian influenza.” At this time, only sporadic cases have been reported to the World Health Organization from the Middle East and Southeast Asia, and they have followed close contact with poultry. Another relatively lethal avian strain, H7N9, has been reported in sporadic cases throughout China and Malaysia. Lastly, a novel variant H3N2v avian strain containing genetic material from the H1N1 swine strain is being tracked. However, after peaking at 309 reported cases in 2012, only two cases of this crossover strain have been reported as of this writing. While it is too late to change the 2014–2015 vaccine components, emergence of any new pathogenic strains may change CDC recommendations for antiviral use.
Updates on Antiviral Use
The CDC has not altered its current recommendations for treatment of seasonal influenza.2 As is familiar to most clinicians, this includes the neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza), with recommendations to initiate therapy in high-risk groups within 48 hours of symptom onset. Patients hospitalized for respiratory illness and suspected or confirmed influenza should also be considered for antiviral therapy beyond 48 hours.