2017-2018 Influenza Season
Nationally, the flu season peaked in early February with influenza A(H3) viruses being the predominant strains reported for the overall season. However, beginning in March influenza B strains were reported more commonly than A viruses. It is not unusual for there to be a second, lower wave of influenza activity later in the season. At the local level, the Southern Nevada Health District’s season mirrored national activity with cases beginning to decline shortly after the first of the year and more influenza B viruses being reported later in the season.
Influenza can occur throughout the year, and surveillance for flu occurs when activity is typically at its peak between October and May. The Health District follows the guidelines of the Centers for Disease Control and Prevention (CDC), tracking total case counts, deaths, and strains of circulating viruses. Each season, the Health District provides information to health care providers, community partners, and the public to educate them on the importance of flu vaccine as well as the best means of protection from the flu virus. The Health District also provides information on influenza antiviral medications as a second line of defense to treat flu illness and additional educational information and health tips related to flu season.
Because education and outreach are integral to the Health District’s efforts to provide timely information, updated flu statistics are released each week and posted on the agency’s website at Influenza Surveillance. The information provided includes the number of confirmed cases in Clark County, hospitalizations, and deaths for each week of the flu season. The Health District also posts an Influenza Surveillance Snapshot each week with a breakdown of influenza reports by virus strain, the weekly percentage of emergency room visits for Influenza-Like Illness (ILI), and additional charts and information useful to analyzing the season, examining seasonal trends, and providing information to CDC.
In keeping with CDC guidelines, Health District staff in the Office of Epidemiology and Disease Surveillance collaborated with its counterparts in the Vital Records program and the Nevada Department of Public and Behavioral Health to review and update outcome data for previously reported cases of influenza. As the season slowed, staff members were able to update outcome data of previously reported cases. This review did not add to the total influenza case count reported by the Health District but added to the verified death count. This process reflects the fluid nature of disease reporting, the arduous work it is, and the ongoing effort staff takes to make sure they are providing accurate data to health care partners, the media, and the public.
The effort to track flu and other reportable disease statistics is an ongoing program initiative. Providers who track reports and statistics on a regular basis know that data can be dynamic as new cases are identified throughout the year or season. Data may be updated if reporting lags and cases come in after a reporting period, if case definitions are updated, or as with flu, outcomes change from the time of an initial diagnosis.
This flu season provided a number of challenges to health care providers and public health professionals. Widespread coverage related to vaccine effectiveness also had many people questioning the need to get the vaccine this year, and health care professionals played a key role in providing accurate information, dispelling myths, and encouraging everyone who can be vaccinated to get a flu shot.
Interim influenza vaccine effectiveness for this season was published by the CDC in February and is estimated at 36 percent overall. Effectiveness is estimated at 25 percent against H3N2, 67 percent against H1N1, and 42 percent against influenza B viruses. This same study found that vaccine effectiveness against H3N2 among children 6 months to 8 years old was 51 percent. This year, the important message to provide to patients was that while vaccine effectiveness is lower, it is still the best protection against the virus.
Health care professionals can continue to work with public health to improve the approach to flu season. This includes timely reporting of flu cases and outcomes to ensure accurate data, appropriate use of antiviral medications for someone who is at high risk of complications from the flu or who is very sick, and advocating for production of a more effective “universal” flu vaccine.
More information on the current flu season visit the CDC website at www.cdc.gov/flu/.