CDC: 2018-2019 Flu Season the Longest in a Decade

The 2018-2019 influenza season was moderately severe, with activity beginning to increase in November, peaking in mid-February, and returning to below baseline in mid-April. The 21-week season was the longest in 10 years, according to the CDC's recent Morbidity and Morality Weekly Report.

According to the report, influenza A viruses had significantly predominance, while influenza B virus had very little activity. There were 2 waves of influenza A during the season, influenza A (H1N1)pdm09 viruses from October 2018 to mid-February 2019 and influenza A(H3N2) viruses from February through May 2019.

Compared with the 2017-18 influenza season, rates of hospitalization this season were lower for adults, but similar for children. It was noted that the rates were most similar to those observed during 2014-15 and 2016-17 and well below those during 2017-18. Although influenza activity is currently below surveillance baselines, testing for seasonal influenza viruses and monitoring for novel influenza A virus infections should continue year-round.

The World Health Organization and National Respiratory and Enteric Virus Surveillance System laboratories contribute a virologic surveillance for influenza. During the 2018-2019 influenza season, clinical laboratories tested approximately 1.2 million specimens, and among those tested, 15.5% tested positive, including 95% for influenza A and 5.0% for influenza B.

Since the 2010—11 season, the CDC estimates influenza virus infection has caused 9.3 million–49 million symptomatic illnesses, 4.3 million–23 million medical visits, 140,000–960,000 hospitalizations, and 12,000–79,000 deaths during each influenza season. It is noted that preliminary estimates for the 2018-2019 season fall within these ranges.

Receiving a seasonal vaccine each year remains the best way to protect against seasonal influenza and its potentially severe consequences. Testing for seasonal influenza viruses and monitoring for emergence of antigenic drift variant viruses should continue year-round.

The study authors recommended that patients with confirmed or suspected influenza and who have severe, complicated, or progressive illness, those who require hospitalization, and those who are at high risk for influenza-associated complications to be treated as soon as possible with influenza antiviral medications. They noted that providers should not rely on less sensitive assay, such as rapid antigen detection influenza diagnostic tests to inform treatment decisions.

Four influenza antiviral drugs are approved by the FDA for treatment of acute uncomplicated influenza within 2 days of illness onset and are recommended for use in the United States during the 2018—19 season: oseltamivir, zanamivir, peramivir, and baloxavir.

Reference

Influenza Activity in the United States During the 2018—19 Season and Composition of the 2019–20 Influenza Vaccine. CDC website. Published June 21, 2019. https://www.cdc.gov/mmwr/volumes/68/wr/mm6824a3.htm?s_cid=mm6824a3_w. Accessed June 26, 2019.