Influenza Activity Slightly Increased Since Late August

Flu activity is typically low worldwide, but slightly increased in the US. Vaccination is recommended and antiviral treatment for patients at high risk.

Worldwide influenza rates were typical for the season between May 22 – September 10, 2016 and US rates were low overall. Since late August, however, US laboratories have been reporting that positive tests for flu have slightly increased, according to the Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report.1 In addition, influenza A (H3N2) has been causing a small number of local outbreaks.

Alicia Budd, MPH, of the Influenza Division at the National Center for Immunization and Respiratory Diseases at the CDC and colleagues report that there have been influenza A (H1N1)pdm09, influenza A (H3N2), and influenza B viruses identified during this period. In addition, the following variants were identified: influenza A (H1N2) and (H1N2v) viruses (1 in Minnesota and 1 in Wisconsin), and 18 influenza A (H3N2) and (H3N2v) viruses (12 from Michigan and 6 from Ohio).

“The majority of the influenza viruses collected from the United States and other countries during that time have been characterized antigenically or genetically or both as being similar to the reference viruses representing vaccine components recommended for the 2016-17 Northern Hemisphere vaccine,” the researchers wrote. The target strains in this year’s influenza vaccine are an A/California/7/2009 (H1N1)pdm09-like virus, an A/Hong Kong/4801/2014 (H3N2)-like virus, and a B/Brisbane/60/2008-like (B/Victoria lineage) virus for the trivalent vaccine and the additional influenza B virus (B/Phuket/3073/2013-like [B/Yamagata lineage]) for the quadrivalent vaccine.

Between May 22 – September 10, 5365 specimens were tested for influenza by labs in the US World Health Organization (WHO) Collaborating Laboratories System. Of these, 817 were positive. Influenza A was identified in 56.1% of cases (458), and 43.9% (351) were influenza B viruses. Researchers said there were more influenza B viruses reported during May and June, but that changed to more influenza A in July.

Of the influenza A cases identified, 84.2% (377) were influenza A (H3N2) viruses and 15.8% (71) were influenza A (H1N1)pdm09. Of the 249 Influenza B cases whose lineage was traced, Ms Budd and colleagues reported 69.1% (172) were B/Yamagata lineage and 77 30.9% (77) were B/Victoria lineage.

Researchers stressed that vaccination is “recommended for all persons aged ≥ 6 months, and can reduce the likelihood of becoming ill with influenza and transmitting the virus to others.” Getting the vaccine yearly offers the best protection, Ms Budd and colleagues said. Live attenuated intranasal vaccine (LAIV4) is not recommended for the 2016-2017 season due to “concerns about effectiveness.” Instead, the CDC recommends the inactivated influenza vaccine (IIV) or the recombinant influenza vaccine (RIV), researchers said.

Ms Budd and colleagues also said that if a patient has confirmed or suspected influenza virus, antiviral medication should be given as early as possible for patients who have, “severe, complicated, or progressive illness; who require hospitalization; or who are at high risk for influenza-related complications.” Researchers said physicians should be on the lookout for flu in those with flu-like symptoms despite low activity levels because of recent outbreak reports.

The recommendations by Ms Budd and colleagues in this report were reinforced by the National Foundation for Infectious Diseases (NFID) during a news conference held on September 29, 2016.2

Tom Frieden, MD, MPH, director of CDC, noted during the news conference that “if we could increase vaccination coverage in this country by just 5%, this would prevent about 800,000 illnesses and nearly 10,000 hospitalizations.”

Patricia N. Whitley-Williams, MD, NFID vice president and pediatric infectious disease physician at Rutgers-Robert Wood Johnson Medical School, in New Brunswick, New Jersey also spoke during the conference and stressed the importance of vaccinating pregnant women. She stated, “There is a reduced risk of flu illness in children born to women who were vaccinated during pregnancy compared to those infants born to women who were not vaccinated during pregnancy.” 

“On average, about 20,000 children under the age of 5 are hospitalized for flu-related complications each year in this country,” Dr Whitley-Williams said, adding that it is important parents get their children the influenza vaccine, especially since LAIV4 is not recommended for the 2016-17 influenza season.

Reporting on data from last year, Wilbur H. Chen, MD, associate professor of medicine and chief of the Adult Clinical Studies section at the Center for Vaccine Development at the University of Maryland in Baltimore, Maryland noted a slight drop in influenza vaccination rates among older adults.

Dr Chen noted during the news conference that in older adults, there are higher rates of infection, with more severe infections, and low vaccination response due to immunosenescence. “Seventy to 90% of influenza deaths that occur every year occur in the population of 65 years and older. Fifty to 70% of hospitalizations occur due to influenza in the 65 and over population,” stated Dr. Chen. So, in the older adult population, in addition to the influenza vaccination, pneumococcal vaccination is highly recommended. 

Older adults are at the highest risk for influenza. “Vaccination can prevent not just influenza illness, but also hospitalizations and death and complications.”  In addition, “the influenza vaccination also has been shown to decrease heart attacks, strokes, and other comorbid conditions,” concluded Dr. Chen.

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  1. Budd A, Blanton L, Kniss K, et al. Update: Influenza activity — United States and worldwide, May 22–September 10, 2016MMWR Morb Mortal Wkly Rep. 2016;65:1008-1014. doi: 10.15585/mmwr.mm6537a5.
  2. 2016 Influenza/Pneumococcal News Conference. Bethesda, MD: National Foundation for Infectious Diseases; September 29, 2016.