How severe was the 2016-17 flu season? 7 key points

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Here are seven key points on the most recent flu season, which ran Oct. 2, 2016 through May 20, according to the CDC.

The points come from the CDC's June 30 Morbidity and Mortality Weekly Report.

1. Peak season. Flu activity picked up in December and peaked nationally in February, according to the CDC. This is an earlier peak than the 2015-16 season, which reached its height in terms of outpatient flu visits the week of March 6.

2. Outpatient flu visits. Outpatient visits for influenza-like illness remained at or above the baseline of 2.2 percent for 17 consecutive weeks. The peak occurred the week ending Feb. 11, when 5.1 percent of outpatient visits were due to influenza-like illness.

In the 2015-16 season, the highest peak for outpatient flu-like visits was 6.1 percent, and it remained at or above baseline for 13 consecutive weeks.

3. Flu hospitalizations. By the end of the season, the cumulative flu hospitalization rate for all age groups was 65 per 100,000 people. People 65 years old and older were the hardest hit — they accounted for about 60 percent of reported flu-associated hospitalizations.

This means more people were hospitalized for flu in the 2016-17 season than the prior season, when the flu hospitalization rate was 31.4 per 100,000.

4. Dominant flu strain. This season, H3N2 — which is usually associated with higher rates of hospitalizations and more deaths — was the dominant strain, similar to the 2014-15 season. However, H1N1 and influenza B strains were also reported this season.

5. New flu strains. Three people were infected with novel influenza A viruses during the most recent flu season:

  • An H1N2 variant was reported by Iowa public health officials during the week ending Nov. 19. The patient fully recovered without a trip to the hospital.
  • A person in New York was infected with a North American line of H7N2 virus during the week ending Dec. 24. This is the first bird flu virus identified in a human in the U.S. since 2003, and the first time such an infection was linked to exposure to a sick cat. The patient recovered without being hospitalized.
  • A third person was infected with an H3N2 variant virus. The person had been in contact with pigs before falling ill and fully recovered.

6. Vaccine efficacy. The 2016-17 flu vaccine reduced the risk for flu-associated medical visits by 42 percent.

That vaccine was slightly less effective than the 2015-16 vaccine (47 percent), but more effective than the 2014-15 vaccine (19 percent).

7. Effect on children. As of June 9, 98 children died from flu-related deaths in the 2016-17 season. This falls in the normal range of the number of pediatric flu deaths per season, according to the CDC, which is 37 to 171.


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