CDC: Second Wave Of "B-Strain" Influenza Has Begun, "More Severe For Younger Children"

Despite the flu season finally winding down and overall cases declining, the CDC reports that infections of the less common "Influenza B" strain are on the rise, surpassing "Influenza A" in their most recent weekly Influenza Surveillance Report. This season's strains are a mixture of the H3N2 and H1N1 "A" strains and the now-resurgent "B" strain, which can be particularly severe on young children. 

The March 23 release shows that cases of the B-strain comprised nearly 60% of new cases across the country - as reported during the week of March 17.

"We know that illness associated with influenza B can be just as severe as illness associated with influenza A," said CDC spokesperson Kristen Nordlund via CNN. "We also know that influenza B tends to be more severe for younger children."

This year there have been 26,694 hospitalizations for flu-related symptoms, nearly 80% of which have been Influenza A - however the late-season resurgence of Influenza B should be of particular concern to parents of younger children as well as caretakers. 

"We often see a wave of influenza B during seasons when influenza A H3N2 was the predominant virus earlier in the season. Unfortunately, we don't know what the influenza B wave will look like," said Norland, who adds that it's possible to get sick with multiple strains of the flu within the same season. 

133 children have died so far from flu-related illnesses during the 2017-2018 season. Among adults, 7.8% of deaths reported for the week were flu related - noting a two week delay in the data. The CDC had estimated a threshold of 7.4%.

Other notable trends via the CDC update: 

During week 11 (March 11-17, 2018), influenza activity decreased in the United States.

  • Viral Surveillance: Overall, influenza A(H3) viruses have predominated this season. However, in recent weeks the proportion of influenza A viruses has declined, and during week 11, influenza B viruses were more frequently reported than influenza A viruses. The percentage of respiratory specimens testing positive for influenza in clinical laboratories decreased.
  • Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was above the system-specific epidemic threshold in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
  • Influenza-associated Pediatric Deaths: Five influenza-associated pediatric deaths were reported.
  • Influenza-associated Hospitalizations: A cumulative rate of 93.5 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported.
  • Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 2.7%, which is above the national baseline of 2.2%. Nine of 10 regions reported ILI at or above region-specific baseline levels. Six states experienced high ILI activity; nine states experienced moderate ILI activity; New York City, Puerto Rico, the District of Columbia, and 17 states experienced low ILI activity; and 18 states experienced minimal ILI activity.
  • Geographic Spread of Influenza: The geographic spread of influenza in 17 states was reported as widespread; Guam, Puerto Rico and 26 states reported regional activity; the District of Columbia and five states reported local activity; and the U.S. Virgin Islands and two states reported sporadic activity.

To prevent the flu, the CDC recommends: 

1. Avoid close contact.

Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.

2. Stay home when you are sick.

If possible, stay home from work, school, and errands when you are sick. This will help prevent spreading your illness to others.

3. Cover your mouth and nose.

Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick.

4. Clean your hands.

Washing your hands often will help protect you from germs. If soap and water are not available, use an alcohol-based hand rub.

5. Avoid touching your eyes, nose or mouth.

Germs are often spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.

6. Practice other good health habits.

Clean and disinfect frequently touched surfaces at home, work or school, especially when someone is ill. Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food.