Issue: March 2018
March 14, 2018
4 min read

Worst flu season in years hits pediatric patients hard

Issue: March 2018
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The worst influenza season in years has gripped much of the United States, leading to the highest rate of influenza-related hospitalizations in recent history, including for children, and underlining concerns about the seasonal vaccine.

“This season is a somber reminder of why flu is one of the world’s greatest public health challenges,” acting CDC Director Anne Schuchat, MD, said.

As of Feb. 23, 97 influenza-associated pediatric deaths were reported in the U.S., according to the CDC. The agency also reported 74.5 hospitalizations due to lab-confirmed influenza per 100,000 people in the U.S. If this rate is maintained through the end of the season, it would be the highest rate of hospitalizations since the CDC began using representative surveillance data from around a dozen sites in the country in 2010.

Thomas M. Kerkering

For comparison, the hospitalization rate in 2014-2015 — a recent benchmark for severe influenza seasons — was 43.5 per 100,000 people. The CDC estimated that influenza hospitalized 710,000 people that season, and officials said this season’s total could exceed that amount.

Children between the ages of 0 and 4 years hospitalized at a rate of 52.6 per 100,000, the top rate among people under 50 years of age.

“In my area in southwest Virginia, the highest number [of influenza cases] is in the 0 to 20 years age group,” Thomas M. Kerkering, MD, FACP, FIDSA, professor of medicine and chief of the division of infectious diseases at the Virginia Tech Carilion School of Medicine and medical director of infection control at the Carilion Clinic, told Infectious Diseases in Children.

“The only reason I can think this may be is that they have never encountered any of the antigens that some older people may have. Even though we are seeing quite a bit of infection in the older population, a little more than half of the infections are in children younger than 20 years,” he continued. “This just tells me that they do not have any immunity to the circulating viruses.”

H3N2, a vaccine-dodging influenza A strain known for causing relatively severe illness, has been the predominant strain all season. Adults aged 65 years and older have been the hardest hit population, followed by adults aged between 50 and 64 years and children aged younger than 5 years, according to Daniel B. Jernigan, MD, MPH, director of the CDC’s Influenza Division.

According to the CDC, adult mortality due to pneumonia or influenza — based on death certificates — was 9.5% during the week of Feb. 3, closing in on recent mortality peaks of 11.1% and 10.8% seen in the 2012-2013 and 2014-2015 seasons, respectively.


“This season is turning out to be a particularly challenging one,” Jernigan said. “It has been compounded by lots of flu occurring nationwide simultaneously over several weeks. This is an unusual pattern in the U.S.”

Anne Schuchat

Although both children and adults can experience severe complications from influenza, some children are at greater risk of developing intense illness and mortality than others.

“Some of the underlying issues related to more severe infection and flu-related death in children include concomitant respiratory syncytial virus or concomitant severe streptococcus infections,” Kerkering said. “Issues are also seen in children who have severe asthma. The influenza can trigger status asthmaticus, which is very difficult to treat, and children do not always survive that.”

According to Kerkering, these risk factors differ from those that adults may experience, which include chronic lung and heart disease.

The CDC reported the rate of outpatient visits attributed to influenza-like illness reached as high as 7.7%, matching the peak of the 2009 pandemic. It has dropped to 6.4 % in the week ending Feb. 17, a sign that the season may have peaked.

Kerkering mentioned that although wearing masks in an outpatient setting may assist in prevention efforts, it may be impractical for young pediatric patients and suggests alternative prevention methods.

“Most pediatricians know what to do. If they can set up a separate waiting room, they should do so for those that are coughing and those that are not.”

Additional complications this influenza season arose with spot shortages of Tamiflu in some states, including California. Furthermore, a shortage of intravenous saline was observed in January, with FDA Commissioner Scott Gottlieb, MD, stating in an update that hospitals and other health care organizations should contact the FDA if products have not been received. He also urges these organizations to follow clinical guidance provided by the American Society of Health-system Pharmacists and the University of Utah on managing these products during shortages.

Daniel B. Jernigan

For parents who are concerned about the severity of disease caused by H3N2, Kerkering suggested that although rates of infection are high, the amount of severe disease does not constitute removing children from school or extracurricular activities.

“You cannot keep children out of all activities. If we were seeing a lot of really serious disease, health departments would step in and close schools for a little while. I do not think that is happening in many places,” he said. “As a parent, I would tell children to frequently wash their hands because the influenza virus can get on objects. They touch them, and people frequently touch and scratch their faces.”


Jernigan said there was no laboratory evidence that circulating H3N2 viruses drifted significantly this season, but H3N2 viruses prepared using egg-based vaccine manufacturing methods already have adaptations that make them less similar to circulating viruses.

The CDC published estimates in mid-February showing that this season’s vaccine has been only 36% effective overall in the U.S., with only a 25% effectiveness against H3N2. The results were similar to estimates from other countries, including Australia and Canada.

“This is consistent with our concerns that the H3N2 influenza vaccine effectiveness is lower than against other types and that in recent years it’s been challenging to even get H3N2 protection,” Schuchat said.

However, the CDC continues to recommend patients get the vaccine.

“I would still encourage influenza vaccination,” Kerkering said. “Even though it might not be as effective as it was in years past, it may give children some exposure to the antigens that they may encounter. Some of the deaths in the pediatric and adolescent age groups are just simply due to an overwhelming immune response. It is not actually the virus itself; it was their own body’s weapons against it. If people are vaccinated, their bodies would be used to seeing these antigens and there may not be quite an onslaught of weaponry that is used against it.” – by Gerard Gallagher and Katherine Bortz

Disclosures: Jernigan, Kerkering and Schuchat report no financial disclosures.