Early influenza B activity causes some severe illness in Louisiana children
Click Here to Manage Email Alerts
The 2019-2020 influenza season in Louisiana arrived earlier than usual, with the majority of infections caused by influenza B — a strain that has not predominated in the United States in 27 years.
According to a recent report in MMWR, influenza activity in the state began before people typically start getting vaccinated. The symptoms and outcomes of influenza B-related illnesses in children in Louisiana have been similar to other influenza seasons, but some have been severe, researchers said.
Influenza B is more common among children than adults and can cause complications resulting in hospitalization or death. Influenza B also has predominated nationwide this season, with nearly 60% of influenza-positive samples testing positive for B virus.
“Influenza B/Victoria has not circulated widely for several years so children are quite susceptible,” Infectious Diseases in Children Editorial Board Member Kathryn M. Edwards, MD, an Infectious Diseases Society of America spokesperson and professor of pediatrics at Vanderbilt University Medical Center, told Healio. “Influenza B generally comes every year, but is usually not the predominant strain. I anticipate that it will be seen each year, but I do not anticipate that overall it will become more common than before.”
Melissa A. Rolfes, PhD, MPH, an epidemiologist in the CDC’s Influenza Division, and colleagues investigated 198 patients with influenza B from a single pediatric health care facility in New Orleans. The facility reported 1,268 lab-confirmed influenza B virus infections, 23 of which resulted in hospitalizations from July 31, 2019, to Nov. 21, 2019. During this period, a single pediatric influenza B-associated death was reported in Louisiana.
None of the patients had received a 2019-2020 seasonal influenza vaccine, and 81 of the 83 influenza B viruses sequenced from the patients belonged to the influenza B/Victoria genetic subclade. A total of 95% of the patients were aged younger than 18 years, serving as an indication of the threat influenza B poses to children.
Rolfes and colleagues stressed that all individuals aged 6 months or older should receive their annual influenza vaccination if they have not already.
“Nothing about influenza surprises me anymore,” Edwards said. “I have been trying to outsmart it for 40 years and must say that it is totally unpredictable.”
We spoke with Rolfes regarding the wider implications of influenza B’s increased prevalence, and what can be done to diminish the virus’ burden. – by Eamon Dreisbach
Q: What are the clinical implications of this report?
A: So far during the 2019-2020 season, influenza B/Victoria viruses have been the most common circulating influenza virus, mostly causing illness in young children and young adults. The B/Victoria viruses circulating throughout the U.S. are very similar to the viruses that caused the early and large influenza outbreak in Louisiana that we reported on in the MMWR.
When we looked at the clinical illnesses from the outbreak in Louisiana, we found that most illnesses were typical of influenza — respiratory illnesses that were primarily uncomplicated. However, hospitalizations, ICU admissions and a pediatric death due to influenza B were reported during the outbreak period, which serves as a reminder that influenza virus infections, including those due to influenza B, can be severe. Influenza antiviral treatment can reduce the duration of symptoms and possibly reduce the risk of severe complications, so it was great to see that in Louisiana about 70% of outpatients and more than 90% of the hospital admissions during the outbreak period were prescribed influenza antivirals.
The rest of the U.S. is also seeing elevated influenza activity right now and will be for many weeks. Influenza B continues to be the most common virus among children, but other influenza viruses are also circulating, such as influenza A and H1N1pdm09. With many more weeks, or months, of activity left for the 2019-2020 season, it’s not too late to get the influenza vaccine. Clinicians should continue to recommend the influenza vaccine for all people aged 6 months and older, which will help protect against influenza B/Victoria viruses but also against influenza A viruses.
Q: Are there factors specific to Louisiana that may account for the high incidence of influenza B across the state?
A: In general, we don’t know the reasons for why one influenza virus vs. another causes outbreaks or predominates during a season. In the Louisiana outbreak, there were likely multiple factors that created the opportunity for an outbreak. Influenza B/Victoria viruses have not circulated widely in the U.S. for several years, which could mean that the level of population immunity to influenza B/Victoria viruses was relatively low and allowed the viruses to infect more people. B/Victoria viruses have also recently undergone genetic changes, which could help the viruses evade pre-existing immunity. Additionally, schools in Louisiana also went back into session in early August, which may have created the environment for widespread transmission of influenza, particularly among school-aged children.
Q: Based on these data, do you foresee an uptick nationally in influenza B in the coming years?
A: It is challenging to predict which influenza viruses will predominate in any given season until the season is well underway. We may continue to see B/Victoria activity for several seasons, but we may also see that its predominance declines in the coming seasons. Both are possible, and it’s not simple to predict.
Q: What is the take-home message for clinicians?
A: What we saw in Louisiana is that severe complications from influenza B/Victoria virus infection can occur, and clinicians should remain vigilant about these serious complications. Influenza antiviral treatment can help reduce the duration of symptoms and may prevent serious complications. Thus, antivirals should be given to all patients hospitalized with suspected or confirmed influenza and to outpatients who are at high risk of influenza-associated complications, including those aged younger than 2 years or those with underlying medical conditions.
Q: How do these results compare with previous studies?
A: An analysis of data from patients hospitalized with influenza from the 2010-2011 season in the U.S. found that influenza B virus infection can cause severe complications, such as pneumonia and bacterial coinfection.
Q: Were there results from this study that surprised you?
A: There were a couple of surprising findings from the investigation of the outbreak of influenza B/Victoria viruses in Louisiana. First, the amount of illness that influenza caused was really staggering. At the height of the outbreak in mid-November, Louisiana was reporting high numbers of outpatient visits due to influenza-like-illness and at levels that were nearly record-breaking.
Secondly, all of this activity was early for the influenza season, too, occurring just as influenza vaccination campaigns were getting underway. From the individuals we investigated, none were vaccinated for the 2019-2020 season, likely in part because influenza was circulating before the time when vaccination typically occurs.
Q: What limitations were there for this report, and how can they be addressed for future analysis?
A: The report is based on an outbreak investigation that was conducted in one part of the state of Louisiana. Although influenza activity in the state, at the time, was primarily concentrated to this outbreak, the findings of the outbreak may not be generalizable to influenza activity that was occurring elsewhere in Louisiana. The investigation was also focused on patients seen at a large health care facility, and so the epidemiology of the outbreak may not reflect the epidemiology of influenza outside of the facility’s catchment area.
Finally, the findings were based on a chart and record review conducted on a sample of the outpatients with influenza B virus infection and may not be generalizable to all patients with influenza at the facility.
References:
CDC. Weekly U.S. Influenza Surveillance Report. https://www.cdc.gov/flu/weekly/index.htm. Accessed November 26, 2019.
Owusu D, et al. MMWR. 2019;doi:10.15585/mmwr.mm6902e1.
Disclosures: Edwards reports serving as an advisor for Bio-Net and Merck and on data safety and monitoring boards for Moderna, Pfizer, Sanofi, Seqirus and X-4 Pharmaceuticals. Rolfes reports no relevant financial disclosures.