It’s Just the Beginning of the 2018-2019 Influenza Season
Mary Anne Jackson, MD | Interim Dean - UMKC School of Medicine | Medical Editor, The Link Newsletter
Current surveillance data from the CDC regarding influenza activity allows us to make several predictions about the 2018-2019 influenza season.
- This is just the beginning. Anticipate that influenza activity will peak in late January or more likely in February. Generally, we see influenza-like activity increase ahead of hospitalizations, and at this point, I think we are seeing the upward trend in hospitalizations in children here in Kansas City. As we enter 2019, 10 regions across the U.S. reported Influenza Like Illness (ILI) visits above the national baseline, with more than one-half of all states reporting widespread influenza activity; this includes both Kansas and Missouri.
- Influenza A viruses are predominant and 90% are H1N1pdm09 subtypes; there are some A/H3N2 disease and B strains also identified. Annually, co-circulation of more than one influenza virus is typical and influenza B strains tend to emerge and peak later during each season. Consistent with data from prior seasons, where the increased toll of A/H1N1 disease in children is notable, the highest rates of hospitalization this year related to influenza have been among children younger than 5 years of age. The hospitalization rate for children younger than 5 years is 14.5 per 100,000 children. This compares to a rate of 5.4 per 100,000 individuals across all age groups. The Influenza Hospitalization Surveillance Network, which collects population-based data for laboratory-confirmed influenza-related hospitalizations confirms that 91.7% of hospitalized adults have an underlying medical condition (obesity, metabolic or cardiovascular disease), and 40.4% of hospitalized children have an underlying condition (asthma, obesity). Twenty-five percent of women between ages 15-44 years of age, who have been hospitalized this season so far, are pregnant, underscoring the importance of influenza vaccination in this population.
- There have been 13 pediatric deaths reported as of end of December 2018. All but one was related to the influenza A virus. While it is early in this year’s season, looking at data from three prior seasons, the gender breakdown of pediatric deaths tends to be approximately equal; early in this season, 80% of pediatric deaths are in girls, and over 50% are in the 5-17-year-age groups, with just over one-half having a high-risk underlying condition. Approximately 75-80% of children who die annually with influenza are unimmunized.
- There appears to be a good match between the vaccine strains in the inactivated vaccine products and the circulating viruses, so continue to immunize. The AAP in May recommended ahead of the season, the potential for an H1N1 year, and noted that while LAIV4 was being reintroduced with a new H1N1 (a/Slovenia) strain, there was no evidence to confirm vaccine effectiveness—hence, the preference for inactivated vaccine for children. New data just published, comparing the effectiveness of live attenuated influenza vaccine to inactivated influenza vaccine, using data from five studies, confirms the reduced effectiveness of LAIV4 against A/H1N1 strains for the 2013-2014 through 2015-2016 seasons, for children 2-17 years. (Pediatrics Chung JR, et al. Jan 7, 2019 http://pediatrics.aappublications.org/content/early/2019/01/03/peds.2018-2094). There is no information to date that evaluates the effectiveness of the new LAIV4 this year.
- Antivirals should be initiated as soon as possible for those with severe, complicated or progressive influenza, in those who require hospitalization, and for anyone who has a high-risk underlying condition. All tested viruses this year show susceptibility to oseltamivir, peramivir and zanamavir; data for baloxavir are not yet available.
- Expect to see influenza for at least another six to eight weeks minimum, and continue to recommend and give vaccine. Recognition of clinical influenza disease is essential to facilitate targeted testing and treatment. At this time of the season, expect cases of bacterial co-infection will increase. In a systematic review designed to identify the frequency of bacterial co-infection in influenza patients, 27 studies were examined, including seven focused on children, with two others that included adults and children. Streptococcus pneumoniae and Staphylococcus aureus, were the most commonly confirmed pathogens, followed by Group A streptococcus, Pseudomonas aeruginosa and Haemophilus influenzae (Klein EY, et al; Influenza and Other Respiratory Viruses 2016 Sep; 10(5):394-403). Simultaneous initiation of antiviral and antimicrobial therapy is recommended in those with influenza-associated pneumonia, and for other cases of suspected bacterial co-infection. Microbiological culture data should be utilized to optimize or de-escalate therapy as appropriate.