Practice Alert

Latest recommendations for the 2017-2018 flu season

This season’s vaccine has a new H1N1 component and any vaccine, except the live attenuated virus formulation, is suitable for pregnant women.


 

References

The Centers for Disease Control and Prevention (CDC) recently reported details of the 2016-2017 influenza season in Morbidity and Mortality Weekly Report1 and at the June meeting of the Advisory Committee on Immunization Practices. The CDC monitors influenza activity using several systems, and last flu season was shown to be moderately severe, starting in December in the Western United States, moving east, and peaking in February.

During the peak, 5.1% of outpatient visits were attributed to influenza-like illnesses, and 8.2% of reported deaths were due to pneumonia and influenza. For the whole influenza season, there were more than 18,000 confirmed influenza-related hospitalizations, with 60% of these occurring among those ≥65 years.1 Confirmed influenza-associated pediatric deaths totaled 98.1

The predominant influenza strain last year was type A (H3N2), accounting for about 76% of positive tests in public health laboratories (FIGURE).1 This was followed by influenza B (all lineages) at 22%, and influenza A (H1N1), accounting for only 2%. However, in early April, the predominant strain changed from A (H3N2) to influenza B. Importantly, all viruses tested last year were sensitive to oseltamivir, zanamivir, and peramivir. No antiviral resistance was detected to these neuraminidase inhibitors.

A look at the influenza strains in the 2016-2017 flu season image

Good news and bad news on vaccine effectiveness. The good news: Circulating viruses were a close match to those contained in the vaccine. The bad news: Vaccine effectiveness at preventing illness was estimated to be just 34% against A (H3N2) and 56% against influenza B viruses.1 There has been no analysis of the relative effectiveness of different vaccines and vaccine types.

The past 6 influenza seasons have revealed a pattern of lower vaccine effectiveness against A (H3N2) compared with effectiveness against A (H1N1) and influenza B viruses. While vaccine effectiveness is not optimal, routine universal use still prevents a great deal of mortality and morbidity. It’s estimated that in 2012-2013, vaccine effectiveness (comparable to that in 2016-2017) prevented 5.6 million illnesses, 2.7 million medical visits, 61,500 hospitalizations, and 1800 deaths.1

More good news: Vaccine safety studies are reassuring

The CDC monitors influenza vaccine safety by using several sources, including the Vaccine Adverse Event Reporting System and the Vaccine Safety Datalink.2 Studies were conducted using the Datalink network to assess incidences of anaphylaxis, Bell’s palsy, encephalitis, Guillain-Barré syndrome, seizures, and transverse myelitis. No increases in any of these conditions were found to be related to the influenza vaccine; nor were any new safety concerns detected.

Changes for the 2017-2018 influenza season

The composition of influenza vaccine products for the 2017-2018 season will differ slightly from last year’s formulation in the H1N1 component. Viral antigens to be included in the trivalent products are A/Michigan (H1N1), A/Hong Kong (H3N2), and B/Brisbane.3 Quadrivalent products will add B/Phuket to the other 3 antigens.3 A wide array of influenza vaccine products is available. Each one is described on the CDC Web site.4

Two minor changes in the recommendations were made at the June ACIP meeting.5 Afluria is approved by the FDA for use in children starting at age 5 years. ACIP had recommended that its use be reserved for children 9 years and older because previous influenza seasons had raised concerns about increased rates of febrile seizures in children younger than age 9. These concerns have been resolved, however, and the ACIP recommendations are now in concert with those of the FDA for this product.

Influenza immunization with an inactivated influenza vaccine product has been recommended for all pregnant women. Safety data are increasingly available for other product options as well, and ACIP now recommends vaccination in pregnancy with any age-appropriate product except for live attenuated influenza vaccine. 5

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