The IPTA ID committee (IDCARE) wishes to provide a brief influenza update in preparation for the upcoming 2020-2021 season in the Northern Hemisphere.
The epidemiology of the 2019-2020 influenza season was variable but in general, influenza activity ranged from moderate to very high across the globe.1 In the United States (US), the 2019-2020 influenza season was characterized by increased severity in children 0-4 years and adults 18-49 years of age when compared with the 2017-2018 high severity season; in total, at least 434 pediatric deaths were estimated to be associated with influenza during the 2019-2020 season.2,3
Preliminary/interim estimates of 2019-2020 influenza vaccine effectiveness (VE) from both Europe and the US are similar to prior seasons. Overall VE point estimates in Europe ranged between 29-61% (Europe) with VE in children <17 years ranging from 37-95% depending on the setting and the region.4 In the US, overall VE was 45% (95% CI 36-53%) and VE for pediatric patients (6 months-17 years) was 55% (95% CI 42-65%).5
Recent data suggest that interventions aimed against SARS-CoV-2 transmission (wearing a mask, physical distancing, handwashing) in conjunction with influenza vaccination, could substantially reduce the incidence and impact of influenza on the 2020-2021 season in the Northern Hemisphere.6 With the onset of widespread community transmission of SARS-CoV-2 and implementation of transmission mitigation efforts worldwide at the beginning of 2020, a marked decrease in influenza circulation was noted at the end of the 2019-2020 Northern Hemisphere influenza season.6 Moreover, influenza activity from June to August 2020 in the Southern Hemisphere remained very low.6 Given concerns for likely co-circulation of seasonal influenza and SARS-CoV-2 and known morbidity attributable to influenza among SOT recipients7, caution should be used and preventative strategies optimized by SOT candidates, recipients, their families and healthcare providers. Influenza vaccination remains a critical intervention to prevent influenza infection in pediatric SOT recipients.
As in prior seasons, quadrivalent vaccines contain one influenza A H1N1 2009 pandemic-like virus, one influenza A H3N2 virus, and two influenza B viruses (one from the Yamagata lineage and one from the Victoria lineage). Trivalent vaccines contain one of the influenza B virus strains (from the Victoria lineage). World Health Organization (WHO) recommendations for the 2020-2021 Northern Hemisphere influenza season updated all components except for the Yamagata lineage influenza B component.8 For the 2021 Southern Hemisphere influenza season, components are similar to those seen in the 2020-2021 northern hemisphere season with the exception of the influenza A H1N1 pandemic 2009-like virus.9
No major changes to influenza vaccination recommendations for children were made in the US for this season.10 European recommendations remain similar to prior years with some country-specific variability in influenza vaccine guidance.11