Data from the 2019-2020 season

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

Interim data from the 2020-2021 season

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.

2020-2021 Influenza Vaccine Components

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

Currently, there is very little influenza virus circulation in either the US (https://www.cdc.gov/flu/weekly/index.htm) or Europe (https://flunewseurope.org/).

Influenza Vaccine Recommendations

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

Highlights of current recommendations for influenza vaccination in pediatric SOT candidates and recipients:

• All persons ≥ 6 months of age who do not have a contraindication to immunization should receive the inactivated influenza vaccine (IIV); IIV should be given as early as possible during the influenza season, preferably before influenza is circulating in the local community.^10,12,13
• Children 6 months to 8 years of age who are receiving IIV for the first time or did not receipt two IIV doses previously, should receive a 2-dose series, with a 4-week interval between doses.
• There are few data to guide the optimal timing of IIV in children after SOT.
• Currently, IIV should be provided to SOT recipients beginning at 3-4 months after SOT, when receiving maintenance immunosuppression.
• Vaccination with IIV beginning as early as 1-2 months post-SOT may be considered if there is a community transmission of influenza. In this scenario, based on controlled data in adults, some experts may recommend a second dose of IIV to be given in the same season once the patient is receiving maintenance immunosuppression.^14-16
• Household contacts, caregivers, and health care workers providing care to children at higher risk for influenza complications (such as pediatric SOT) should also receive yearly influenza vaccination.
• Receipt of influenza vaccination does not protect against COVID-19; there are no associations with influenza vaccination and risk for COVID-19.¹⁷
• Influenza vaccination is safe and immunogenic in SOT recipients, but protection is not absolute. SOT recipients who develop influenza infection are at higher risk for influenza-associated complications and thus, are candidates for antiviral therapy, regardless of vaccination status or duration of symptoms.^10,18