Influenza
Influenza is a topic covered in the Johns Hopkins ABX Guide.
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PATHOGENS
- Influenza A (seasonal, U.S.):
- 2018-2019, season longest in a decade > 20 weeks with two waves of influenza A (H1N1 pdm09 predominated early with H3N2 seen more in Feb-May).
- 2019-2020, preliminary CDC estimates in the U.S. included 29-56 million infections, 410,00-740,000 hospitalizations and 24,000-62,000 deaths.
- The season may have been worse than 2018-2019, with more pediatric deaths (at least 144). Both influenza A and B strains were dominant, with influenza B typically striking children and younger adults more than the elderly.
- 2020-2021, minimal influenza activity, likely secondary to mitigation efforts for the coronavirus pandemic.
- Circulating viruses did alter from the prior year: influenza A accounted for 61.4%, with influenza B at 38.6%.
- Most (52.5%) of influenza A viruses were H3N2, and the majority (60%) of influenza B viruses were of Victoria lineage.
- In the U.S., 5 cases of Influenza A H1N1v, this variant infection occurred in patients with swine exposures.
- Circulating viruses did alter from the prior year: influenza A accounted for 61.4%, with influenza B at 38.6%.
- 2021-2022, some increase in influenza activity but not nearly to levels seen before the COVID-19 pandemic.
- CDC estimates that influenza virus infection resulted in 8.0–13.0 million symptomatic illnesses, 3.7–6.1 million medical visits, 82,000–170,000 hospitalizations, and 5,000–14,000 deaths in the U.S.
- Influenza A: recently active strains
- H1n1 pdm09 has been active annually since 2009; 2018-2019 accounted for most of the early season.
- H3N2: seasonal influenza, predominant influenza A strain in 2017-2022 in the U.S, and reflected the bulk of isolates in the 2021-2022 season.
- Pandemic H1N1 remains active since the pandemic in 2009 and continues to be identified in seasonal influenza.
- Other: multiple avian influenza or other strains
- Influenza B (seasonal): typically becomes more common later in a seasonal influenza season.
- Minimal activity during the 2021-2022 season.
- Influenza A: recently active strains
- CDC estimates that influenza virus infection resulted in 8.0–13.0 million symptomatic illnesses, 3.7–6.1 million medical visits, 82,000–170,000 hospitalizations, and 5,000–14,000 deaths in the U.S.
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PATHOGENS
- Influenza A (seasonal, U.S.):
- 2018-2019, season longest in a decade > 20 weeks with two waves of influenza A (H1N1 pdm09 predominated early with H3N2 seen more in Feb-May).
- 2019-2020, preliminary CDC estimates in the U.S. included 29-56 million infections, 410,00-740,000 hospitalizations and 24,000-62,000 deaths.
- The season may have been worse than 2018-2019, with more pediatric deaths (at least 144). Both influenza A and B strains were dominant, with influenza B typically striking children and younger adults more than the elderly.
- 2020-2021, minimal influenza activity, likely secondary to mitigation efforts for the coronavirus pandemic.
- Circulating viruses did alter from the prior year: influenza A accounted for 61.4%, with influenza B at 38.6%.
- Most (52.5%) of influenza A viruses were H3N2, and the majority (60%) of influenza B viruses were of Victoria lineage.
- In the U.S., 5 cases of Influenza A H1N1v, this variant infection occurred in patients with swine exposures.
- Circulating viruses did alter from the prior year: influenza A accounted for 61.4%, with influenza B at 38.6%.
- 2021-2022, some increase in influenza activity but not nearly to levels seen before the COVID-19 pandemic.
- CDC estimates that influenza virus infection resulted in 8.0–13.0 million symptomatic illnesses, 3.7–6.1 million medical visits, 82,000–170,000 hospitalizations, and 5,000–14,000 deaths in the U.S.
- Influenza A: recently active strains
- H1n1 pdm09 has been active annually since 2009; 2018-2019 accounted for most of the early season.
- H3N2: seasonal influenza, predominant influenza A strain in 2017-2022 in the U.S, and reflected the bulk of isolates in the 2021-2022 season.
- Pandemic H1N1 remains active since the pandemic in 2009 and continues to be identified in seasonal influenza.
- Other: multiple avian influenza or other strains
- Influenza B (seasonal): typically becomes more common later in a seasonal influenza season.
- Minimal activity during the 2021-2022 season.
- Influenza A: recently active strains
- CDC estimates that influenza virus infection resulted in 8.0–13.0 million symptomatic illnesses, 3.7–6.1 million medical visits, 82,000–170,000 hospitalizations, and 5,000–14,000 deaths in the U.S.
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Last updated: September 7, 2022
Citation
Auwaerter, Paul G. "Influenza." Johns Hopkins ABX Guide, The Johns Hopkins University, 2022. Johns Hopkins Guides, www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540285/all/Influenza.
Auwaerter PG. Influenza. Johns Hopkins ABX Guide. The Johns Hopkins University; 2022. https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540285/all/Influenza. Accessed March 24, 2023.
Auwaerter, P. G. (2022). Influenza. In Johns Hopkins ABX Guide. The Johns Hopkins University. https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540285/all/Influenza
Auwaerter PG. Influenza [Internet]. In: Johns Hopkins ABX Guide. The Johns Hopkins University; 2022. [cited 2023 March 24]. Available from: https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540285/all/Influenza.
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