Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasons
Background: Annual seasonal influenza infection is unpredictable, and varies from season to season. Australia experienced a severe season in 2017, followed by a mild season in 2018. In 2019, it featured unusually high inter-seasonal activity followed by a severe H3N2 season, proclaimed by the medi...
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| Format: | Article |
| Language: | English |
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University of New South Wales
2019-11-01
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| Series: | Global Biosecurity |
| Subjects: | |
| Online Access: | https://jglobalbiosecurity.com/articles/47 |
| _version_ | 1818530974424629248 |
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| author | Aye Moa Mallory Trent Rob Menzies |
| author_facet | Aye Moa Mallory Trent Rob Menzies |
| author_sort | Aye Moa |
| collection | DOAJ |
| description | Background: Annual seasonal influenza infection is unpredictable, and varies from season to season. Australia experienced a severe season in 2017, followed by a mild season in 2018. In 2019, it featured unusually high inter-seasonal activity followed by a severe H3N2 season, proclaimed by the media as “the worst ever”. Following a severe season in 2017, enhanced vaccines were introduced in 2018 for people aged >65 years. Aim: To compare the seasonal severity of the 2017 and 2019 influenza season. Methods: Data were collated from the National Notifiable Diseases Surveillance System (NNDSS) report. Epidemiological trends of seasonal influenza infection were compared between the two years 2017 and 2019. Reported hospitalisations, ICU admissions and deaths were obtained from published sources and compared. Results: A(H3N2) dominated in both years. There was an early start to influenza circulation in 2019 with an unusually high number of cases seen during summer. There was no significant difference in the number of influenza hospitalisations or deaths reported in 2019 and 2017, but the proportion of hospitalisations that were admitted to ICU was significantly lower in 2019 (6.4% vs 8.9%, p<0.001). In both years, while large numbers of cases were reported, the severity of those cases was summarised as moderate. In 2019, 1108 influenza diagnoses per 100,000 population were notified to NNDSS up to October nationally, compared to 1021 per 100,000 for the same time period in 2017. There was variation in influenza activity by state in 2019, with Western Australia recording the highest activity and increased incidence compared to 2017. Most other states did not differ between 2019 and 2017. The 2017 epidemic affected the extremes of age more severely, as did 2019, but there was high activity in the young adult age group in 2019. Available data on the reported number of tests conducted in New South Wales and Western Australia were higher in 2019 than 2017. Vaccine effectiveness (VE) was reported initially as 40-60% for 2019 vs 33% (17-46%) in 2017. Conclusion: Both 2017 and 2019 were H3N2 seasons with large numbers of infections. Higher numbers of notifications to NNDSS were observed in 2019, probably due to an unusually high level of summer activity and increased testing. Clinical severity was estimated as similar to or less in 2019 compared to 2017. Estimated VE was higher in 2019 compared to 2017, and suggests a benefit of enhanced vaccines. |
| first_indexed | 2024-12-11T17:26:28Z |
| format | Article |
| id | doaj.art-9691d15b57854237a9ddcc5426bb37f4 |
| institution | Directory Open Access Journal |
| issn | 2652-0036 |
| language | English |
| last_indexed | 2024-12-11T17:26:28Z |
| publishDate | 2019-11-01 |
| publisher | University of New South Wales |
| record_format | Article |
| series | Global Biosecurity |
| spelling | doaj.art-9691d15b57854237a9ddcc5426bb37f42022-12-22T00:56:58ZengUniversity of New South WalesGlobal Biosecurity2652-00362019-11-011310.31646/gbio.4740Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasonsAye Moa0Mallory Trent1Rob Menzies2Biosecurity Program, Kirby Institute, University of New South WalesBiosecurity Program, Kirby Institute, University of New South WalesBiosecurity Program, Kirby Institute, University of New South WalesBackground: Annual seasonal influenza infection is unpredictable, and varies from season to season. Australia experienced a severe season in 2017, followed by a mild season in 2018. In 2019, it featured unusually high inter-seasonal activity followed by a severe H3N2 season, proclaimed by the media as “the worst ever”. Following a severe season in 2017, enhanced vaccines were introduced in 2018 for people aged >65 years. Aim: To compare the seasonal severity of the 2017 and 2019 influenza season. Methods: Data were collated from the National Notifiable Diseases Surveillance System (NNDSS) report. Epidemiological trends of seasonal influenza infection were compared between the two years 2017 and 2019. Reported hospitalisations, ICU admissions and deaths were obtained from published sources and compared. Results: A(H3N2) dominated in both years. There was an early start to influenza circulation in 2019 with an unusually high number of cases seen during summer. There was no significant difference in the number of influenza hospitalisations or deaths reported in 2019 and 2017, but the proportion of hospitalisations that were admitted to ICU was significantly lower in 2019 (6.4% vs 8.9%, p<0.001). In both years, while large numbers of cases were reported, the severity of those cases was summarised as moderate. In 2019, 1108 influenza diagnoses per 100,000 population were notified to NNDSS up to October nationally, compared to 1021 per 100,000 for the same time period in 2017. There was variation in influenza activity by state in 2019, with Western Australia recording the highest activity and increased incidence compared to 2017. Most other states did not differ between 2019 and 2017. The 2017 epidemic affected the extremes of age more severely, as did 2019, but there was high activity in the young adult age group in 2019. Available data on the reported number of tests conducted in New South Wales and Western Australia were higher in 2019 than 2017. Vaccine effectiveness (VE) was reported initially as 40-60% for 2019 vs 33% (17-46%) in 2017. Conclusion: Both 2017 and 2019 were H3N2 seasons with large numbers of infections. Higher numbers of notifications to NNDSS were observed in 2019, probably due to an unusually high level of summer activity and increased testing. Clinical severity was estimated as similar to or less in 2019 compared to 2017. Estimated VE was higher in 2019 compared to 2017, and suggests a benefit of enhanced vaccines.https://jglobalbiosecurity.com/articles/47influenza, influenza virus, notifications, season, h3n2 |
| spellingShingle | Aye Moa Mallory Trent Rob Menzies Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasons Global Biosecurity influenza, influenza virus, notifications, season, h3n2 |
| title | Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasons |
| title_full | Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasons |
| title_fullStr | Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasons |
| title_full_unstemmed | Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasons |
| title_short | Severity of the 2019 influenza season in Australia- a comparison between 2017 and 2019 H3N2 influenza seasons |
| title_sort | severity of the 2019 influenza season in australia a comparison between 2017 and 2019 h3n2 influenza seasons |
| topic | influenza, influenza virus, notifications, season, h3n2 |
| url | https://jglobalbiosecurity.com/articles/47 |
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