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Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1
BACKGROUND: Two subtypes of influenza A currently circulate in humans: seasonal H3N2 (sH3N2, emerged in 1968) and pandemic H1N1 (pH1N1, emerged in 2009). While the epidemiological characteristics of the initial wave of pH1N1 have been studied in detail, less is known about its infection dynamics dur...
Autores principales: | , , , , , , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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BioMed Central
2017
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5425986/ https://www.ncbi.nlm.nih.gov/pubmed/28494805 http://dx.doi.org/10.1186/s12879-017-2432-7 |
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author | Kwok, Kin On Riley, Steven Perera, Ranawaka A. P. M. Wei, Vivian W. I. Wu, Peng Wei, Lan Chu, Daniel K. W. Barr, Ian G. Malik Peiris, J. S. Cowling, Benjamin J. |
author_facet | Kwok, Kin On Riley, Steven Perera, Ranawaka A. P. M. Wei, Vivian W. I. Wu, Peng Wei, Lan Chu, Daniel K. W. Barr, Ian G. Malik Peiris, J. S. Cowling, Benjamin J. |
author_sort | Kwok, Kin On |
collection | PubMed |
description | BACKGROUND: Two subtypes of influenza A currently circulate in humans: seasonal H3N2 (sH3N2, emerged in 1968) and pandemic H1N1 (pH1N1, emerged in 2009). While the epidemiological characteristics of the initial wave of pH1N1 have been studied in detail, less is known about its infection dynamics during subsequent waves or its severity relative to sH3N2. Even prior to 2009, few data was available to estimate the risk of severe outcomes following infection with one circulating influenza strain relative to another. METHODS: We analyzed antibodies in quadruples of sera from individuals in Hong Kong collected between July 2009 and December 2011, a period that included three distinct influenza virus epidemics. We estimated infection incidence using these assay data and then estimated rates of severe outcomes per infection using population-wide clinical data. RESULTS: Cumulative incidence of infection was high among children in the first epidemic of pH1N1. There was a change towards the older age group in the age distribution of infections for pH1N1 from the first to the second epidemic, with the age distribution of the second epidemic of pH1N1 more similar to that of sH3N2. We found no serological evidence that individuals were infected in both waves of pH1N1. The risks of excess mortality conditional on infection were higher for sH3N2 than for pH1N1, with age-standardized risk ratios of 2.6 [95% CI: 1.8, 3.7] for all causes and 1.5 [95% CI: 1.0, 2.1] for respiratory causes throughout the study period. CONCLUSIONS: Overall increase in clinical incidence of pH1N1 and higher rates of severity in older adults in post pandemic waves were in line with an age-shift in infection towards the older age groups. The absence of repeated infection is good evidence that waning immunity did not cause the second wave. Despite circulating in humans since 1968, sH3N2 is substantially more severe per infection than the pH1N1 strain. Infection-based estimates of individual-level severity have a role in assessing emerging strains; updating seasonal vaccine components; and optimizing of vaccination programs. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12879-017-2432-7) contains supplementary material, which is available to authorized users. |
format | Online Article Text |
id | pubmed-5425986 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2017 |
publisher | BioMed Central |
record_format | MEDLINE/PubMed |
spelling | pubmed-54259862017-05-12 Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 Kwok, Kin On Riley, Steven Perera, Ranawaka A. P. M. Wei, Vivian W. I. Wu, Peng Wei, Lan Chu, Daniel K. W. Barr, Ian G. Malik Peiris, J. S. Cowling, Benjamin J. BMC Infect Dis Research Article BACKGROUND: Two subtypes of influenza A currently circulate in humans: seasonal H3N2 (sH3N2, emerged in 1968) and pandemic H1N1 (pH1N1, emerged in 2009). While the epidemiological characteristics of the initial wave of pH1N1 have been studied in detail, less is known about its infection dynamics during subsequent waves or its severity relative to sH3N2. Even prior to 2009, few data was available to estimate the risk of severe outcomes following infection with one circulating influenza strain relative to another. METHODS: We analyzed antibodies in quadruples of sera from individuals in Hong Kong collected between July 2009 and December 2011, a period that included three distinct influenza virus epidemics. We estimated infection incidence using these assay data and then estimated rates of severe outcomes per infection using population-wide clinical data. RESULTS: Cumulative incidence of infection was high among children in the first epidemic of pH1N1. There was a change towards the older age group in the age distribution of infections for pH1N1 from the first to the second epidemic, with the age distribution of the second epidemic of pH1N1 more similar to that of sH3N2. We found no serological evidence that individuals were infected in both waves of pH1N1. The risks of excess mortality conditional on infection were higher for sH3N2 than for pH1N1, with age-standardized risk ratios of 2.6 [95% CI: 1.8, 3.7] for all causes and 1.5 [95% CI: 1.0, 2.1] for respiratory causes throughout the study period. CONCLUSIONS: Overall increase in clinical incidence of pH1N1 and higher rates of severity in older adults in post pandemic waves were in line with an age-shift in infection towards the older age groups. The absence of repeated infection is good evidence that waning immunity did not cause the second wave. Despite circulating in humans since 1968, sH3N2 is substantially more severe per infection than the pH1N1 strain. Infection-based estimates of individual-level severity have a role in assessing emerging strains; updating seasonal vaccine components; and optimizing of vaccination programs. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12879-017-2432-7) contains supplementary material, which is available to authorized users. BioMed Central 2017-05-11 /pmc/articles/PMC5425986/ /pubmed/28494805 http://dx.doi.org/10.1186/s12879-017-2432-7 Text en © The Author(s). 2017 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. |
spellingShingle | Research Article Kwok, Kin On Riley, Steven Perera, Ranawaka A. P. M. Wei, Vivian W. I. Wu, Peng Wei, Lan Chu, Daniel K. W. Barr, Ian G. Malik Peiris, J. S. Cowling, Benjamin J. Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 |
title | Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 |
title_full | Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 |
title_fullStr | Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 |
title_full_unstemmed | Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 |
title_short | Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 |
title_sort | relative incidence and individual-level severity of seasonal influenza a h3n2 compared with 2009 pandemic h1n1 |
topic | Research Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5425986/ https://www.ncbi.nlm.nih.gov/pubmed/28494805 http://dx.doi.org/10.1186/s12879-017-2432-7 |
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