Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1
Abstract 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 dyna...
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| Format: | Article |
| Language: | English |
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BMC
2017-05-01
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| Series: | BMC Infectious Diseases |
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| Online Access: | http://link.springer.com/article/10.1186/s12879-017-2432-7 |
| _version_ | 1818190985449963520 |
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| author | Kin On Kwok Steven Riley Ranawaka A. P. M. Perera Vivian W. I. Wei Peng Wu Lan Wei Daniel K. W. Chu Ian G. Barr J. S. Malik Peiris Benjamin J. Cowling |
| author_facet | Kin On Kwok Steven Riley Ranawaka A. P. M. Perera Vivian W. I. Wei Peng Wu Lan Wei Daniel K. W. Chu Ian G. Barr J. S. Malik Peiris Benjamin J. Cowling |
| author_sort | Kin On Kwok |
| collection | DOAJ |
| description | Abstract 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. |
| first_indexed | 2024-12-12T00:07:25Z |
| format | Article |
| id | doaj.art-a44b12a5f4d14db196262b1001eca313 |
| institution | Directory Open Access Journal |
| issn | 1471-2334 |
| language | English |
| last_indexed | 2024-12-12T00:07:25Z |
| publishDate | 2017-05-01 |
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| series | BMC Infectious Diseases |
| spelling | doaj.art-a44b12a5f4d14db196262b1001eca3132022-12-22T00:45:05ZengBMCBMC Infectious Diseases1471-23342017-05-0117111210.1186/s12879-017-2432-7Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1Kin On Kwok0Steven Riley1Ranawaka A. P. M. Perera2Vivian W. I. Wei3Peng Wu4Lan Wei5Daniel K. W. Chu6Ian G. Barr7J. S. Malik Peiris8Benjamin J. Cowling9JC School of Public Health and Primary Care, Faculty of Medicine, The Chinese University of Hong KongMRC Centre for Outbreak Analysis and Modelling, Department for Infectious Disease Epidemiology, Imperial College LondonWHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong KongWHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong KongWHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong KongWHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong KongWHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong KongWHO Collaborating Centre for Reference and ResearchWHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong KongWHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong KongAbstract 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.http://link.springer.com/article/10.1186/s12879-017-2432-7InfluenzaSeroepidemiologySeverityCohortSevere outcomes |
| spellingShingle | Kin On Kwok Steven Riley Ranawaka A. P. M. Perera Vivian W. I. Wei Peng Wu Lan Wei Daniel K. W. Chu Ian G. Barr J. S. Malik Peiris Benjamin J. Cowling Relative incidence and individual-level severity of seasonal influenza A H3N2 compared with 2009 pandemic H1N1 BMC Infectious Diseases Influenza Seroepidemiology Severity Cohort Severe outcomes |
| 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 | Influenza Seroepidemiology Severity Cohort Severe outcomes |
| url | http://link.springer.com/article/10.1186/s12879-017-2432-7 |
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