Abstract
BackgroundUnderstanding influenza seasonality is necessary for determining policies for influenza control.AimWe characterised transmissibility during seasonal influenza epidemics, including one influenza pandemic, in Spain during the 21th century by using the moving epidemic method (MEM) to calculate intensity levels and estimate differences across seasons and age groups.MethodsWe applied the MEM to Spanish Influenza Sentinel Surveillance System data from influenza seasons 2001/02 to 2017/18. A modified version of Goldstein’s proxy was used as an epidemiological-virological parameter. We calculated the average starting week and peak, the length of the epidemic period and the length from the starting week to the peak of the epidemic, by age group and according to seasonal virus circulation.ResultsIndividuals under 15 years of age presented higher transmissibility, especially in the 2009 influenza A(H1N1) pandemic. Seasons with dominance/co-dominance of influenza A(H3N2) virus presented high intensities in older adults. The 2004/05 influenza season showed the highest influenza-intensity level for all age groups. In 12 seasons, the epidemic started between week 50 and week 3. Epidemics started earlier in individuals under 15 years of age (−1.8 weeks; 95% confidence interval (CI):−2.8 to −0.7) than in those over 64 years when influenza B virus circulated as dominant/co-dominant. The average time from start to peak was 4.3 weeks (95% CI: 3.6–5.0) and the average epidemic length was 8.7 weeks (95% CI: 7.9–9.6).ConclusionsThese findings provide evidence for intensity differences across seasons and age groups, and can be used guide public health actions to diminish influenza-related morbidity and mortality.
Highlights
Influenza is an important cause of hospital admission and mortality during seasonal influenza epidemics, and as such, constitutes a major issue for public health, healthcare strategy and resource allocation
We focused on characterising the transmissibility during seasonal influenza epidemics, including the 2009 influenza A(H1N1) pandemic, in Spain for the 2001/02 to 2017/18 influenza seasons using the moving epidemic method (MEM) [5,11] and an epidemiological-virological parameter (Goldstein’s proxy), in order to calculate intensity thresholds and intensity levels of the influenza epidemics that have occurred in Spain during the 21st century
Applying our method as part of weekly influenza surveillance during subsequent influenza seasons and possible pandemics will allow for the assessment of when influenza activity will start in real-time
Summary
Influenza is an important cause of hospital admission and mortality during seasonal influenza epidemics, and as such, constitutes a major issue for public health, healthcare strategy and resource allocation. The impact of influenza on the health of the population depends on the epidemiology of the disease, population susceptibility by age and circulating viruses, as well as other contributing factors such as vaccine coverage, vaccine effectiveness, social mixing patterns, specific humidity and climate [2,3] For this reason, analysing the start of the epidemic period, as well as the severity of the influenza epidemics every season, is important in order to be able to alert health services and ameliorate the morbidity, mortality and economic costs associated with influenza. Transmissibility, the indicator we focus on in this study, indicates the ease with which a virus may spread person-to-person and is an important determinant of the number of people who will be affected This can be measured using influenza incidence data obtained through routine influenza surveillance systems. Conclusions: These findings provide evidence for intensity differences across seasons and age groups, and can be used guide public health actions to diminish influenza-related morbidity and mortality
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
