Background Influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus are the most common viruses associated with acute lower respiratory infections in young children (<5 years) and older people (≥65 years). A global report of the monthly activity of these viruses is needed to inform public health strategies and programmes for their control. Methods In this systematic analysis, we compiled data from a systematic literature review of studies published between Jan 1, 2000, and Dec 31, 2017; online datasets; and unpublished research data. Studies were eligible for inclusion if they reported laboratory-confirmed incidence data of human infection of influenza virus, respiratory syncytial virus, parainfluenza virus, or metapneumovirus, or a combination of these, for at least 12 consecutive months (or 52 weeks equivalent); stable testing practice throughout all years reported; virus results among residents in well-defined geographical locations; and aggregated virus results at least on a monthly basis. Data were extracted through a threestage process, from which we calculated monthly annual average percentage (AAP) as the relative strength of virus activity. We defined duration of epidemics as the minimum number of months to account for 75% of annual positive samples, with each component month defined as an epidemic month. Furthermore, we modelled monthly AAP of influenza virus and respiratory syncytial virus using site-specific temperature and relative humidity for the prediction of local average epidemic months. We also predicted global epidemic months of influenza virus and respiratory syncytial virus on a 5° by 5° grid. The systematic review in this study is registered with PROSPERO, number CRD42018091628. Findings We initally identified 37 335 eligible studies. Of 21 065 studies remaining after exclusion of duplicates, 1081 full-text articles were assessed for eligibility, of which 185 were identified as eligible. We included 246 sites for influenza virus, 183 sites for respiratory syncytial virus, 83 sites for parainfluenza virus, and 65 sites for metapneumovirus. Influenza virus had clear seasonal epidemics in winter months in most temperate sites but timing of epidemics was more variable and less seasonal with decreasing distance from the equator. Unlike influenza virus, respiratory syncytial virus had clear seasonal epidemics in both temperate and tropical regions, starting in late summer months in the tropics of each hemisphere, reaching most temperate sites in winter months. In most temperate sites, influenza virus epidemics occurred later than respiratory syncytial virus (by 0•3 months [95% CI-0•3 to 0•9]) while no clear temporal order was observed in the tropics. Parainfluenza virus epidemics were found mostly in spring and early summer months in each hemisphere. Metapneumovirus epidemics occurred in late winter and spring in most temperate sites but the timing of epidemics was more diverse in the tropics. Influenza virus epidemics had shorter duration (3•8 months [3•6 to 4•0]) i...

Background Knowledge on age-specific hospitalizations associated with RSV infection is limited due to limited testing, especially in older children and adults in whom RSV infections are not expected to be severe. Burden estimates based on RSV coding of hospital admissions are known to underestimate the burden of RSV. We aimed to provide robust and reliable age-specific burden estimates of RSV-associated hospital admissions based on data on respiratory infections from national health registers and laboratory-confirmed cases of RSV. Methods We conducted multiseason regression analysis of weekly hospitalizations with respiratory infection and weekly laboratory-confirmed cases of RSV and influenza as covariates, based on national health registers and laboratory databases across 6 European countries. The burden of RSV-associated hospitalizations was estimated by age group, clinical diagnosis, and presence of underlying medical conditions. Results Across the 6 European countries, hospitalizations of children with respiratory infections were clearly associated with RSV, with associated proportions ranging from 28% to 60% in children younger than 3 months and we found substantial proportions of admissions to hospital with respiratory infections associated with RSV in children younger than 3 years. Associated proportions were highest among hospitalizations with ICD-10 codes of “bronchitis and bronchiolitis.” In all 6 countries, annual incidence of RSV-associated hospitalizations was &gt;40 per 1000 persons in the age group 0–2 months. In age group 1–2 years the incidence rate ranged from 1.3 to 10.5 hospitalizations per 1000. Adults older than 85 years had hospitalizations with respiratory infection associated to RSV in all 6 countries although incidence rates were low. Conclusions Our findings highlight the substantial proportion of RSV infections among hospital admissions across different ages and may help public health professionals and policy makers when planning prevention and control strategies. In addition, our findings provide valuable insights for health care professionals attending to both children and adults presenting with symptoms of viral respiratory infections.

Background The ongoing pandemic of Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 virus could recur as seasonal outbreaks, a circulating pattern observed among other pre-existing human seasonal coronaviruses (sCoV). However, little is known about seasonality of sCoV on a global scale. Methods We conducted a systematic review of data on seasonality of sCoV. We compared seasonality of sCoV with influenza virus and respiratory syncytial virus. We modelled monthly activity of sCoV using site-specific weather data. Results We included sCoV seasonality data in 40 sites from 21 countries. SCoV was prevalent in winter months in most temperate sites except for China while sCoV tended to be less seasonal in China and in tropical sites. In temperate sites excluding China, 53.1% of annual sCoV cases (Interquartile range, IQR: 34.6–61.9) occurred during influenza season and 49.6% (IQR: 30.2–60.2) of sCoV occurred during respiratory syncytial virus season. Low temperature combined with high relative humidity was associated with higher sCoV activity. Conclusions This is the first study that provides an overview of the global seasonality of sCoV. Our findings offer clues to the possible post-pandemic circulating season of SARS-CoV-2 and add to the knowledge pool necessary for post-pandemic preparedness for SARS-CoV-2.

Background Respiratory syncytial virus (RSV) is a leading cause of respiratory tract infection (RTI) in young children. Registries provide opportunities to explore RSV epidemiology and burden. Methods We explored routinely collected hospital data on RSV in children aged &lt; 5 years in 7 European countries. We compare RSV-associated admission rates, age, seasonality, and time trends between countries. Results We found similar age distributions of RSV-associated hospital admissions in each country, with the highest burden in children &lt; 1 years old and peak at age 1 month. Average annual rates of RTI admission were 41.3–112.0 per 1000 children aged &lt; 1 year and 8.6–22.3 per 1000 children aged &lt; 1 year. In children aged &lt; 5 years, 57%–72% of RTI admissions with specified causal pathogen were coded as RSV, with 62%–87% of pathogen-coded admissions in children &lt; 1 year coded as RSV. Conclusions Our results demonstrate the benefits and limitations of using linked routinely collected data to explore epidemiology and burden of RSV. Our future work will use these data to generate estimates of RSV burden using time-series modelling methodology, to inform policymaking and regulatory decisions regarding RSV immunization strategy and monitor the impact of future vaccines.

Non-pharmaceutical interventions (NPIs) were widely introduced to combat the COVID-19 pandemic. These interventions also likely led to substantially reduced activity of respiratory syncytial virus (RSV). From late 2020, some countries observed out-of-season RSV epidemics. Here, we analyzed the role of NPIs, population mobility, climate, and SARS-CoV-2 circulation in RSV rebound through a time-to-event analysis across 18 countries. Full (re)-opening of schools was associated with an increased risk for RSV rebound (HR = 23.29 [95% CI: 1.09–495.84]); every 5°C increase in temperature was associated with a decreased risk (HR = 0.63 [0.40–0.99]). There was an increasing trend in the risk for RSV rebound over time, highlighting the role of increased population susceptibility. No other factors were found statistically significant. Further analysis suggests increasing population susceptibility and full (re)-opening of schools could both override the counter-effect of high temperatures, which explains the out-of-season RSV epidemics during the COVID-19 pandemic.