Epidemiology of influenza

doi:10.1016/j.vaccine.2008.07.066

Vaccine

Volume 26, Supplement 4, 12 September 2008, Pages D45-D48

https://doi.org/10.1016/j.vaccine.2008.07.066 Get rights and content

Abstract

The impact of influenza has been recognized for centuries. Its seasonality in temperate climates has allowed estimates of mortality and severe morbidity, such as hospitalization, to be made statistically, without identifying cases virologically. Most influenza related mortality occurs in older individuals and those with underlying conditions. In addition to those groups, influenza hospitalizations occur in younger children and pregnant women. Morbidity is more difficult to identify and laboratory confirmation is required for precise estimates to be made. Younger individuals experience the highest frequency of illnesses caused by all subtypes. This has resulted in suggested strategies for community control by vaccinating children.

Section snippets

Seasonality of influenza

The fact that, in the temperate zone, influenza is highly seasonal is a major reason that it has been possible to estimate the impact of influenza without identifying those infected using laboratory techniques. In the Northern Hemisphere, there may be viruses identified at other times of the year, but outbreaks rarely begin before late November. Generally, outbreaks dominated by A (H3N2) start earlier, with type B following and often closing the season [13], [14]. Especially in those years in

Effect of influenza type and subtype and of age

The two type A viruses (H3N2) and (H1N1) and type B viruses produce illnesses of relatively similar clinical characteristics. However, in older children and healthy adults, it is possible to demonstrate that A (H3N2) virus is associated with the most severe illnesses, A (H1N1) the mildest, and type B intermediate. This can be observed in differences in overall duration of uncomplicated illnesses in the general population [12]. In the elderly and in other at-risk populations, complications

Influenza impact: mortality and hospitalizations

The historic observations that, in influenza outbreaks, certain population groups were at increased risk of death were made at a time when the influenza virus had not been identified. Even when influenza viruses could be isolated, identification of the viral etiology of an event as rare as death was not feasible, especially with the techniques then available. Several epidemiologic methods have been developed to estimate the number of deaths associated with influenza, using laboratory data as a

Influenza morbidity and indirect protection

It is much more difficult to quantify influenza morbidity. While it is possible to identify typical influenza based on clinical characteristics during the influenza season, much influenza is milder and would not be recognized without laboratory confirmation. Such studies, which have been done in large enough populations and over several seasons, characteristics which allow generalizability have been found [38]. A generalization, based on a limited number of studies conducted long enough, is

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Influenza viruses share the same routes of transmission as coronaviruses [17], and indoor air ventilation is a suitable way to reduce the risk of infection too [18], as can be seen by comparing the spread of influenza before and after the implementation of the anti-contagion measures dictated by the COVID-19 pandemic [19]. The severity and size of influenza viruses vary from year to year [20] causing sick leave among students which has an economic impact with the related direct and indirect costs (medical visits, diagnostic investigations, hospital admissions, drugs, and parental absenteeism from work) [21]. Hence, promoting acceptable indoor air changes in school environments has proven to bring many advantages to students.
The recent pandemic due to SARS-CoV-2 has brought to light the need for strategies to mitigate contagion between human beings. Apart from hygiene measures and social distancing, air ventilation highly prevents airborne transmission within enclosed spaces. Among others, educational environments become critical in strategic planning to control the spread of pathogens and viruses amongst the population, mainly in cold conditions. In the event of a virus outbreak – such as COVID or influenza – many school classrooms still lack the means to guarantee secure and healthy environments.
The present review examines school contexts that implement air ventilation strategies to reduce the risk of contagion between students. The analysed articles present past experiences that use either natural or mechanical systems assessed through mathematical models, numerical models, or full-scale experiments. For naturally ventilated classrooms, the studies highlight the importance of the architectural design of educational spaces and propose strategies for aeration control such as CO₂-based control and risk-infection control. When it comes to implementing mechanical ventilation in classrooms, different systems with different airflow patterns are assessed based on their ability to remove airborne pathogens considering parameters like the age of air and the generation of airflow streamlines. Moreover, studies report that programmed mechanical ventilation systems can reduce risk-infection during pandemic events.
In addition to providing a systematic picture of scientific studies in the field, the findings of this review can be a valuable reference for school administrators and policymakers to implement the best strategies in their classroom settings towards reducing infection risks.
Respiratory viral infections
2019, Genomic and Precision Medicine: Infectious and Inflammatory Disease
Molecular analysis of respiratory viruses and the host response to both infection and vaccination have transformed our understanding of these ubiquitous pathogens. Polymerase chain reaction for the rapid and accurate diagnosis of viral infections has led to a better understanding of the epidemiology and impact of many common respiratory viruses and resulted in better patient care. Over the past decade a number of new respiratory viruses including human metapneumovirus and new coronaviruses have been discovered using molecular techniques such as random primer amplification, pan-viral array and next generation sequencing. Analysis of the host transcriptional response during respiratory viral infection using in-vitro, animal models and natural and experimental human challenge have furthered the understanding of the mechanisms and predictors of severe disease and may identify potential therapeutic targets to prevent and ameliorate illness.
Economic burden of seasonal influenza in the United States
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Citation Excerpt :
Seasonal influenza is a highly pathogenic viral infection. It occurs annually in the United States (U.S.) typically from late fall through early-mid spring [1,2]. Influenza infection is common in all age groups, with children infected most frequently.
Seasonal influenza is responsible for a large disease and economic burden. Despite the expanding recommendation of influenza vaccination, influenza has continued to be a major public health concern in the United States (U.S.). To evaluate influenza prevention strategies it is important that policy makers have current estimates of the economic burden of influenza.
To provide an updated estimate of the average annual economic burden of seasonal influenza in the U.S. population in the presence of vaccination efforts.
We evaluated estimates of age-specific influenza-attributable outcomes (ill-non medically attended, office-based outpatient visit, emergency department visits, hospitalizations and death) and associated productivity loss. Health outcome rates were applied to the 2015 U.S. population and multiplied by the relevant estimated unit costs for each outcome. We evaluated both direct healthcare costs and indirect costs (absenteeism from paid employment) reporting results from both a healthcare system and societal perspective. Results were presented in five age groups (<5 years, 5–17 years, 18–49 years, 50–64 years and ≥65 years of age).
The estimated average annual total economic burden of influenza to the healthcare system and society was $11.2 billion ($6.3–$25.3 billion). Direct medical costs were estimated to be $3.2 billion ($1.5–$11.7 billion) and indirect costs $8.0 billion ($4.8–$13.6 billion). These total costs were based on the estimated average numbers of (1) ill-non medically attended patients (21.6 million), (2) office-based outpatient visits (3.7 million), (3) emergency department visit (0.65 million) (4) hospitalizations (247.0 thousand), (5) deaths (36.3 thousand) and (6) days of productivity lost (20.1 million).
This study provides an updated estimate of the total economic burden of influenza in the U.S. Although we found a lower total cost than previously estimated, our results confirm that influenza is responsible for a substantial economic burden in the U.S.
Uptake of Influenza Vaccination and Missed Opportunities among Adults with High-Risk Conditions, United States, 2013
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Since 1960, the Advisory Committee on Immunization Practices has recommended influenza vaccination for adults with certain high-risk conditions because of increased risk for complications from influenza infection. We assessed national influenza vaccination among persons ages 18-64 years with high-risk conditions.
We analyzed data from the 2012 and 2013 National Health Interview Survey. The Kaplan-Meier survival analysis procedure was used to estimate the cumulative proportion of influenza vaccination among adults ages 18-64 years with high-risk conditions. Potential missed opportunities for influenza vaccination were also evaluated. Multivariable logistic regression and predictive marginal analyses were conducted to identify factors independently associated with vaccination.
Overall, 39.9 million adults ages 18-64 years (18.9%) had at least one high-risk condition. For adults ages 18-64 years with high-risk conditions, overall influenza vaccination coverage was 49.5%. Coverage among adults 50-64 years of age was significantly higher compared with those ages 18-49 years (59.3% vs 39.0%; P <.05). Among adults ages 18-64 years, coverage was 46.2% for those with chronic lung diseases, 50.5% for those with heart disease, 58.0% for those with diabetes, 62.5% for those with renal disease, and 56.4% for those with cancer. Overall, 90.1% reported at least one visit to a health care setting where vaccination could have been provided. Among adults ages 18-64 years with high-risk conditions, older age, being female, Hispanic ethnicity or Asian race, having one or more physician visits, a regular physician for health care, health insurance, and having ever received pneumococcal vaccination were independently associated with a higher likelihood of influenza vaccination. Being widowed/divorced/separated or never married and not being employed were independently associated with a lower likelihood of influenza vaccination.
Influenza vaccination coverage varies substantially by age and high-risk conditions but remains low. Approximately 50% of those with high-risk conditions remain unvaccinated. Health care providers should ensure they routinely assess influenza vaccination status, and recommend and offer vaccines to those with high-risk conditions.
Performances of statistical methods for the detection of seasonal influenza epidemics using a consensus-based gold standard
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Epidemiology of influenza

Abstract

Section snippets

Seasonality of influenza

Effect of influenza type and subtype and of age

Influenza impact: mortality and hospitalizations

Influenza morbidity and indirect protection

The Thucydides syndrome: a new hypothesis for the cause of the plague of Athens

N Engl J Med

Influenza: the new acquaintance

Ann Intern Med

Vital statistics

Influenza studies. I. On certain general statistical aspects of the 1918 epidemic in American cities

Public Health Rep

The influenza epidemic of 1918

Trans Actuarial Soc Am

Observations on mortality during the 1918 influenza pandemic

Clin Infect Dis

The epidemiology and clinical impact of pandemic influenza

Vaccine

Pandemic influenza in 1957

Am J Med Assoc

Pandemic versus epidemic influenza mortality: a pattern of changing age distribution

J Infect Dis

Influenza: quantifying morbidity and mortality

Am J Med

Excess pneumonia–influenza mortality by age and sex in three major influenza A 2 epidemics, United States, 1957–1958, 1960 and 1963

Am J Epidemiol

Morbidity and mortality characteristics of Asian strain influenza

Public Health Rep

The Tecumseh study of respiratory illness. IX. Occurrence of influenza in the community, 1966–1971

Am J Epidemiol

Tecumseh study of illness. XIII. Influenza infection and disease 1976–1981

Am J Epidemiol

Influenza-associated deaths among children in the United States 2003–2004

N Engl J Med

Influenza in Singapore: assessing the burden of illness in the community

Ann Acad Med Singapore

Influenza-related hospitalizations among children in Hong Kong

N Engl J Med

A community study of respiratory infections in the tropics. I. Description of the community and observations on the activity of certain respiratory agents

Am J Epidemiol

The guinea pig as a transmission model for human influenza viruses

PNAS

Influenza in Thailand: a case study for middle income countries

Vaccine

Impact of influenza epidemics on mortality in the United States from October 1973 to May 1985

Am J Public Health