Seasonal influenza viruses circulate worldwide and can affect people in any age group. In temperate climates, influenza in young children epidemics occur mainly during winter while in tropical regions, influenza seasonality is less obvious and epidemics can occur throughout the year.
Seasonal influenza is a serious public health problem that causes severe illness and death in high risk populations. An influenza epidemic can take an economic toll through lost workforce productivity and strained health services. Influenza vaccination is the most effective way to prevent disease. Antiviral drugs are available for treatment. Influenza A and B viruses circulate and cause seasonal epidemics of disease.
Influenza B viruses are not classified into subtypes, but can be broken down into lineages. Influenza C virus is detected less frequently and usually causes mild infections, thus does not present public health importance. Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people. The cough can be severe and can last 2 or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention. Illnesses range from mild to severe and even death. Hospitalization and death occur mainly among high risk groups.
Worldwide, these annual epidemics are estimated to result in about 3 to 5 million cases of severe illness, and about 290 000 to 650 000 respiratory deaths. Clinics and hospitals can be overwhelmed during peak illness periods. Health care workers are at high risk acquiring influenza virus infection due to increased exposure to the patients and risk further spread particularly to vulnerable individuals. In terms of transmission, seasonal influenza spreads easily, with rapid transmission in crowded areas including schools and nursing homes. The virus can also be spread by hands contaminated with influenza viruses.
In temperate climates, seasonal epidemics occur mainly during winter, while in tropical regions, influenza may occur throughout the year, causing outbreaks more irregularly. The time from infection to illness, known as the incubation period, is about 2 days, but ranges from one to four days. However, during periods of low influenza activity and outside of epidemics situations, the infection of other respiratory viruses e. Treatment focuses on relieving symptoms of influenza such as fever.
Administration of the drug should also be considered in patients presenting later in the course of illness. Treatment is recommended for a minimum of 5 days, but can be extended until there is satisfactory clinical improvement. WHO GISRS monitors resistance to antivirals among circulating influenza viruses to provide timely guidance for antiviral use in clinical management and potential chemoprophylaxis. Safe and effective vaccines are available and have been used for more than 60 years. Immunity from vaccination wanes over time so annual vaccination is recommended to protect against influenza.
Injected inactivated influenza vaccines are most commonly used throughout the world. Influenza vaccine is most effective when circulating viruses are well-matched with viruses contained in vaccines. Estimates of US influenza-associated deaths made using four different methods. Thompson WW, Weintraub E, Dhankhar P, Cheng OY, Brammer L, Meltzer MI, et al.