Influenza, caused by one of the four virus types A, B, C and D, is a common respiratory infection. While influenza strains A and B cause typical flu symptoms, C is milder, and D has so far not been detected in humans. Influenza, or “flu” as its often referred to, returns regularly in the winter season and affects a large part of the population. Influenza can have severe effects and even lead to excess in mortality among the elderly and frail patients.
Influenza virus can spread by aerosols, infected water droplets, or direct contact. Individuals considered in ‘high risk’ groups (e.g. the elderly) are encouraged to take an annual vaccination against influenza, as a previous infection may not give protection against a new infection. This is because influenza viruses, primarily found in the throat and airways, mutate (change) regularly. This ability can lead to more extensive outbreaks or even, potentially, pandemics. Perhaps the most well-known influenza pandemic was the so-called ‘Spanish Flu’, which occurred during WWI. It had large effect on society and the health of people worldwide. Given the potential negative effects of influenza on public health, continuous efforts are made to monitor its spread and to develop vaccines against novel strains. For more information related to influenza and how it is managed in Sweden, refer to The Swedish Public Health Agency (resources in Swedish).