Seasonal influenza

Seasonal influenza is a contagious respiratory disease caused by an influenza virus. It is not the same as a common cold. Influenza is characterized by a sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), a sore throat and a runny nose. The cough can be severe and can last 2 or more weeks. Influenza cannot be treated with antibiotics. Severe cases of influenza may be treated by antivirals under the supervision of a doctor. The best protection against influenza is vaccination.

Most people recover from fever and other symptoms within a week without requiring medical attention. However, influenza can cause severe disease and death, especially in people over 65, young children, pregnant women and people with long-term health conditions. Every year, people in these at-risk groups die from influenza. Worldwide, up to 650 000 people die of respiratory diseases linked to seasonal influenza each year, and up to 72 000 of these deaths are in the WHO European Region.

When influenza starts to spread every winter, WHO strongly recommends that certain groups be vaccinated against the disease. These include:

• pregnant women;
• individuals with chronic heart or lung diseases, metabolic or renal disease, chronic liver disease, chronic neurological conditions or immunodeficiencies;
• people over a nationally defined age limit, irrespective of other risk factors (typically people over 65);
• residents of long-term care facilities for older people and the disabled;
• children aged 6–59 months; and
• health-care workers, including those who work in facilities that care for older people or people with disabilities.

• regular handwashing and proper drying of hands;
• good respiratory hygiene (covering the mouth and nose when coughing or sneezing, and using tissues and disposing of them correctly);
• early self-isolation when feeling unwell or feverish, or when experiencing other symptoms of influenza;
• avoidance of close contact with sick people; and
• avoidance of touching the eyes, nose or mouth.

It is best to get vaccinated before the influenza season starts. Influenza vaccination campaigns usually take place around October, soon after the vaccine becomes available. After receiving the vaccine, it takes 2 weeks to develop protective antibodies against influenza. However, it is never too late to be vaccinated if influenza is still circulating. Vaccination increases the chances of being protected from infection and may lessen severe consequences of the disease.

WHO recommends prioritizing vaccination for older individuals, young children, pregnant women and people with underlying health conditions because these are the groups most likely to suffer serious complications from influenza. However, anyone can catch influenza, and healthy working-age adults can also be vaccinated. In the case of health-care workers, they need to be vaccinated to protect themselves and to reduce their risk of infecting vulnerable patients with the virus.

So far, trivalent vaccines have been the most widely used vaccines in Europe. Trivalent vaccines protect against 3 influenza viruses – usually 2 type A viruses and 1 type B virus. Discussions on the advantages of shifting to quadrivalent vaccines, which protect against 2 type A and 2 type B viruses, are ongoing. Quadrivalent vaccines are more expensive, but studies in some countries have shown that they may be cost-effective if overall costs for the health-care sector are taken into account. However, the economic background varies from country to country.

WHO makes a recommendation of what should go into the vaccine each year to target the viruses that are expected to circulate in the coming season. The recommendation is based on information from the WHO Global Influenza Surveillance and Response System, the body responsible for monitoring the types of viruses circulating and rapidly identifying new strains. WHO also takes into consideration vaccine effectiveness in previous and current influenza seasons.

Influenza vaccines are most commonly made using an egg-based manufacturing process. This process has been used for more than 70 years. The egg-based process produces both the inactivated (killed virus) vaccine, which is the most common version and is given by injection, and the live attenuated (weakened virus) vaccine, which is given as a nasal spray.

The A(H1N1) virus, which caused the influenza pandemic in 2009, has continued to circulate in people in Europe and elsewhere and is now a seasonal human influenza virus. In 2009, the global population had little immunity to A(H1N1) because it was new. It caused a global epidemic and was responsible for an estimated 100 000 to 400 000 deaths that year. The A(H1N1) virus now circulates as a seasonal influenza virus. The seasonal influenza vaccine provides protection against A(H1N1). Flu News Europe provides a weekly overview and assessment of influenza activity in the WHO European Region based on surveillance data from the Region’s 53 Member States: http://flunewseurope.org/

The A(H1N1) virus now circulates as a seasonal human influenza virus. It has not changed significantly from the 2009 virus, and there is no evidence that it has become more harmful. Since its emergence in 2009, the A(H1N1) virus has caused rare cases of severe disease in otherwise healthy, young adults, including pregnant women. In contrast, the A(H3N2) virus is more likely to cause severe disease and death in older people. Clinicians must be aware of this so they can administer early treatment with an influenza antiviral drug (oseltamivir) to patients who show severe respiratory symptoms. WHO has prepared advice for European clinicians on managing severe complications of influenza.