Influenza

Seasonal influenza is an acute respiratory infection caused by influenza viruses that circulate worldwide. There are four types of seasonal influenza viruses: types A, B, C, and D. Influenza A and B viruses circulate and cause seasonal epidemics of the disease.Seasonal influenza is characterized by a sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat, and a runny nose. The cough can be severe and may last two weeks or longer.  

Epidemics can lead to high rates of absenteeism from work or school and a loss of productivity. Research estimates that 99% deaths among children under the age of 5 due to influenza-associated lower respiratory tract infections occur in developing countries. Age group L may be affected by the influenza virus. 

The most effective way to prevent disease is vaccination. The vaccine is safe and effective. Among healthy adults, the flu vaccine provides protection, even when the circulating virus is not exactly the same as the one in the vaccine. The flu vaccine causes antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against the virus strains included in the vaccine.

Traditional flu vaccines (called “trivalent” vaccines) are formulated to protect against three flu viruses: influenza A (H1N1), influenza A (H3N2), and influenza B. There are also flu vaccines formulated to protect against four flu viruses (called “quadrivalent” vaccines). These vaccines protect against the same viruses as the trivalent vaccine, plus an additional influenza B virus. Flu vaccines are needed every season for two reasons. First, the body’s immune response to vaccination wanes over time, so an annual vaccine is necessary for optimal protection. Second, because flu viruses are constantly changing, the composition of the flu vaccine is reviewed annually and sometimes updated to keep pace with changes in the flu viruses. For the best protection, everyone 6 months of age and older should get vaccinated every year.

The flu vaccine has important benefits. This can reduce the incidence of the flu, doctor visits, and absences from work and school due to the flu, as well as prevent flu-related hospitalizations.