Each year, the vaccine is updated to include the most current influenza virus strains. This is why it is necessary to get the flu shot every year. Influenza usually occurs in the United States each year from October until April. Activity is typically low until December, and usually peaks between January and March. It takes one to two weeks from the time of vaccination to develop antibodies and provide protection.
Some circumstances warrant the use of antivirals to prevent influenza.
Both are very effective in preventing illnesses caused by only type A influenza viruses. For maximum effectiveness, the drug must be taken each day for the duration of influenza activity in the community. Persons who cannot be vaccinated. Chemoprophylaxis may be considered for these persons during the period of peak influenza activity. Prophylaxis should be considered for all healthcare employees, regardless of their vaccination status, if the outbreak is caused by a variant strain of influenza that might not be controlled by the vaccine.