Vaccination should occur before onset of influenza activity in the community, as it takes about two weeks after vaccination for antibodies to develop in the body that protect against flu virus infection. It is recommended that vaccination should be received by the end of October. Flu season is unpredictable, it is not like a hunting season and has a set start date. However, because timing of the onset, peak, and decline of influenza activity varies, the ideal time to start vaccinating cannot be predicted each season. Children aged 6 months through 8 years who require 2 doses should receive their first dose as soon as possible after the vaccine becomes available to allow the second dose (which must be administered ≥4 weeks later) to be received by the end of October. 

Did you know?

The CDC estimated that, from October 1, 2018, through May 4, 2019, there were:

  • 4 million – 42.9 million flu illnesses
  • 3 million – 20.1 million flu medical visits
  • 531,000 – 647,000 flu hospitalizations
  • 36,400 – 61,200 flu deaths 

Who is recommended for Vaccination?

An annual influenza vaccination is recommended for all persons aged ≥6 months who do not have contraindications. Preventing the flu is particularly important for people who are at high risk of serious complications from the influenza virus.

Are you Traveling?

Travelers who want to reduce the risk for influenza infection should consider influenza vaccination, preferably at least 2 weeks before departure. In particular, persons who live in the United States and are at higher risk for complications of influenza and who were not vaccinated with influenza vaccine during the previous Northern Hemisphere fall or winter should consider receiving influenza vaccine before departure if they plan to travel to the tropics, with organized tourist groups or on cruise ships, or to the Southern Hemisphere during the Southern Hemisphere influenza season (April–September).

Persons at higher risk who received the previous season’s vaccine before travel should consult with their health care provider to discuss the risk for influenza or other travel-related diseases before embarking on travel during the summer. All persons vaccinated before travel should receive the current vaccine the following fall or winter.

In temperate climate regions of the Northern and Southern hemispheres, influenza activity is seasonal, occurring approximately from October through May in the Northern Hemisphere and April through September in the Southern Hemisphere. In the tropics, influenza might occur throughout the year. Travelers can be exposed to influenza when traveling to an area where influenza is circulating or when traveling as part of large tourist groups (e.g., on cruise ships) that include persons from areas of the world in which influenza viruses are circulating.