“The flu vaccine is safe for most people and is recommended for everyone ages 6 months and older. People who should not receive flu vaccines are those who have had a severe allergic reaction to the flu or other vaccine in the past and those who have had a condition called Guillan-Barre syndrome.   Make a plan to get vaccinated and why is because of the following.  You should get a flu vaccine before flu viruses begin spreading in your community since it takes about two weeks after vaccination for antibodies to develop in the body and provide protection against flu.  A flu vaccine is needed every season for two reasons. First, a person’s immune protection from vaccination declines over time, so an annual vaccine is needed for optimal protection. Second, because flu viruses are constantly changing, flu vaccines may be updated from one season to the next to protect against the viruses that research suggests may be most common during the upcoming flu season.”.

Baltimore City Health Dept (https://health.baltimorecity.gov/flu/frequently-asked-questions-about-flu-vaccines)