2Does getting vaccinated against flu early in the season pose a risk that immunity may wane before the end of the season? No. Flu vaccination provides protection against the influenza strains contained in the seasonal vaccine for the entire season. Vaccination can begin as soon as vaccine becomes available.

Is it too late to get vaccinated after Thanksgiving (or the end of November)? No. CDC recommends that providers begin to offer seasonal influenza vaccination as soon as vaccine becomes available in the fall, but if you have not been vaccinated by Thanksgiving (or the end of November), it can still be protective to get vaccinated in December or later because influenza disease usually peaks in January or February most years, and disease can occur as late as May.

Does flu vaccine work right away? No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. In the meantime, you are still at risk for getting the flu. That's why it's better to get vaccinated early in the fall, before the flu season really gets under way.

Why do I need to get vaccinated against the flu every year?

There are two reasons for getting a yearly flu vaccine:

Ÿ The first reason is that because flu viruses are constantly changing, flu vaccines may be updated from one season to the next to protect against the most recent and most commonly circulating viruses.

Ÿ The second reason that annual vaccination is recommended is that a person's immune protection from vaccination declines over time and annual vaccination is needed for optimal protection.

The decline in protection against the flu that occurs after vaccination or after flu infection may be influenced by several factors, including a person's age, the antigen used in the vaccine, and the person's health situation (for example, chronic health conditions that weaken the immune system may have an impact). This decline in protection has the potential to leave some people more vulnerable to infection, illness and possibly serious complications from the same influenza viruses a year after being vaccinated.

So, for optimal protection against influenza, annual vaccination is recommended regardless of whether the viruses in the vaccine have changed or not since the previous season.

Source: U.S. Centers for Disease Control and Prevention