Why did I still get sick even after I got a flu shot?
The ability of the flu vaccine to protect a person depends on two things:
  1. The age and health status of the person getting vaccinated
  2. The similarity or “match” between the virus strains in the vaccine and those circulating in the community

If the viruses in the vaccine and the influenza viruses circulating in the community are closely matched, vaccine effectiveness is higher. If they are not closely matched, vaccine effectiveness can be reduced. However, it’s important to remember that even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Such protection is possible because antibodies made in response to the vaccine can provide some protection (called cross-protection) against different, but related strains of influenza viruses.

Show All Answers

1. How do I know that I have the flu?
2. How does the flu spread?
3. How long is a person with flu virus contagious?
4. Can the flu be treated?
5. Why should people get vaccinated against the flu?
6. When should I get a flu vaccine?
7. How do flu vaccines work?
8. Is the “stomach flu” really the flu?
9. How many people get the flu each year?
10. Do other respiratory viruses circulate during the flu season?
11. How soon will I get sick if I’m exposed to the flu?
12. How do scientists determine which strains to protect against in a flu vaccine?
13. Can a flu vaccine give you the flu?
14. Why do I feel sick after getting a flu shot?
15. Why did I still get sick even after I got a flu shot?
16. Do I need to get a flu vaccine every year, or will the immunity carry over from last year’s vaccine?
17. Is it ever too early or too late to get a flu vaccine?
18. How can I learn more about the progress of the flu season?