Question: What is the best time to the get the flu shot, when it first comes out in the fall or closer to the holidays?

Dr. Hibberd’s answer:

Influenza vaccination is provided annually starting in September in the Northern Hemisphere. It’s best to have your vaccine before December, as it seems to take two to three weeks to induce sufficient immune response for your body to fight flu virus exposure. But it’s not too late to get a shot this year.

If you are younger, try to have the nasal mist vaccine, as this seems to be more effective than the injectable vaccine, though it is more expensive to purchase. In general, it is very difficult to be sure how effective the flu vaccine is going to be, as it is a pooled vaccine of selected influenza viruses that are believed to be both common and to represent the best cross of strains to produce the broadest immunity.

The problem with the flu vaccine is the influenza virus’s ability to change — called antigenic drift — and is the reason a uniform influenza vaccine is not available with the same components every year as with other vaccines. It is also why last year’s flu shot is no longer effective and why a booster phenomenon is not seen the way it is seen with other more consistent viral vaccines such as the poliovirus or HPV vaccines.

The real answer to your question: You should aim to have a flu shot at least three weeks before you’re exposed to the virus. Remember flu can strike any time of year, but the highest frequency is seen from October through May each year.