Should I get a flu vaccine this year even if last year’s vaccine didn’t prevent me from getting the flu?

DEAR DOCTOR K:

I got the flu vaccine last year and still got the flu. Should I even bother with the flu vaccine this late?

DEAR READER:

Yes, you should, but don’t expect perfect protection this year, any more than you should have last year. Vaccines contain fragments of three or four strains that are predicted to dominate during the coming flu season. Different strains of the virus circulate each flu season (October-May).

Huge amounts of flu vaccine need to be made each year. That means that production of the vaccine must begin about six months before the flu season starts, in order to make enough for everyone. As a result, the doctors and scientists responsible for developing the next year’s vaccine need to guess at which strains of the virus will be circulating six to nine months later. They make an educated guess, but it’s still a guess. No one has a crystal ball.

Last year’s flu vaccine was partially effective, but not as effective as usual, because early in the 2014-15 season, a new flu strain emerged. As the vaccine did not include the new strain, the vaccine’s overall effectiveness was only about 20 percent. In a good year, the effectiveness can be 60 percent or greater.

But don’t let last year’s experience put you off of vaccination. The flu vaccine always reduces the risk of illness — just more so in some seasons than in others.

Some of my patients don’t get flu shots, despite my recommendation to do so. Sometimes the reason is that they don’t believe the vaccine will really protect them, although that clearly is wrong.

Equally often, they think of the flu as an illness like the common cold: some sneezing, sniffles and coughing for a few days. Sometimes influenza is that mild. However, usually it is much more severe. In fact, 25,000 to 40,000 people die each year in the United States from influenza.

In most years, the people most likely to get severely ill are older adults or people with chronic diseases. These include people with lung disease, heart disease, dementia, diabetes and kidney or liver disease.

Besides protecting yourself, a flu shot makes you less likely to infect someone else, such as an aging or chronically ill parent or grandparent.

The Centers for Disease Control recommends vaccination every year for everyone aged 6 months and older. Flu shots contain inactive, killed virus; you cannot get the flu from this vaccine. There is also an inhalable (nasal) vaccine that contains live, weakened virus. A new, high-dose version of the flu vaccine is intended to help older adults mount a stronger defense against the flu.

Get vaccinated as early as you can — like this week. It takes two to four weeks after you get the shot to build immunity. During this time, you can still be infected by the flu.

Someday we may have a flu vaccine that is close to perfect. Until that time, getting partial protection is better than having no protection at all against a potentially fatal disease.