This year’s flu season is shaping up to be a bad one. Much of the country endured a bitterly cold stretch, causing more people to be crowded together inside. The strain that has been most pervasive, H3N2, is nastier than most. And, we’re being told, the vaccine this year is particularly ineffective.

That last fact has had many people wondering if they should still get a flu shot. If you read no further in this column, know this: The answer is yes, you should still get a flu shot. The flu season typically peaks December through February but can last until May, and it usually takes about two weeks for the shot’s immunity to kick in.

It’s worth exploring what we mean by effectiveness when we’re discussing the flu vaccine.

The flu virus is unstable, and it changes a lot each season. This means that the immunity you gained from a shot a year ago doesn’t work so well this time around. Each summer, scientists gather and try to make a best guess on which variants are going to be more common in the coming year. They look at data from countries like Australia (whose flu season comes before ours), then they make the shot to match.

This season, the flu vaccine is most protective against an H1NI, an H3N2 and a B/Victoria lineage strain. Some vaccines also protect against a B/Yamagata lineage strain.