A Grinch-like glitch in this year's flu vaccine may make it harder to combat the dreaded virus this season.

The Centers for Disease Control recently announced that the virus has mutated so the current shot may not be as effective as hoped in protecting against the altered strain of flu.

What to do? For advice, we turned to Mayo Clinic pediatrician and vaccine researcher Dr. Robert Jacobson.

Q: How effective is the current flu shot?

A: What we know so far is that the virus is different from what we expected. It's what we call "genetically drifted."

It will be a year or so before we have good data on the true effectiveness. But we suspect it will be like in past years when there were drift variants and the vaccine's effectiveness dropped.

About half of the infections we're seeing look like they have genetically drifted away from what we designed the vaccine to be. That's frustrating and would suggest that we might be in for a rough influenza season.

Q: What happens when a virus "genetically drifts"?

A: Actually, this is the problem that we have year after year with the flu viruses. Influenza A has two major strains against which we vaccinate, including H1N1 and H3N2. Both of those each year either genetically drift or genetically shift. When they shift, they change so much that an overwhelming majority of the population doesn't have any immunity against them. In those years, it causes a pandemic.

The drift happens in part because as humans get immune to last year's infection, the only way for the virus to replicate is to evolve and change its genes. The mutations survive, while the old versions can't replicate and reproduce, so they disappear.

Around January or February, the World Health Organization and the Food and Drug Administration look at what's happening and inform manufacturers on what they want [made]. The manufacturers then begin the work of growing the viruses in eggs. It takes months and months to grow this year's vaccine supply.

It's not that the manufacturers got it wrong. About every three years we have a problem with the match of one of the strains. Over the last 10 years we've had at least three bad seasons where the H3N2 was a mismatch and we see an increased rate of hospitalization and death.

Q: What are some things people can do to protect themselves given that the shot may not work as well this season?

A: First of all, you should still get your flu shot! People who get the flu shot have better protection even when there's a mismatch. They often get less severe a case of the flu and they're less likely to spread the flu to someone else. Frankly, 35 percent effectiveness is better than nothing.

Second, if you're sick, don't go to work. If you're sick, don't go to school. You might feel up to working and you may even feel like you're doing your colleagues a favor by showing up for work, but you're actually spreading the disease.

Q: Flu season has arrived at the busiest time of the year. Is this typical?

A: We started early this year in Minnesota. We're now three or four weeks into seeing increased rates of flu disease among those patients with fever and cough. About 30 percent of our tests for influenza have come back positive.

Thanksgiving and the holidays make it tough because large groups of people who haven't seen each other get together, share germs and then everyone goes back to work and school.

As much as you want to celebrate the holidays with family and friends, if you've got a cough and fever or a sore throat and fever, stay in bed and stay home.