Don't be surprised if, the next time you see your doctor, her medical advice to you sounds a little muffled.

The health officers of Sacramento and Yolo counties last summer issued a new rule that health care workers who don't receive a flu vaccine must wear a protective mask at work, all flu season long.

All four major health care systems in the region – Sutter, Kaiser Permanente, Mercy and the UC Davis Medical Center – are enforcing the rule.

Nationwide, 64 percent of health care workers got the shot last flu season.

The rates are much higher at hospitals, such as UC Davis, that require vaccination for their employees (except individuals who opt out for medical reasons).

Dr. Christian Sandrock, health officer of Yolo County and associate professor of medicine at UC Davis, explains the change:

Why are clinicians wearing masks this year when they didn't before?

It's basically a policy shift based on the idea that we want people to be vaccinated. You have to wear the mask every day you work for the duration of the flu season, like six weeks, and that can be burdensome and annoying for people. They might choose a one-time shot instead. And second, it's pushing the mask to people who really don't want the shot, for patient safety.

Who is at risk if clinicians don't wear masks, and how much risk?

The patients are the main ones at risk. How much? It's actually really hard to know. If you come in contact with an infected person and you're not vaccinated yourself, you have roughly a 15 to 20 percent chance of picking up the flu. It's not huge. The problem is most patients are medically vulnerable, so they're at a higher risk of complications from flu.

Why would a health care worker choose not to get a vaccine?

The normal excuses we hear are, "I get sick when I get the shot," or, "I never get sick and I don't need it," or, "Vaccines don't work." A handful of people, or less, will have an egg allergy or a prior reaction to the vaccination. It's pretty rare.

What are the consequences for a hospital if it doesn't enforce this?

There are none. We say it's mandated to use forceful language, but there's really not any consequence for the hospital from us in the Health Department. Outside of declaring it a public health crisis, I would not have the authority to force someone to wear a mask.

Is it necessary that workers wear masks everywhere, including non-medical settings like health education classes?

In the health care setting, yes, but outside of that, no. Obviously, if someone is sick, the best thing is not to wear a mask, but to stay home.

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