Uber users in more than a dozen major cities across the US will have the opportunity to score a free flu shot for themselves and up to four others. Here's everything you need to know.

According to Uber health care advisor Dr. John Brownstein, PhD, the flu affects 20 percent of the population. Every person that receives an influenza vaccine, Brownstein says, reduces the risk of others contracting the virus by as much as 60 percent. It's this statistic that Uber is hoping to build on with its latest promotion.

On Tuesday (October 25) from 11 a.m. to 3 p.m. (I'm assuming local time since Uber didn't specify), users are invited to open the Uber app and request the "Health" option. This should grant you a free care package and the option to receive the Fluzone vaccine for you and up to four others.

Once complete, Uber says to "pick a comfy spot" and a registered nurse from Passport Health will administer the shot(s) and handle all of the necessary paperwork.

This year, the promotion is being offered in the following cities: Albany, NY; Baltimore, MD; Boston, MA; Birmingham, AL; Chicago, IL; Columbus, OH; Hartford, CT; Wilmington, DE; Houston, TX; Jacksonville, FL; Manchester, NH; Portland, ME; Providence, RI; Syracuse, NY; Tallahassee, FL; Washington, DC.

The transportation company hosted a similar promotion last year in which it charged users $10 for a wellness package that included flu shots for up to 10 people.

Uber warns that demand will likely be high this year and asks for your patience.