I called about 15 local hospitals about two weeks ago asking about volunteer work - not for break, but for next semester. Every place where I actually was able to talk to someone - I got lots of answering machines - made it clear that there was a minimum time requirement. Most seemed to require at least 4 hours a week, for a miniumun of 6 months. Others had a miniumum requirement that you would complete 50 hours. You most likely will have to go to an orientation as well. I talked to one hospital that wanted a letter of recommendation and an interview. The hospital I decided to volunteer at (Detroit Receiving) is making me go to two orientations, one for new volunteers and one for the ER. (My ER one is tomorrow, but if it keeps snowing, I might be waiting to go to the one in January!)
So while it may be possible for you to volunteer in a hospital, I'm going to guess that it probably won't be possible, unless you plan on commiting some time after the break. They might not even have any orientation sessions until after the holidays so you wouldn't be able to start during the break anyway. And like someone else said, you have to go through the health screening as well, and wait for the results.
If the hospital volunteering doesn't pan out, maybe you could find some other one-time opportunities to volunteer. With the holidays coming on, I'm sure there are a bunch of charitable events going on where you live, like Toys for Tots, or a Coat Drive, or maybe odd jobs in a homeless shelter or working in a soup kitchen for a day. These are things that you most likely wouldn't have to make a major time commitment to, and they probably need a lot of help right around now. Plus it will look great to adcoms and be a rewarding experience for you. I've heard that adcoms like to see both a history of volunteering at one place over time, and one-day stints. If you are determined to do something, I'm sure you can find somewhere to volunteer. I would start making calls as soon as possible though. You might also want to check out helping.org's
volunteer search which can help you find local places that need help. You can search for both ongoing and one-time jobs, and you can choose how far away you are willing to drive, etc. Hope this helps.
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^v^