Do you need a tetanus shot if you spent any time in floodwaters?
You only need a tetanus shot – ASAP – if you exposed an open wound to floodwaters. Of course, unless you've had a tetanus shot in the last 10 years, you probably need a booster shot, but there's no rush, particularly given the stresses Harvey will put on the health-care system.
People with puncture wounds or cuts exposed to floodwater could be at risk of contracting tetanus and may need to have a tetanus shot to prevent infection.
More info: https://www.cdc.gov/tetanus/about/index.html