How soon after their first dose should people who remain at risk for meningococcal disease be vaccinated again?

3-5 Years. It depends on your age. Children under 7 should wait at least 3 years. Anyone 7 or older, 5 years.
10-15 years. The military uses 10-15 years as a range. Not aware of any specific guideline for this, but reasonable.

Related Questions

Should college students be vaccinated against meningococcal disease?

YES. Yes, but the peak risk actually starts rising around 13-14 yo and kids should be getting this shot at 11 yo now. Currently the CDC says to get one at 11 yo and another at 16 yo. Read more...
Absolutely. It is particularly devastating illness that is easily transmitted between persons in close proximity, and appears easier in teens/twenties. All should be vaccinated. Read more...