The virus that causes shingles — varicella-zoster virus — is also the virus that causes chickenpox. Your doctor's concern about your daughter and grandchildren may stem from reports of rare cases in which people with no immunity to chickenpox — meaning they've never had chickenpox or the chickenpox vaccine — have caught varicella-zoster virus from children recently vaccinated with the chickenpox vaccine.
However, there are no documented cases of the varicella-zoster virus being transmitted from adults vaccinated with the shingles vaccine, according to the Centers for Disease Control and Prevention (CDC). Varicella-zoster vaccines are recommended for children to prevent chickenpox and for adults age 50 and older to prevent shingles, but the formulations are different, and the vaccines are not interchangeable.
According to the CDC, in normal circumstances it's unnecessary to avoid pregnant women and unvaccinated children after you get the shingles vaccine. However, if you develop a rash after you get the shingles vaccine, always take the precaution of keeping the rash covered until all the bumps crust over.
To develop shingles, you have to catch chickenpox first, which typically happens in childhood. When you get over chickenpox, the varicella-zoster virus stays in your body, but remains dormant, often for many years and possibly for life. As you age, though, there's an increasing risk that the virus will reactivate, resulting in shingles.