Previous vaccination with the varicella vaccine does not always guarantee that a person will not develop chickenpox symptoms. However, if they do, these symptoms are usually much milder than in an unvaccinated person. About 15% – 20% of people who have received one dose of varicella vaccine will still get chickenpox if they are exposed to the virus. Children who have received two doses of the vaccine have a less than 7% chance of getting chickenpox.