It is possible, in what’s called breakthrough varicella. However, chickenpox in those who have been vaccinated is less contagious and results in less severe symptoms. Those who contract it generally have a low fever or no fever at all and develop fewer than 50 lesions. Among people who received only one dose of the vaccine and have breakthrough infection, 25% to 30% will develop symptoms as if they had not been vaccinated, which is why two doses are recommended.