Chickenpox (varicella) is a viral infection caused by the varicella-zoster virus. Shingles (herpes zoster infection) is caused by re-activation of the chicken-pox. 
 
Chickenpox (also known as "Varicella") is a common childhood disease. It is usually mild, but can be serious in young infants and older adults. The chickenpox virus spreads from person to person through the air, or by contact with the fluid from the blisters on the body.
 
Chickenpox vaccination should be used with caution if you come in regular contact with pregnant women (who have never had chickenpox or have never received vaccination), or people with a weak immune system. This is because the vaccine can cause (although rare) small spots and blisters which are infectious to appear on the body.
 
Women who are pregnant should not receive the chickenpox vaccine. Pregnancy should also be avoided for one month after vaccination. The vaccine consists of two doses which are given six weeks apart.