Vaccines are remarkably safe and effective, although some children occasionally experience minor reactions to them. The first vaccine that an infant receives is of hepatitis B, and the first dose of hepatitis B vaccine is given during the first week of life, sometimes when the infant is still in the hospital. Other routine immunisations begin at 6 to 8 weeks, or somewhat later if the infant is ill. Immunization need not be delayed, however, if the infant has a slight fever from a mild infection such as an ordinary cold.
Many vaccines require more than one dose to provide full immunity.
However, the recommended ages for immunisations should not be construed as absolute. For example, two months can mean 6 to 10 weeks. Though parents should try to have their children vaccinated according to a schedule, some delay doesn't interfere with the final immunity achieved nor does it entail restarting the series of injections from the beginning. Some vaccines are recommended under special circumstances. For example, hepatitis A vaccine may be recommended for people going to college or for those traveling overseas.