An inactivated vaccine, also known as a killed-virus vaccine, is a non-cancerous vaccine containing microbe or virus fragments that have been grown in vitro and then destroyed so as not to cause disease. Whereas live vaccines use living microbe viruses, these vaccines use microbe fragments that have become inactive after being in existence for some length of time. These live viruses can cause outbreaks of illness similar to those that occur with natural immunity. An example of this vaccine is Gardasil, the smallpox vaccination.
Many health care professionals agree that although inactivated vaccines are more economical than live vaccines, they are not any less safe. The main reason for this is that inactivated viruses are slower to replicate than the living variety; therefore, the quantity of strain that an unaltered virus can circulate in a human population is smaller than it would be with natural immunity. Since the introduction of new vaccines, inactivated vaccines have seen a steady decline in the number of cases of illness associated with them. However, in the past decade, there has been a resurgence in reported cases of illness following the installation of HPV vaccines. Some experts believe this is due to an increase in sexual activity and sexual behaviors that might include unprotected sex with an infected partner.