Vaccine effectiveness

A vaccine's ability to prevent a specific disease determines its effectiveness. Authorised vaccines are effective at preventing disease and protecting the population when administered correctly.

As with any medicine, no vaccine is 100% effective in every person vaccinated. Effectiveness in an individual depends on a number of factors. These include:

• their age;
• other diseases or conditions they may have;
• time since vaccination;
• previous contact with the disease;
• how the vaccine is given;
• the vaccine.

For example, the vaccine against measles, mumps and rubella (MMR) is highly effective at preventing disease. It typically provides lifelong protection and has an effectiveness of around 97-99% among healthy children who receive two doses.

In some circumstances, a person can still get a disease even after receiving the recommended doses of a vaccine against it. This is due to the person not developing sufficient protection against the disease or due to immunity decreasing over time. In these cases, however, the person's symptoms are often milder than they would have been without vaccination. They are also less likely to infect others.