Is Australia at risk of losing its herd immunity with lower vaccination rates? The measles vaccine contains a very weakened form of measles virus. The measles "herd immunity threshold" is 93-95% in the total population. To maintain herd immunity, we need to ensure all adults under 60 and children from one year are two dose measles vaccinated. In Australia, free catch-up measles vaccination is available for anyone born after 1966 who doesn't have proof of two doses of measles vaccine.