Dr J. Kevin Yin and Dr Melina Georgousakis explain how vaccination not only protects the individual who gets the vaccine, but also other people in the community through 'herd protection'.
How does herd protection work?
When a large number of people in a community are vaccinated and therefore immune to a disease, it reduces the ability of that disease to spread. This means those who haven't been vaccinated get some protection. This is called herd protection (also known as 'herd immunity'). For herd protection to occur, a certain number of people in the community must be vaccinated (or immune). If the number drops, herd protection is broken and the disease can spread again.
Herd protection is especially important for those who can't get vaccines, such as people with certain medical conditions, or infants who are too young.
Herd protection prevents disease outbreaks
Recent outbreaks of measles have occurred in Australia in areas where vaccine coverage is low and herd protection has been broken.
Measles is a highly contagious disease, which is easily passed between people by respiratory droplets, for example, when we cough. Most people with measles have flu-like symptoms followed by a rash. Around one in three develop complications, with many requiring hospitalisation.
Due to the majority of Australians receiving the measles vaccine, or for older Australians, having measles as a child, Australia has been declared 'measles free' by the World Health Organization. This means measles no longer naturally circulates in Australia. However, measles outbreaks still occur from travellers who are not fully vaccinated picking up the virus in a country where measles is common and bringing it back to Australia. When this happens, measles can spread rapidly in communities where not enough people are vaccinated, which is what has led to the recent outbreaks. Thankfully these outbreaks haven't spread too far because most Australians are vaccinated, which blocks the spread of the virus. However, if the level of people vaccinated in the community drops, there's greater risk the virus can spread as herd protection is broken.
Check you and your family members are up-to-date
For measles, two doses of vaccine are recommended: the first dose is given at 12 months of age as the measles-mumps and rubella (MMR) vaccine and the second dose at 18 months as the measles-mumps-rubella-varicella (MMRV) vaccine. Some adolescents and adults may have missed out on receiving their second dose of measles vaccine, so it's important to check with your doctor. This is particularly important as it's this age group that's more likely to travel and could bring the measles virus back into Australia.
Dr Melina Georgousakis and Dr J. Kevin Yin are senior research officers at the National Centre for Immunisation Research and Surveillance, Sydney.