Dear Vaccine Smarts,
I recently heard news reports on children’s vaccination rates falling in Oregon and the recent outbreak of measles in Texas. Health officials were worried that disease rates would start rising due to a loss of herd immunity. Can you please explain herd immunity?
Caesar, League City
There has been quite a bit of buzz about parents opting out of vaccinating their children in Oregon and in certain communities in California and Texas.
As a result, Oregon approved a law requiring that parents speak to a doctor or watch an educational video before sending their kids to public school without receiving their vaccinations.
The reasoning behind the law is that unimmunized individuals place others at risk. It is important to understand that vaccines are not effective in 100 percent of the population; that is to say, that not everyone who is vaccinated responds.
“Non-responders” are not protected because they don’t have a good immune response. Vaccination response rates vary but in general they are about 90 percent.
Let’s say an entire population consists of 100 people who are all vaccinated.
Out of these 100 people, 90 are protected and 10 did not have a good enough immune response to be fully protected.
Luckily, it turns out that the 10 people who didn’t respond are protected indirectly by the other 90 vaccinated people because they are disease-free and can’t spread the disease to the 10 non-responders.
This phenomenon is called “herd immunity.”
The disease can’t spread within the population because most of the members are immune.
Herd immunity becomes weaker as the number of protected individuals drops. Parents who choose not to vaccinate their children and send them to school place everyone at risk.
These unvaccinated children benefit from herd immunity, but when the community’s numbers of unvaccinated children become high enough, disease can spread freely.
This places the vaccinated students who didn’t respond to vaccination at risk. It also places at risk those students who can’t be vaccinated because of medical conditions such as cancer or immune deficiencies.
According to recent reports, the measles outbreaks in Texas began with someone who traveled to another country where measles is prevalent. The person returned and introduced measles into a community with a low immunization rate. Reports also mention that a 4 month-old baby who was too young to be vaccinated caught measles at church. It’s recommended that non-immunocompromised children receive two vaccinations, the first one at 12 months of age and the second (booster) around 4 to 6 years of age. Adults who travel out of the country should also talk to their physician about receiving a measles booster before their trip.
The person who infected these people did so unknowingly because it takes a week before symptoms to appear.
This situation is tragic, but some argue that it’s the parents’ right to not vaccinate their child. Others feel that it’s wrong for these parents to place other children at risk.
Perhaps the Oregon law requiring parent education on vaccination is a good compromise and will help maintain herd immunity. Only time will tell.