Herd immunity and vaccine problems.

I know I post about this all the time, but it impacts our lives in so many ways. Vaccines help protect the helpless. Children under the age of one year old are too young to be vaccinated by the MMR vaccine. Measles kills and harms children. Data to support this? A recent report out of Europe has indicated that last year eight peopele died and 29 had encephalitis related to measles infections.  The population with the highest incidence of serious disease?  Children under the age of one. These children cannot be vaccinated. But they became infected because other individuals, who could be vaccinated were NOT vaccinated, no herd immunity.

Herd immunity is a hard concept to understand. But let’s try to understand it from the scenario above: You have a baby who cannot be vaccinated (too young/immune system weak to survive even an attenuated measles infection).  Measles is a virus that can ONLY infect humans. If you have been vaccinated, the virus CANNOT infect you and you CANNOT infect your child. If everyone who comes into contact with the child also has been vaccinated, they CANNOT be infected with measles virus and therefore CANNOT infect your child. There is no virus in the environment and no place for the virus to be.

So, you have all the individuals surrounding your child vaccinated. This effectively creates a barrier around the child where no virus can lurk.  Measles can only infect humans, no humans around can be infected, no infection, no reservoir for infection.

But what happens if  you accidentally come into contact with someone who doesn’t vaccinate themselves and their children? This puts a hole in the barrier to infection. This gives a place where the virus can grow and replicate. It creates a reservoir of infection.

How to prevent this reservoir? According to statistics, for herd immunity to protect our most vulnerable, anywhere from 80-95% of the population has to be vaccinated to prevent transmission to at risk individuals. The range differs between pathogens, and depends on their mode of transmission. Measles is very transmissible in that it can be spread in the air through respiratory droplets.

The EU had tried to wipe measles out by 2010 by trying to vaccinate 95% of their entire population with at least two doses of vaccine. That goal was unattainable, and they are now pushing for elimination by 2015. But recent upsurge of infection makes even a goal of 2015. Just look to the chart detailing measles infections in France from the last 5 years.

measles cases in FranceWhy are we seeing so many cases of measles? Fear of vaccination? Inability to get vaccines due to lack of health care? Fear of doctors? Probably all of the above. However, today there is new data being reported that a chemical  we are putting into our environment may be making our vaccines less effective, and herd immunity less attainable.

Herd immunity protects those who can’t protect themselves.  Vaccines are a necessary, vital aspect of protecting those individuals.

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