Health authorities urge the public to vaccinate because the more people who are vaccinated, the less likely communicable diseases are to spread or return to a typically unaffected population. Being vaccinated protects more than just the patient being immunized. In fact, being properly vaccinated cuts the risk of catching a contagious disease for everyone else around you, including your family, friends, and co-workers. The reason for this phenomenon is what is now commonly referred to as “herd immunity.”
The concept behind herd immunity is that giving a vaccine to one person will not only help protect them from getting infected, but will also help prevent the transmission of disease to others. Once herd immunity reaches a certain threshold, the disease is eventually eliminated from a population. When this elimination is achieved worldwide, the disease is said to be eradicated. The last disease to be eradicated worldwide was smallpox, in 1977.
Herd immunity is valuable because it protects those who are too young or too frail to be vaccinated. The only catch is that a large proportion of the population must be immunized for herd immunity to be effective. The opposition some parents have against vaccinating children, or the “antivaxx” movement, has been a huge challenge to achieving effective herd immunity. In fact, so-called antivaxxers are largely responsible for the spread of preventable diseases, such as measles, to communities with inadequate vaccination rates.
How Many People Need to Be Vaccinated for Herd Immunity to Work?
This varies depending on the infectious germ and how contagious it is. The more contagious a disease, the more people who will need to be vaccinated against it for herd immunity to work. For instance, one example of a highly contagious disease is measles. Once one person is infected, they can infect another 15 unvaccinated people. Because of the aggressiveness of measles, to achieve herd immunity, at least 90 to 95% of the population needs to be vaccinated. Less contagious diseases, such as polio, need a minimum of about 80-85% of the population vaccinated in order for herd immunity to work.
It should be noted that herd immunity doesn’t work for every disease and vaccination. For example, tetanus is not a contagious disease, so herd immunity doesn’t apply.
Why You Shouldn’t Rely on Herd Immunity
You may wonder why you should even bother immunizing your children and/or yourself if everyone around you has already been vaccinated. The best way to protect a person against being infected with a communicable disease is to vaccinate them directly, rather than relying on the indirect protection that herd immunity provides. If you or your child has not been vaccinated and comes into contact with the germ responsible for any given disease, you will be completely susceptible. It should also be noted that, for many diseases, young children are at the highest risk of catching the disease and have the most severe bouts of illness.
Herd immunity is valuable because it protects those who are either too young to be vaccinated or those with immune system problems that make vaccines unsafe. It doesn’t take much of a dip in the number of people vaccinated to make herd immunity less effective. For this reason, it’s extremely important to vaccinate your children to promote the eradication of preventable diseases.
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