Sheila M. Martin-Corbin
Herd Immunity
(adapted from: www.cdc.gov/scienceambassador/lesson-plans/2013-herd-immunity.pdf and http://www.ovg.ox.ac.uk/herd-immunity)
When a high percentage of the population is vaccinated, it is difficult for infectious diseases to spread because there are not many people who can be infected. For example, if someone with measles is surrounded by people who are vaccinated against measles, the disease cannot easily be passed on to anyone, and it will quickly disappear again. This is called ‘herd immunity’, and it gives protection to vulnerable people such as newborn babies, elderly people and those who are too sick to be vaccinated.
However, "herd immunity" does not always protect people against those diseases which can be prevented by use of a vaccine. For example, tetanus, is caught from a bacteria in the environment, not from other people with the disease. Therefore, regardless of how many people around you are vaccinated against tetanus, this population of people will not protect other people from being inflicted with tetanus. Herd immunity is only effective when most people in the population are vaccinated against the disease. If people are not vaccinated, herd immunity is not guaranteed to protect them.
If you live in an area where vaccine coverage is low, and your child is not vaccinated, it's quite likely that many of the people they come into contact with will not be vaccinated either. If one of these people contracts an infectious disease like measles, that person can transmit the disease to the other unvaccinated people they come in contact with, and cause the disease to spread very rapidly through the population.
Unlike vaccination, herd immunity does not give a high level of individual protection, and should not be regarded as a good alternative to getting vaccinated.
3
Some people in the community rely on herd immunity to protect them. Examples of such groups of people are particularly vulnerable to disease, and most likely cannot safely receive vaccines:
-
People without a fully-working immune system
-
People on chemotherapy treatment whose immune system is weakened
-
People with HIV
-
Newborn babies who are too young to be vaccinated
-
Elderly people
-
Patients who are very ill in the hospital
Overview:
Laboratory investigations 1 and 2 were adapted from the SEP and CDC website. Procedural steps and lab rules (coincides with my classroom lab. rules) were modified and made simple for students' engagement, understanding of concepts and having fun doing hands-on science.
With the on-going challenges presented in my science classes, the design and format of laboratory activities is constantly dictated by availability of equipment and materials and the make-up of my classes.
Objectives:
1. Describe the concept of herd community and why it is important.
-
Discuss reasons why some people are not immunized.
-
Calculate number and percentage of students in class need to be
immunized to prevent transmission of disease.
Materials:
Bag of colored jelly beans ( red, blue and green)
Brown paper lunch bag
Soft stuffed animal (small)
Red jelly bean will represent students with the communicable disease
Blue jelly bean will represent students unvaccinated
Green jelly bean will represent students being vaccinated
Procedure:
-
Place equal number of green and blue jelly beans in brown lunch bag with two red jellybeans. The total number of jelly beans in bag must total the number of students in the class. For example, in a class of 20 students, there should be two red jelly beans, nine blue jelly beans and 9 green jelly beans. Emphasize to students not to eat the jelly beans as they will be used again in the game.
-
Have each student randomly pick one jelly bean from the bag.
-
Tell all students with a red jelly bean to remain in their assigned seats while students with blue and green jelly beans should stand. Explain to students that when the teacher says, "strike" they will throw the stuffed animal at anyone who is standing (with a blue or green jelly bean).
-
Explain to students that vaccinated students with green jelly beans are protected and allowed to use their hands to deflect the stuffed animal to keep from getting hit with the stuffed animal. Unvaccinated students with blue jelly beans are not protected and must keep their hands to their side. Any unvaccinated student who gets hit must sit down. They are now sick and will be given a stuffed animal to throw at students standing. Vaccinated students who get hit should remain standing. Students will eventually noticed that those students who were not vaccinated will get hit with the stuffed animal and have to sit.
-
Establish the number of throws per student. Students will notice that the number of sick people begin to increase. Teacher may decide on the number of throws according to the severity of the disease. For example, a moderately contagious disease such as influenza could be represented by each sick student (having a red jelly bean) getting four throws whereas a highly contagious such as measles could be represented by each sick student getting ten throws.
-
Collect the colored jelly beans and reassign them. Again, tell the sick students to sit, while the well students remain standing. This time, all unvaccinated students will stand inside a barricade of vaccinated students.
-
The sick students will try to hit the unvaccinated students with the stuffed animal. Students will soon discover that they will have difficulty doing so because they are protected by students who are vaccinated. Explain to students that eventually a point will be reached when it would be virtually impossible for those students inside the circle (with blue jelly beans) to get hit with the stuffed animal. This point represents the threshold for herd immunity.