This problem is not in the NEET syllabus, but A-Level and IB ask it…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
This problem is not in the NEET syllabus, but A-Level and IB ask it. A disease has . A town has people, and nobody is immune now. A vaccine protects of the people who get it.
- What share of the town must be immune to stop the spread?
- What share must be vaccinated, if the vaccine protects of those who receive it?
- How many people must be vaccinated?
Need a reminder? The key ideaShow
After a second meeting with an antigen, the response is quicker and stronger because of memory cells. An antibody has two heavy and two light chains, HL, and two antigen-binding sites. In active immunity the body makes its own antibodies. In passive immunity the antibodies are given ready made. Herd immunity needs a share of at least of the population to be immune.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. . Town: people. Vaccine: effective.
Plan. Find the share that must be immune. Then allow for the vaccine that does not always work.
Step 1. The share immune. , which is .
Step 2. The share to vaccinate. , which is .
Step 3. The people. people.
Answer: ; ; people.
Check. of is , and .
Watch out. The simple formula assumes that people mix at random and that the vaccine is the only protection. Real towns are more complex.
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