Year 9 Science · Unit 1 · Lesson 10
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank to complete each sentence. Two words will not be used.
When a large enough proportion of a population is , a disease cannot spread widely. This protection is called and it shields people who are unable to be vaccinated themselves.
The minimum proportion of people who must be immune is called the herd immunity . This number depends on the basic reproduction number, written as , which measures how many people one infected person passes the disease on to.
When herd immunity breaks down, outbreaks often begin in a of unvaccinated people living close together. A person who chooses not to vaccinate but still benefits from others' immunity is called a .
True or False? Fix the false ones
Circle T or F for each statement. If the statement is false, rewrite it correctly on the line below.
Herd immunity means that every single person in the community is immune to the disease.
Correct it:
The higher the R₀ of a disease, the lower the herd immunity threshold needed to protect the community.
Correct it:
Babies too young to receive vaccines can still be protected by herd immunity if enough people around them are vaccinated.
Correct it:
Measles has an R₀ of about 15, which means it requires a herd immunity threshold of approximately 93%.
Correct it:
1. Name two groups of people who cannot be vaccinated and therefore rely on herd immunity for protection.
2. In 2019, a measles outbreak in Samoa killed 83 people. Vaccination coverage had dropped to about 31%. Using the concept of herd immunity, explain why this outbreak happened.
Wrap Up
In one sentence, what was the main idea of this lesson?