GCSE · Biology · Edexcel · Spec 1BI0

Advantages, disadvantages and herd immunity

Imagine a classmate who can't have a vaccine because they're allergic to an ingredient. What decides whether the disease ever reaches them? Not their jab.

Biology · Weigh it up

Do the benefits of vaccination outweigh the risks?

The claim

The benefits of vaccination outweigh its risks.

Place each piece of evidence to load the balance. Mark the strong ones — they count double.

A vaccinated person has long-term immunity, so they are less likely to contract the disease or become ill, and less likely to need treatment for it.
Evidence 1: does it support or challenge the claim?SupportsChallenges
Strong evidence
Smallpox killed around 30% of those infected and could leave survivors with scarring and blindness. Vaccination eradicated it, and the WHO announced that in 1980.
Evidence 2: does it support or challenge the claim?SupportsChallenges
Strong evidence
When a high proportion of a population is vaccinated, the spread of the pathogen is reduced, so people who cannot be vaccinated may be protected too.
Evidence 3: does it support or challenge the claim?SupportsChallenges
Strong evidence
A vaccine is trialled in the laboratory, then on animals, then on humans, and approved only when the evidence shows the benefits outweigh the risks.
Evidence 4: does it support or challenge the claim?SupportsChallenges
Strong evidence
Short-term side effects: aching muscles, a fever, or an arm that hurts where the vaccination was given.
Evidence 5: does it support or challenge the claim?SupportsChallenges
Strong evidence
Very rarely, there are more severe side effects, such as an allergic reaction.
Evidence 6: does it support or challenge the claim?SupportsChallenges
Strong evidence

Same pathogen, two towns

Few people vaccinatedvsA high proportion vaccinated

Only one thing differs between the towns: how many people are vaccinated.

Focus

Spread from person to person

Few people vaccinated

The pathogen can spread easily.

A high proportion vaccinated

The spread of the pathogen is reduced.

The insight

Vaccinated people are less likely to contract the disease, so there are fewer people to pass it on.

Can it reach someone who cannot be vaccinated?

Few people vaccinated

Yes, quite easily: nothing is slowing it down.

A high proportion vaccinated

It is prevented from reaching them.

What that means for them

Few people vaccinated

They are exposed to the pathogen.

A high proportion vaccinated

They may be protected.

What we call it

Few people vaccinated

No herd immunity.

A high proportion vaccinated

Herd immunity.

Biology · How many is enough?

Measles and the herd immunity threshold

Measles is a communicable viral disease spread by droplets from coughs and sneezes. What percentage of the population needs to be vaccinated for herd immunity to measles?

Your estimate

50%

Measles is a communicable viral disease spread by droplets from coughs and sneezes. What percentage of the population needs to be vaccinated for herd immunity to measles? Estimate between 0% and 100%.

0%100%

Measles · how herd immunity was lost

Reason it through

Why were there further measles outbreaks in England after MMR had brought measles down to very low levels?

Link 1 of 4

First link · your turn

What happened in 1998?

Locked — reveal the link above first

Biology · Which idea is yours?

Three things people say about vaccines

A group chat is arguing about a vaccine.

Which is closest to what you think right now?

A brand-new vaccine must be riskier than everyday things like travelling in a car, so skipping it is the safe choice.The MMR vaccine causes autism.If most people are vaccinated, someone who can't be vaccinated is definitely safe.Vaccines do carry small risks, but the disease is the bigger risk, and new things just feel scarier than they are.

How sure are you?

I'm sureI think soI'm guessing

A brand-new vaccine must be riskier than everyday things like travelling in a car, so skipping it is the safe choice.

This is a common misconception

People tend to underestimate the risks of familiar activities, like travelling in a car, and overestimate the risks of unfamiliar things, like new vaccines. The risks of vaccination are very low, and a vaccine is only approved when the evidence shows its benefits outweigh its risks. The risk from the disease is much higher than the risk from the vaccine.

The MMR vaccine causes autism.

This is a common misconception

That idea came from a fundamentally flawed 1998 study that used a very small number of individuals. It has been discredited, and other studies found no link between the MMR vaccine and autism. The scare did real damage: MMR rates dropped and herd immunity to measles was lost.

If most people are vaccinated, someone who can't be vaccinated is definitely safe.

This is a common misconception

Close, but too strong. A high proportion vaccinated reduces the spread of the pathogen, so people who cannot be vaccinated may be protected. 'May' matters: it lowers their chance of meeting the pathogen, it is not a guarantee. In the same way, a vaccinated person is 'less likely' to contract the disease, not guaranteed to avoid it.

Vaccines do carry small risks, but the disease is the bigger risk, and new things just feel scarier than they are.

This matches the evidence

Yes. Vaccination is not risk-free, but its risks are very low, and people tend to overestimate unfamiliar risks.

Check the claim against the evidence, not against how familiar it feels.

Edexcel Biology · Write it, then mark it

Explain it in your own words

A school nurse says: 'Vaccinating most of the town also helps the people who can't have the vaccine.' Explain how vaccinating a high proportion of a population can protect people who cannot be vaccinated. [3 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Most people are vaccinated, so they are less likely to contract the disease. (1 mark)
So the spread of the pathogen from person to person is reduced. (1 mark)
So the pathogen is prevented from reaching people who cannot be vaccinated, who may be protected (herd immunity). (1 mark)

Model answer

If a high proportion of the population is vaccinated, most people are less likely to contract the disease. That reduces the spread of the pathogen from person to person. So it is prevented from reaching people who cannot be vaccinated, and they may be protected. This is herd immunity.

Chain it: more vaccinated, less spread, fewer chances to reach the unvaccinated, so they may be protected.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

A jab protects you. Can it protect people who can't have one?

What you need to know

Vaccination has a large positive effect on public health by controlling the spread of communicable diseases.
A vaccinated person is less likely to contract the disease or become ill, and less likely to need treatment.
Have a goYour mate Jo has had the jab and announces, 'So I can NEVER catch it now.' Using what you just read, fix Jo's sentence.
A vaccinated person is less likely to contract the disease or become ill.
'Less likely' is the claim; 'never' turns a lower chance into a guarantee.
Smallpox killed around 30% of those infected, and vaccination eradicated it. The WHO announced that in 1980.
Vaccination is not risk-free: short-term side effects like aching muscles or fever, and very rarely a severe one such as an allergic reaction.
Vaccines are trialled in the laboratory, then on animals, then on humans, and approved only if the benefits outweigh the risks.
People tend to overestimate the risks of unfamiliar things like new vaccines, and underestimate familiar ones like travelling in a car.
Have a goWhich do people tend to overestimate the risk of: a car journey, or a brand-new vaccine?
The brand-new vaccine.
Unfamiliar things feel riskier than they are, even though the risks of vaccination are very low.
Some people cannot be vaccinated, for example if they are allergic to an ingredient or have a severely weakened immune system.
With a high proportion vaccinated, the spread of a pathogen is reduced, so people who cannot be vaccinated may be protected: herd immunity.
Have a goPathogen A is loose in a town where hardly anyone is vaccinated. Pathogen B is loose where most people are. Which one reaches a person who can't be vaccinated more easily?
Pathogen A, in the town where hardly anyone is vaccinated.
With few people vaccinated the pathogen spreads easily; a high proportion vaccinated reduces its spread.
For measles, around 95% of the population needs to be vaccinated for herd immunity.
A fundamentally flawed 1998 study, since discredited, was followed by falling MMR rates, lost herd immunity and measles outbreaks in England.

The big picture

Vaccination protects the person vaccinated and can eradicate a disease. It has short-term side effects and, very rarely, severe ones. When a high proportion of a population is vaccinated, herd immunity may protect people who cannot be vaccinated, and the measles story shows that protection can be lost.

Key points

1Vaccination controls the spread of communicable diseases, and a vaccinated person is less likely to contract the disease or become ill.

2Vaccination is not risk-free (short-term side effects, very rarely severe ones), but vaccines are approved only when the benefits outweigh the risks.

3A high proportion vaccinated reduces spread, so people who cannot be vaccinated may be protected: that is herd immunity.

4Around 95% must be vaccinated for herd immunity to measles, and the discredited 1998 study shows how fast it can be lost.

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Worked example

Problem

A classmate says: 'Vaccines have side effects, so they're not worth it.' Write a two-sentence reply that weighs one benefit against one risk. Show how you decide what goes in.

⚠ Watch out

Writing that a vaccinated person can't catch the disease, or that herd immunity makes unvaccinated people safe. The accurate wording is that they are 'less likely' to contract it, and unvaccinated people 'may be protected'.

🧠

Memory hook

Me first, then we: my jab lowers MY chance of the disease, and enough of US vaccinated may shield the people who can't have one.

✓

Check yourself

Someone who cannot be vaccinated lives in a town where a high proportion of people are vaccinated. Why might they be protected, and why is 'may' the right word?

Flashcards

(13)

What effect does vaccination have on public health?

A large positive effect: it controls the spread of communicable diseases.

How does being vaccinated help the person who has the vaccine?

They have long-term immunity, so they are less likely to contract the disease or become ill, and less likely to need treatment.

What did smallpox do, and what happened to it?

It killed around 30% of those infected and could leave survivors with scarring and blindness. Vaccination eradicated it; the WHO announced this in 1980.

What are the risks of vaccination?

It is not risk-free. Short-term side effects such as aching muscles or fever, and very rarely more severe ones such as an allergic reaction.

When is a vaccine approved for use?

Only when the evidence shows the benefits outweigh the risks, after laboratory, then animal, then human testing.

What mistake do people tend to make when judging risk?

They underestimate familiar risks (like travelling in a car) and overestimate unfamiliar ones (like new vaccines), even though vaccination risks are very low.

Who cannot be vaccinated?

For example people allergic to the vaccine's ingredients, or with a severely weakened immune system (such as some people living with cancer or HIV). Some people also choose not to be.

Explain herd immunity.

A high proportion of the population is vaccinated, so the spread of the pathogen is reduced and it is prevented from reaching people who cannot be vaccinated, who may be protected.

What happens if none or only a small proportion of a population is vaccinated?

A pathogen can spread easily from person to person.

What proportion needs to be vaccinated for herd immunity to measles?

Around 95% of the population.

Which diseases does the MMR vaccine protect against?

Measles, mumps and rubella. Once MMR was introduced, measles cases fell rapidly to very low levels.

What was wrong with the 1998 study linking MMR to autism?

It was fundamentally flawed, using a very small number of individuals, and has been discredited. Other studies found no link.

What followed the wide newspaper publicity for that study?

MMR vaccination rates dropped, herd immunity to measles was lost, and there were further measles outbreaks in England.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Do the benefits of vaccination outweigh the risks?

Measles and the herd immunity threshold

Three things people say about vaccines

Explain it in your own words

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