15-30 minutes making copies and preparing cards
of the Two-Day Disease – Teacher Protocol Sheet (make 1 copy)
Outbreak at Western High and A Little Sleuthing (make
1 copy per student) – These are on the
same page; you will need to cut them apart.
Following an Epidemic (make 2 copies per student and
Red, pink, and black cards (make 1 of each per student)
Folded pieces of paper labeled “immune” and “susceptible” (make
enough of each for half the students)
activity introduces students to modeling as a scientific
exercise. Students learn how models based on observations
of disease transmission can be used to predict the
likelihood of epidemics and to help public health officers
recommend policies to protect the public from infectious
diseases. Students use an in-class simulation to explore
how infectious diseases spread through a population
and discover the phenomenon of herd immunity.
will be able:
Explain how immunizing a significant proportion of
a population against a disease prevents epidemics of
that disease (herd immunity).
2. Be able to list factors that affect the proportion
of a population that must be immunized to prevent epidemics.
3. Understand how large-scale vaccination programs
help control infectious diseases.
Science Education Standard:
Standard A – Science as Inquiry
USE TECHNOLOGY AND MATHEMATICS
TO IMPROVE INVESTIGATIONS AND COMMUNICATIONS.
of technologies, such as hand tools, measuring
instruments, and calculators, should be
an integral component of scientific investigations.
The use of computers for the collection,
analysis, and display of data is also a
part of this standard. Mathematics plays
an essential role in all aspects of an
inquiry. For example, measurement is used
for posing questions, formulas are used
for developing explanations, and charts
and graphs are used for communicating results.
Content Standard F- Science in Personal
and Social Perspectives
PERSONAL AND COMMUNITY HEALTH
The severity of disease symptoms is dependent
on many factors, such as human resistance
and the virulence of the disease-producing
organism. Many diseases can be prevented,
controlled, or cured. Some diseases, such
as cancer, result from specific body dysfunctions
and cannot be transmitted.
AND TECHNOLOGY IN LOCAL, NATIONAL, AND GLOBAL CHALLENGES
Individuals and society must decide on proposals
involving new research and the introduction of new technologies
into society. Decisions involve assessment of alternatives,
risks, costs, and benefits and consideration of who benefits
and who suffers, who pays and gains, and what the risks
are and who bears them. Students should understand the
appropriateness and value of basic questions--"What
can happen?"--"What are the odds?"--and "How
do scientists and engineers know what will happen?"
Standard G – History and Nature of Science
NATURE OF SCIENTIFIC KNOWLEDGE
Because all scientific ideas depend on experimental and
observational confirmation, all scientific knowledge
is, in principle, subject to change as new evidence becomes
available. The core ideas of science such as the conservation
of energy or the laws of motion have been subjected to
a wide variety of confirmations and are therefore unlikely
to change in the areas in which they have been tested.
In areas where data or understanding are incomplete,
such as the details of human evolution or questions surrounding
global warming, new data may well lead to changes in
current ideas or resolve current conflicts. In situations
where information is still fragmentary, it is normal
for scientific ideas to be incomplete, but this is also
where the opportunity for making advances may be greatest.
The re-emergence of some diseases can be explained by
the failure to immunize enough individuals, which
results in a greater proportion of susceptible individuals
in a population and an increased reservoir of the
infectious agent. Increases in the number of individuals
with compromised immune systems (due to the stress
of famine, war, crowding, or disease) also explain
increases in the incidence of emerging and re-emerging
Global vaccination strategies are a cost-effective means
of controlling many infectious diseases. Because immunized
people do not develop diseases that must be treated with
antimicrobial drugs, opportunities for pathogens to evolve
and disseminate drug resistance genes are reduced. Thus,
mass immunization reduces the need to develop newer and
more expensive drugs.
As long as a disease remains endemic in some parts of
the world, however, vaccination programs must be maintained
everywhere, because an infected individual can travel
anywhere in the world within 24 hours. Once global vaccination
programs eliminate the infectious agent, (as in the case
of the smallpox virus), vaccination is no longer necessary
and the expense of those programs is also eliminated.
It is estimated that the United States has saved $17
billion so far as a result of the eradication of smallpox
(which cost, according to the World Health Organization,
$313 million across a 10-year period).
in vaccination programs explain the re-emergence of
infectious diseases. For example, the diphtheria
outbreak in Russia in the early 1990s may have been due
to lapses in vaccination programs associated with the
breakup of the Soviet Union. Inadequate vaccines and
failure to obtain required “booster shots” also
explain some disease re-emergence. The dramatic increase
in measles cases in the United States during 1989–1991
was likely caused by failure to give a second dose of
the vaccine to school-age children. The American Academy
of Pediatrics now recommends that all children receive
a second dose of the measles vaccine at either ages 4–6
The activity, Superbugs and Antibiotic Resistance, provide
explanations for the re-emergence of some infectious
diseases. This activity introduces students to the idea
that the re-emergence of some infectious diseases can
be explained by a failure to immunize a sufficient proportion
of the population. Students learn that epidemics can
be prevented by immunizing part of the population, leading
to herd immunity.
Prerequisite Student Knowledge
should be familiar with how immunization protects individuals
from infectious diseases.
You will need to prepare the following materials before
conducting this activity:
Outbreak at Western High (make 1 copy per student)
- A Little Sleuthing (make 1 copy per student)
- Following an Epidemic (make 2 copies per student
and 2 transparencies)
pink, and black cards (make 1
of each per student)
- Folded pieces of paper labeled “immune” and “susceptible” (make
enough of each for half the students)
1. Introduce the activity by distributing one copy
of Measles Outbreak at Western High, to each student
and asking the students to read it.
The scenario described on Measles Outbreak is fictitious,
but is based on an outbreak of measles that occurred
in Washington State in 1996. An alternate way to
introduce the activity is to assign students to make
a list of the childhood diseases that they, their
parents (or someone from their parents’ generation),
and their grandparents (or someone from their grandparents’ generation)
had. Explain that “childhood diseases” means
diseases that people usually have just once and do
not get again (for example, chicken pox). Explain
that you do not mean diseases like the flu, strep
throat, or colds. On the day you wish to begin the
activity, ask students to name some of these diseases,
and then ask them to count the number of different
diseases each generation in their family had them.
Total these numbers across all of the students in
the class and ask students to suggest why (in general)
their parents and grandparents had more diseases
than they did. Students likely will suggest (correctly)
that vaccinations against many diseases are now available.
2. After students have read Measles Outbreak, ask
them to speculate about what might have happened
to cause a sudden outbreak of a disease such as measles
that normally, today, is relatively rare in the United
Students likely will know that most children in the
United States today are vaccinated against measles.
They may speculate that the students at Western High
were not vaccinated, or that the vaccines did not
work in their cases, or even that the pathogen causing
this form of measles was somehow able to evade the
immune defenses that had been triggered by the vaccinations
these children received.
3. Distribute one copy of Master 4.2, A Little Sleuthing,
to each student and ask the students to read the
story and think about the question that ends it.
4. Point out that despite the success of the measles
vaccine, there continues to be small outbreaks of
measles in the United States. Explain that the key
to understanding why this is true and to answering
the question that ends the story about Western High
lies in understanding how disease spreads in a population.
5. Explain to students that to help them
understand how disease spreads in a population, they
in a simulation of the spread of a fictitious disease
you will call the “two-day disease.” Distribute
two copies of Master 4.3, Following an Epidemic,
to each student and display a transparency of this
master. Then, direct students to perform two simulations
of the spread of the two-day disease, according to
the instructions provided on page 77, immediately
following the activity.
An “epidemic” is typically defined as “more
cases of a disease than is expected for that disease.” Although
this is not a very specific definition, it does make
it clear that whether scientists call an outbreak
of a disease an epidemic depends on the specific
disease involved. Though there is no distinct line
between an “outbreak” and an “epidemic,” epidemics
are generally considered to be larger in scale and
longer lasting than outbreaks. Today, five cases
of measles within a population could be considered
an epidemic because no cases are expected. For this
simulation, assume that an epidemic is in progress
if 25 percent or more of the population is sick at
one time. Observations that students might make about
the table and graph that result from the first simulation
- an epidemic occurred because a large portion of
the class was sick at the same time;
- at the beginning of the epidemic, only a few
people were sick on the same day; in the
middle of the epidemic,
a lot of people were sick at the same time;
and at the end, only a few people were
- by the end of the simulation, everyone
was immune; and
- once it started, the disease spread rapidly.
Observations that students might make
about the table and graph that result
- only a few people were sick on any one day;
- no epidemic occurred;
- at the end of the simulation, some people were
still susceptible; and
- some people in the population
never got sick.
from the field test: Do a practice
of the simulation
before you do the runs in
which you collect
will allow you to
address any confusion students
the simulation and will make subsequent runs go much faster.
If you have time, you may want to repeat the simulation,
in particular the
second simulation in which
half of the class
In order for students
to observe herd immunity,
the population should
not get sick.
on the arrangement
of immune and susceptible
in the class (which
this may not happen
the first time you
run this simulation.
the activity by asking, “Why
did an epidemic occur in the first population, but not
in the second?” and “Why didn’t all
of the susceptible people in the second population get
sick?” Introduce the term “herd immunity” and
describe it as a phenomenon that occurs when most of
the people in a population are immune to an infectious
disease. Susceptible people in the population are protected
from that disease because the infectious agent cannot
be effectively transmitted.
Allow students to discuss their responses to the two
questions before you introduce the term herd immunity.
Students will likely make comments such as, “Everyone
sitting near John was immune, so the disease just died
out.” At that point, you can respond by saying, “Yes,
what you have just explained is what epidemiologists
call herd immunity.” Then you can provide a more
2. Ask students to explain, based on their experience
in the disease transmission simulation, what would happen
if measles vaccinations dropped to a low level in a population.
Students should be able to explain that there would be
many susceptible people in the population, so the disease
would be transmitted from one to another without dying
out. A measles outbreak or epidemic would occur. If students
do not mention “re-emergence,” emphasize
this point by saying, “Yes, measles would re-emerge
in the population.”
Remind students about the measles outbreak
story. Ask them to write a final paragraph to the story in
which they use the term herd immunity to answer the following
didn’t the unvaccinated or inadequately
vaccinated students and teacher at Western High
get measles when they
were children rather than as teenagers or adults?
Students should be able to explain that the unvaccinated
or inadequately vaccinated students at Western High were
protected by herd immunity when they were younger: Because
most of the people around them were immune, the infectious
agent could not be transmitted from those people.
- Why is vaccination not only a personal health issue,
but also a public health issue?
Vaccination is a public health issue because maintaining
high levels of immunity in a population prevents
epidemics and protects the small percentage of
susceptible people from
students are discussing their findings, listen to see
if students can answer the following questions:
- Can they explain how immunizing a significant proportion
of a population against a disease prevents epidemics
of that disease (herd immunity)?
- Can they list factors that affect the proportion
of a population that must be immunized to prevent
- Can they explain how large-scale vaccination
programs help control infectious diseases?