A measles outbreak

 A viral infection

◦ Initial symptoms: fever,

malaise, lack of appetite

◦ Rash appears about 14

days after infection.

 Spread through air

◦ Droplets can remain in

air for up to 2 hours

 The incubation period

is 10-12 days. What

does this mean?

 Jackie (a 1st grader) and her family recently

returned from a family vacation to the

Philippines.

 A few days after her return to school, she got

a fever, coughing, and a runny nose.

 A few days after that, she developed a rash.

 You are in her class and have been exposed.

There are two 1st grades and they interact

continuously throughout the day. There are

40 students total between the two 1st grades.

 How protective the vaccine was for people in

your class?

 Vaccine effectiveness is a proportion, more

specifically, the proportionate reduction in

the number of cases for those who were

vaccinated.

Vaccine effectiveness =

Excess risk

Risk among unvaccinated group

 Excess risk = Risk among unvaccinated – Risk

among those vaccinated

 How protective the vaccine was for people in

your class?

½ of the children were vaccinated; ½ were not

Of those vaccinated, one became ill; of those

not vaccinated, 18 became ill

 Calculate the incidence rate of measles for

those who were vaccinated.

 Calculate the incidence rate of measles for

those who were not vaccinated.

Vaccine

status

Total Ill Well Incidence

rate %

Vaccinated 20

Not

vaccinated

20

For this example....

(incidence rate in NV – incidence rate in V)

Incidence rate in NV