1955: The Polio Announcement Families Had Waited For
A vaccine needed more than a promising idea. A huge trial helped turn hope into evidence.
Estimated CEFR reading level: B1. A chronological explanation separates vaccine development, a trial and the announcement of its results. This is an editorial estimate, not an official certification.
Five useful words
British English pronunciation (IPA). Audio uses an available English voice on your device.
vaccine /ˈvæksiːn/
nounA preparation used to help the body develop protection against a disease.
The team developed a vaccine.
trial /ˈtraɪəl/
nounAn organised test used to find out whether something works.
Children participated in a large trial.
participate /pɑːˈtɪsɪpeɪt/
verbTo take part in an activity.
Many families agreed to participate.
evidence /ˈevɪdəns/
nounInformation that helps show whether something is true.
The trial produced evidence about protection.
evaluation /ɪˌvæljuˈeɪʃən/
nounA careful assessment of something.
Francis led the evaluation of the vaccine.
The story
On 12 April 1955, scientists and reporters gathered at the University of Michigan. They were waiting for important news about a vaccine developed by Jonas Salk and his team. Could it protect children against paralytic polio, a disease that could stop people moving parts of their bodies?
Thomas Francis Jr. announced the results of a large field trial. More than 1.8 million children had participated. Participation did not mean that every child received the vaccine: researchers needed comparison groups to judge its effect.
The results showed that the vaccine could prevent many cases of paralytic polio. For families worried about the disease, the announcement brought strong hope.
The date marks the announcement of evidence, rather than the first day anyone had thought about vaccination. Salk's team developed the vaccine, while Francis led its evaluation. The story shows why testing and teamwork matter alongside a famous inventor's name.
Three questions
Try answering before you open the answer. You can use your own words.
- What was announced on 12 April 1955?
Show answer
The results of the large trial of the Salk polio vaccine.
- Did every participating child receive the vaccine?
Show answer
No. The trial also needed comparison groups.
- How did Salk's and Francis's roles differ?
Show answer
Salk and his team developed the vaccine; Francis led its evaluation.
Let's talk about it
A few ideas to chat about - pick any that interest you.
- What helps you understand a science announcement?
- Do you usually notice the team behind a famous discovery?
- Would a museum display about a medical trial interest you?
- What kind of evidence makes a new invention sound convincing to you?
- Which scientific achievement would you like to learn more about?
Practise a useful pattern
Use while to compare the two scientists' roles. Write one sentence about Salk and Francis.
Example: Salk's team developed the vaccine, while Francis led its evaluation.
Frequently asked questions
Who announced the 1955 polio trial results?
Thomas Francis Jr. announced them at the University of Michigan on 12 April 1955.
Were all 1.8 million participating children vaccinated?
No. Participation included comparison groups as well as children who received the vaccine.
Sources and editorial notes
Original learning article by Poly-Puff, written from the factual sources below. Sources checked on 17 October 2026. The artwork and learning activities were created for this article.
The University of Michigan record, including the original release, was read directly. Its participation total includes different trial groups; it is not a count of vaccine doses or proof that every participant received the vaccine. The Salk Institute supports the development history. This is a historical learning story, not present-day medical guidance.
