In an experiment to test the effectiveness of a new vaccine, 50 rats received an injection of equal doses of the vaccine and 50 other rats received an injection of equal doses of a weak salt solution. Two months later, all of the rats received injections that contained equal doses of live, disease-causing organisms. The experimental results are shown in the chart below:
Effectiveness of New Vaccine
Injection: 50 Rats Received
Number of Rats That Developed the Disease
Number of Rats That Did Not Develop the Disease
Vaccine
7
43
Weak Salt Solution
48
2

Based on the experiment in Task 3, propose two suggestions that could improve the results of this experiment. Explain how these suggestions could help to better verify if the vaccine is ready for human testing.