Which of the following statements is true? 1. The first vaccine was developed for cowpox. 2. Missed immunizations cannot be given at future doctor visits. 3. Travelers to other countries are often required to get special vaccinations. 4. Before Jenner's vaccine, there was no prevention for smallpox.

3

Explanation:

Vaccines protect travelers from serious diseases. Depending on where you travel, you may come into contact with diseases that are rare in the United States, like yellow fever. Some vaccines may also be required for you to travel to certain places.

a problem could be dealing witj emotional stress..all of these factors contribute to emotional stress.