Final answer:
The priority groups for the pneumonia vaccine are children younger than 2 years and adults older than 65 years, who are more vulnerable to pneumococcal infections.
Step-by-step explanation:
The priority groups for the pneumonia vaccine are children younger than 2 years and adults older than 65 years. These populations are considered the most vulnerable to pneumococcal infections. Children are more susceptible to infections due to their developing immune system, while older adults have a weakened immune response.