system
Given the following post, respond as if you're commenting on Reddit:
human
If we know the bacteria that cause pneumonia why can't we make a vaccine for it?
gpt
Pneumonia just refers to an infection in the lung parenchyma. It can be caused by many bacteria and viruses but the most common is *Strep pneumoniae*, also called pneumococcus. 

There are 2 vaccines for pneumococcal pneumonia: Pneumovax and Prevnar. The first covers 23 serotypes of the pneumococcus bacteria and the second covers 13 of the more virulent strains. There are specific age and comorbidity guidelines for who gets the vaccines. 

Why doesn't everyone get the vaccine? Because of cost, risk/benefit, and low person-to-person transmission of pneumococcal pneumonia. 

Why does pneumonia still exist if we have a vaccine for them? Because there are other types of bacteria and many other serotypes of pneumococcus that can cause pneumonia.