Since the pneumococcus bacterium causes so many common infections in children and adults, scientists have long been laboring to come up with a vaccine against this bug. As a result of this prolonged effort at inventing a vaccine against pneumococcus, there are two types of pneumococcal vaccine today. The first type is called the pneumococcal polysaccharide vaccine, and the second type is called the pneumococcal conjugate vaccine.

The polysaccharide vaccine first became available in 1979, and it is only recommended for individuals whose immune system is weakened. The polysaccharide vaccine was not given to babies because this vaccine does not work for children less than two years old. Because the immune system for children younger than two years is still immature, the polysaccharide vaccine does not trigger the immune response necessary for this vaccine to work.

Due to this shortcoming, another pneumococcal vaccine was developed. In 2000, a new type of pneumococcal vaccine, called the conjugate pneumococcal vaccine, became available. The conjugate vaccine is made differently than the polysaccharide vaccine, and the conjugate vaccine works well to protect even young babies.

The polysaccharide pneumococcal vaccine is sometimes known as the “pneumonia” vaccine, because it helps to prevent pneumonia caused by the pneumococcus bacterium. This is a vaccine that is recommended universally for individuals older than sixty-five years and for people with a weak immune system. People with chronic heart, lung, kidney, or liver diseases have a weakened immune system, and they are candidates for the polysaccharide vaccine. In addition, people with diabetes, HIV, cancer, or sickle cell disease should get this vaccine as well. Finally, people without a working spleen should receive this vaccine because the spleen plays an important role in fighting off infection caused by certain types of bacteria, including the pneumococcus bacterium.

On the other hand, the pneumococcal conjugate vaccine is quite similar to the Hib vaccine because they are both recommended for all babies, and they work well in infants younger than two years. Babies who have a problem with their immune system may need to get both the polysaccharide vaccine and the conjugate vaccine. The conjugate vaccine is given first, because the polysaccharide vaccine does not work for children until they are older than two years.

One of the initial concerns about the use of pneumococcal vaccine was that the vaccine could encourage other types of pneumococcus bacterium that are not covered by the vaccine to flourish. Since both types of vaccines only cover a fraction of the total number of types of pneumococci bacteria, doctors have found that other types of pneumococcus bacterium that are not protected by the vaccine are increasingly causing more serious infections. In other words, since the vaccine is designed to target certain types of pneumococcus, other types are taking on the role of triggering infections.

This changing trend means that sooner or later, the usefulness of the pneumococcal vaccines would decrease unless the composition of the vaccine is altered to follow a moving target.

So far, the current pneumococcal vaccine still works quite well for the existing strains of the pneumococcus bacterium. When other strains of pneumococcus not covered by the vaccine start to cause more infections, the vaccines will need to be modified to accommodate the shifting demographics of the pneumococcus bacterium.