Pneumococcal Vaccines

Vaccination is a well-tolerated and effective option for preventing pneumococcal disease

Historically, vaccination has proven to be a safe, cost-effective option for dramatically reducing death and disability associated with many childhood diseases, such as measles and polio. Today, safe, well-tolerated pneumococcal conjugate vaccines exist that can save millions of young lives from pneumococcal-related death and disability.

How pneumococcal vaccines work

When a person's immune system first comes in contact with the pneumoccocal bacteria, it does not immediately recognize the threat, and is slow to mount a response. This response lag gives bacteria the chance to cause a life-threatening illness, especially in young children and the elderly. If a person is exposed to the same strain of pneumococcus a second time, the immune system immediately recognizes the threat and reacts swiftly to eliminate the bacteria, often before it can even cause illness.

When a person is vaccinated against pneumococcal disease, they are injected with small parts of killed bacteria, which create an “immune memory” for the bacteria. These killed bacteria cannotcause disease. Later, if the vaccinated individual encounters live pneumococcal bacteria, the immune system will recognize the bacteria and neutralize it so the person doesn’t get sick.

When a large proportion of a population receives a given vaccine (such as the pneumococcal vaccine), transmission of the disease to others is reduced. Unvaccinated individuals coming in contact with vaccinated individuals therefore have a lower chance of becoming infected with the organism. This phenomenon is called “herd immunity.”

Different vaccines target different types of pneumococcal bacteria. There are 90 types, or “serotypes” of pneumococcus. Many serotypes do not cause severe disease. An estimated 88% of global disease is caused by just 23 of the 90 serotypes. Eleven serotypes account for more than 80% of disease in children under age five. A vaccine’s “valency” refers to the number of bacterial serotypes it targets.

Some pneumococcal serotypes are particularly resistant to antibiotics. Giving antibiotics unnecessarily to treat a viral infection can contribute to the emergence of antibiotic resistance. This makes it harder and more costly to treat pneumococcal infections. That is why use of vaccines to prevent pneumococcal disease before it occurs is critically important.

Three main types of pneumococcal vaccines

1) Pneumococcal polysaccharide vaccine (PPV)

This vaccine is used in adults and immunocompromised children over age two years. It contains killed portions of sugars, or “polysaccharides” from 23 serotypes of pneumococcal bacteria.

2) Pneumococcal conjugate vaccine (PCV)
This vaccine is currently used in children under two years of age and is under development for use in adults. Children under age two have naïve immune systems, and they are unable to recognize the polysaccharide used in the PPV vaccine. The PCV vaccine contains the polysaccharide attached to, or “conjugated to” a more easily recognizable protein. The PCV effectively “tricks” the young immune system into recognizing the polysaccharide and providing protection against certain types of pneumococcus. These conjugated vaccines produce a stronger immune response and works more effectively than polysaccharide vaccines. However, the current PCV vaccines do not cover as many serotypes as the PPV vaccines because they are more complicated to develop and manufacture.

Pneumococcal conjugate vaccines have many advantages:

• Well-tolerated in young infants and adults
• Well-tolerated in people who are HIV-positive
• Can be administered with other vaccines, and on the same schedule as the diphtheria-tetanus-pertussis (DTP) vaccine
• Proven safe and effective in millions of children
• Can help control the growing problem of antibiotic-resistant pneumococcal disease
• May help protect others through herd immunity

The 7-valent PCV vaccine (PCV7) is in wide use around the world. It targets seven serotypes (4, 6B, 9V, 14, 18C, 19F, 23F). These serotypes are common causes of disease in the United States, Canada, Australia, and Europe, and PCV7 has been highly effective at reducing pneumococcal disease in these countries.

However, different serotypes of pneumococcus have different global distributions. While many of the seven serotypes included in the PCV7 vaccine are common worldwide, additional serotypes are also common in developing countries and must be included to maximize the effect of the vaccine in these countries. Serotypes 1 and 5, for example, cause a much greater proportion of disease in developing countries than they do in developed countries. Serotypes 3, 7F, and 19A are also important serotypes of global disease burden.

Universal use of the PCV7 vaccine would prevent substantial morbidity and mortality in the developing world. Expanded valency vaccines, however, would prevent an even larger proportion of disease globally, especially in the developing world. A 10-valent vaccine manufactured by GlaxoSmithKline is currently marketed in Europe and other developed countries, and is expected to be prequalified in 2009. It is expected to be able to prevent 66-88% of pediatric pneumococcal disease. A 13-valent vaccine manufactured by Wyeth, which would prevent an estimated 73-92% of pneumococcal disease among children, is also in the advanced stages of development. Additional research is ongoing to produce other conjugate vaccines. None, however, have entered into development phase and experts estimate that the earliest they will be available is 2015.

3) Protein vaccines

Much of the current research to develop novel pneumococcal vaccines is centered on finding proteins that are common to most strains of pneumococcus. These “common proteins” could protect against many types of pneumococcus in a single, protein-based vaccine.