Pneumococcus: The Disease & Vaccines

Pneumococcus: The Disease & Vaccines

Pneumococcal bacteria affect the most vulnerable people in a population, including infants, toddlers and the elderly. An infected person can have different symptoms depending on the location of the infection:

  • Meningitis, an inflammation of the lining of the brain and spinal cord
  • Sepsis, a bloodstream infection
  • Pneumonia, an infection of the lungs
  • Otitis media, an ear infection
  • Pericarditis, an infection of the lining of the heart
  • Septic arthritis, an infection of the fluid in joints

Because many elderly people get pneumonia, the vaccine to protect against pneumococcus is often called the “pneumonia vaccine.” When the vaccine was first routinely recommended for babies, some parents became aware of it as “the vaccine that protects against ear infections” because of its impact on one of the more familiar problems in young children. 

The first pneumococcal vaccine was introduced for adults in 1977, but it didn’t work well in infants. The vaccine didn’t work in children less than 2 years of age for the same reason that they are at greatest risk of serious infection from pneumococcal bacteria — they are unable to develop immunity to the sugar coating of the bacteria, called a polysaccharide. So, every year, pneumococcus continued to cause millions of infections in children that led to:

  • 5 million ear infections
  • 40,000-50,000 hospitalizations for pneumonia
  • 17,000 cases of bloodstream infections
  • 700 cases of meningitis
  • 200 deaths 

Finally, in 2000, a second type of pneumococcal vaccine became available. Because it protected young children, it was recommended for all infants and young children in the U.S.

An ounce of prevention is worth a pound of cure

When it was discovered that antibiotics could treat bacterial infections, interest in developing a vaccine against pneumococcus decreased. The thinking was, “why prevent something that we can easily treat?” Unfortunately, that approach quickly showed why prevention is better than treatment. 

In the 1940s the different types of pneumococcal bacteria could all be treated with the antibiotic, penicillin. But, over time, many types changed so that they would not be killed with antibiotics. This evolution is called “antibiotic resistance.”  Several types evolved to resist not only penicillin but other antibiotics as well.  As a result, treatment options became increasingly limited.

Some types of pneumococcal bacteria are now highly resistant to most antibiotics. Our reliance on and overuse of antibiotics led to these changes, backing us into a corner when treating infections caused not only by pneumococcus but also by other types of bacteria as well. Antibiotic resistance causes almost 3 million infections and 35,000 deaths in the U.S. each year. These deaths occur because we have no tools to treat the bacteria causing the infections. This experience has shown us why prevention is so important.

The disease

What is pneumococcus?

Pneumococcus is caused by a bacterium called Streptococcus pneumoniae. The most common pneumococcal infection that causes hospitalization is pneumonia. Children with pneumonia develop: 

  • High fever
  • Cough
  • Rapid, difficult breathing 

Sometimes the bacteria cause pus to accumulate not only inside the lung but also between the lung and the chest wall. This condition is called empyema. Pressure from the accumulated pus can cause the lung to compress and collapse. Although most children with pneumococcal pneumonia recover, the disease can sometimes be fatal.

How do you catch pneumococcus?

Pneumococcal bacteria commonly line the inside surface of the nose and the back of the throat. About 25 of every 100 people have these bacteria living there. They can spread the bacteria to others, including young children, who usually encounter the bacteria sometime in the first two years of life. Because most adults are immune to pneumococcus, a baby will get antibodies from their mother before birth (i.e., maternal antibodies). These antibodies protect the baby for a few months after birth, but as they decrease, the baby becomes vulnerable to pneumococcus. Most children don't have a problem when they first encounter pneumococcus, but some do. Every year, tens of thousands of children suffer severe pneumococcal infections. Most of these children were previously healthy and well nourished. As with other vaccine-preventable diseases, we don’t know which babies will suffer severe infections. Vaccination removes the possibility of a child becoming severely affected while also preventing millions of more minor infections. 

Pneumococcal infections after influenza

Pneumococcus usually lives in the nose, throat and breathing tubes of people without causing disease. But, if these areas are damaged by an infection like influenza (flu), the bacteria can spread to other areas and cause infections. For example, pneumococcal bacteria can spread to the lungs, bloodstream, brain or spinal cord.

Smoking and increased risk of disease

Activities like smoking can also damage the lining of the nose and throat, allowing for the bacteria to spread and cause disease. For this reason, people who smoke are at higher risk for some infections, like pneumococcus and meningococcus, which can also be prevented by a vaccine. Both can cause meningitis.

Find out more about meningitis in this video discussion between two CHOP doctors.

Grandparents holding grandchild

Pneumococcus Q&A

The vaccine

Several groups of people are at higher risk of severe pneumococcal infections. Babies are recommended to get four doses of pneumococcal vaccine. Many adults can also benefit from being vaccinated against pneumococcus. The number of doses and the vaccine type depend on several factors, including age, health, and pneumococcal vaccination history. For more details on which adults should get this vaccine, see the “Other questions you might have” section of this page.

How is the pneumococcal vaccine made?

Pneumococcal vaccines are available in two types. 

Polysaccharide vaccine — The first type was licensed in 1977. This version contains the sugar coating from 23 types of pneumococcal bacteria. The sugar coating is called a polysaccharide, so the vaccine is often referred to as PPSV23 to denote that it is the pneumococcal polysaccharide vaccine that protects against 23 types of the bacteria. This version is used less frequently than the newer conjugate versions. But because it protects against the most types of pneumococcal bacteria, it is still given to some adults and high-risk younger people.   

Conjugate vaccine — Because children less than 2 years old didn’t develop very good immune responses to the polysaccharide vaccine, there was not a vaccine for children for many years in the U.S. However, scientists figured out a way to make this vaccine so that young children could be protected. This version, called the pneumococcal conjugate vaccine or PCV, became available in 2000. It is made in a manner similar to the vaccine against Haemophilus influenzae type b (Hib; see "How are vaccines made?"). Specifically, the pneumococcal polysaccharides are linked (or conjugated) to a harmless “helper” protein. As children make an immune response to the helper protein, they also make an immune response to the polysaccharides. The result is that antibodies directed against the pneumococcal polysaccharides protect the child without taking the risk that their first encounter with natural pneumococcus will result in severe illness, permanent disabilities or death. Three versions of PCV are available. They differ by how many types of pneumococcal bacteria they protect against. PCV15 protects against 15 types of pneumococcal bacteria. The other two protect against 20 (PCV20) or 21 (PCV21) types. Older versions containing fewer conjugated pneumococcal polysaccharides (PCV7 and PCV13) are no longer available. 

Conjugate vaccines have also been shown to be effective in adults, so they are now used in various age groups of people. Notably, PCV21 was designed to protect high-risk and older adults, so it does not simply have one extra type of polysaccharide compared with PCV20. Rather, it protects against the types that more commonly cause disease in adults: 

  • Both vaccines (PCV20 and PCV21) protect against these 10 types of pneumococcal bacteria: 3, 6A, 7F, 19A, 22F, 33F, 8, 10A, 11A, and 12F.
  • PCV20 (but not PCV21) also protects against types 1, 4, 5, 6B, 9V, 14, 18C, 19F, 23F, and 15B.
  • PCV21 (but not PCV20) also protects against types 9N, 17F, 20, 15A, 15C, 16F, 23A, 23B, 24F, 31, and 35B. 

PCV20 protects adults against the pneumococcal types that cause about 54 to 58 of every 100 cases of severe pneumococcal disease. By switching to the types included in PCV21, protection increases to cover 81 to 85 of every 100 cases of severe pneumococcal disease. 

Finally, an added benefit of the conjugate vaccines is that they also reduce the quantity of bacteria in the vaccinated person’s nose, so they decrease the spread of pneumococcus in the community. This reduced spread benefits everyone in the community because they all have a lower chance for exposure.

What are the side effects of the pneumococcal vaccine?

People vaccinated against pneumococcal can experience mild side effects, including: 

  • Pain or swelling where the shot was given
  • Decreased appetite
  • Irritability
  • Headache
  • Muscle aches 

Some people will also develop a low-grade fever, and a few (about 10 of 100) will develop a higher fever (more than 102 degrees Fahrenheit). 

Young children who get pneumococcal vaccine and the inactivated influenza vaccine (shot) at the same time may be more likely to experience a seizure associated with high fever, called a febrile seizure. Although scary, febrile seizures do not cause long-lasting effects.

Other questions you might have

Why do pneumococcal vaccines include numbers in the name?

About 90 different types of pneumococcal bacteria cause illness, so one major challenge in creating pneumococcal vaccines was protecting against multiple types. The numbers in the name of each pneumococcal vaccine quickly tell us how many types the vaccine protects against (23 for the polysaccharide vaccine and 15 or 20 or 21 for conjugate vaccines).

Is it true that more than one type of infection can cause meningitis?

Yes. Everyone has heard it on the news — the story of a local student with meningitis. These reports cause many questions, concerns and even fear among families with children in the affected school.

There are some important considerations when this happens. First, it is important to remember that meningitis refers to an infection of the lining of the brain and spinal cord. Second, viruses or bacteria can cause meningitis: 

Viral meningitis — This type is more common and typically less severe than bacterial meningitis. Vaccine-preventable diseases that can cause viral meningitis include measles, mumps, chickenpox and influenza.

Bacterial meningitis — Most, but not all, cases of bacterial meningitis can be prevented by vaccination. The most common causes of bacterial meningitis include meningococcus, pneumococcus, and Haemophilus influenzae type B (often referred to as Hib). Fortunately, by the age of 2, most children are fully immunized against pneumococcus and Hib. While we don’t currently have a meningococcal vaccine for infants, adolescents can be protected against meningococcus.

Does the pneumococcal vaccine prevent ear infections in children?

Pneumococcus is a common cause of ear infections in infants and young children. Before a vaccine was available, millions of children would have ear infections caused by pneumococcus each year. However, two points are important. First, other bacteria also cause ear infections in infants and young children. Second, while the pneumococcal vaccine prevents some ear infections, it’s better at preventing severe disease, like pneumonia, meningitis, bloodstream infections and death. It’s estimated that the pneumococcal vaccine prevents between 6 and 15 of every 100 ear infections caused by pneumococcus.

Which adults should get the pneumococcal vaccine?

Many adults are recommended to get the pneumococcal vaccine, but they might not realize it.

Adults 50 years and older who have not been vaccinated against pneumococcus

Adults 50 years and older who have not previously received a pneumococcal vaccine should get either PCV20 alone, PCV21 alone, or PCV15 followed by a dose of PPSV23. In most cases the dose of PPSV23 should be separated by a year, but this interval can be shorter for some people, so individuals should check with their healthcare provider about the timing that is best for their situation.

Adults 50 years and older who were previously vaccinated against pneumococcus

Adults 50 years and older who were previously vaccinated against pneumococcus should talk with their healthcare provider about whether they need the pneumococcal vaccine and if so, which version they need.

Adults 19 to 49 years of age

Adults ages 19 to 49 with immunocompromising conditions, cochlear implants, cerebrospinal fluid leaks, or chronic health conditions, such as alcoholism; chronic heart, liver or lung disease; or diabetes are at higher risk of suffering complications from pneumococcal infections, so they should be vaccinated. People who smoke cigarettes are also recommended to get the pneumococcal vaccine because smoking disrupts the lining of the nose, throat and breathing tubes, increasing the person’s risk for the bacteria to cause severe infection. Those unsure if they need a pneumococcal vaccine should check with their healthcare provider.

Adults in this age group who were already vaccinated against pneumococcus should talk with their healthcare provider to see if they need any more doses.

Relative risks and benefits

Do the benefits of the pneumococcal vaccine outweigh its risks?

Pneumococcal bacteria still cause hundreds of cases of meningitis, bloodstream infections and pneumonia every year in the U.S. Because the pneumococcal vaccine does not cause serious side effects, the benefits of the vaccine clearly outweigh its risks.

Disease risks

  • Pneumonia – symptoms can include high fever, cough, and rapid, difficult breathing
  • Empyema – pus between lung and chest wall
  • Sepsis – bloodstream infection
  • Meningitis – inflammation of the lining of the brain and spinal cord
  • Antibiotics don’t always work
  • Disease can be fatal

Vaccine risks

  • Pain, redness and swelling at the injection site
  • High fever (> 102 degrees Fahrenheit) in up to 10 of 100 recipients
  • Decreased appetite
  • Irritability
  • Young children who get pneumococcal vaccine and the inactivated flu vaccine (shot) at the same time may be more likely to experience a seizure associated with high fever, called a febrile seizure. Although scary, febrile seizures do not cause long-lasting effects.

References

Orenstein W, Offit PA, Edwards KM and Plotkin SA. Pneumococcal conjugate vaccine and pneumococcal common protein vaccines, in Vaccines, 8th Edition, 2024, 826-868.

Orenstein W, Offit PA, Edwards KM, and Plotkin SA. Pneumococcal polysaccharide vaccines, in Vaccines, 8th Edition, 2024, 869-889.

Reviewed by Paul A. Offit, MD, on November 4, 2025