Pneumococcal vaccines
(i) The currently licensed vaccine
The polyvalent polysaccharide vaccine contains per dose (0.5 ml) 25 micrograms of purified capsular polysaccharide from each of the 23 capsular types of S. pneumoniae that together account for most cases (90%) of serious pneumococcal disease in Western industrialized countries. The marketed versions of this vaccine are almost identical. Relatively good antibody responses (60%–70%) are elicited in most healthy adults during the two to three weeks following a single intramuscular or subcutaneous dose of this vaccine. The immune response is unreliable in children under two years of age, and in immunocompromised individuals. Following the vaccination of pregnant women, antibodies are transferred both via the placenta and in the breast milk. However, it is not yet documented that maternal vaccination actually protects newborn infants against pneumococcal disease.
The polyvalent polysaccharide vaccine is recommended for selected groups under two years of age with increased risk of pneumococcal disease. Such groups include healthy elderly people (more than 65 years of age), particularly those living in institutions, and patients suffering from chronic organ failure, diabetes or certain immunodeficiencies. The vaccine has little protective efficacy in some important high-risk groups for pneumococcal disease, such as persons suffering from recurrent otitis media, haematological malignancies or chronic alcoholism. Revaccination after three to six years may be considered in certain high-risk groups such as patients with asplenia or nephrotic syndrome, where immunity following vaccination is known to decline rapidly.
Adverse reactions include some soreness at the site of injection and, more rarely, low-grade fever. Revaccination within less than three years may cause these reactions to become more severe, and is therefore not recommended in immunocompetent persons.
(ii) Candidate pneumococcal vaccines
Several manufacturers are in the process of developing pneumococcal vaccines based on the conjugation of selected capsular polysaccharides to a protein carrier, such as a bacterial toxoid. The protein carriers induce a T-cell dependent immune response to the polysaccharides, leading to immunological memory and boosting upon repeated injection. As the current polysaccharide vaccines may also be used to boost the response to the conjugates, the combined use of these vaccines may be a future cost-saving option. The conjugate vaccines that are currently in advanced stages of development contain 7–11 capsular serotypes, representing the most common causes of invasive pneumococcal disease in children. Significant immunological competition between the antigens included has not been observed. As with polysaccharide vaccines, the conjugate vaccines induce protection only against the serotypes involved; however, higher antibody levels are achieved, and the conjugates elicit an immune response more efficiently in infants and in immunodeficient persons. Several candidate conjugate vaccines have successfully passed the development phases dealing with safety and immunogenicity, and results from the first efficacy trial of a conjugate vaccine in infants show excellent protection against invasive disease. Looked at in comparison with the Hib vaccines, pneumococcal conjugate vaccines have been shown not only to protect against invasive disease, but also to suppress nasopharyngeal carriage of the pathogen. Therefore, these vaccines could possibly prevent even non-invasive pneumococcal disease and reduce bacterial transmission in the community. Such a herd effect would add considerable value to the conjugate vaccines.
At least theoretically, there is a possibility that large-scale use of the conjugate vaccines may result in a shift in prevailing serotypes from those affected by the vaccines to currently less prevalent serotypes. This possibility deserves careful observation, and is one of the reasons why alternative strategies to the development of a pneumococcal vaccine, such as the common protein antigen approach, should be actively pursued. Theoretically, such common antigens could induce universal protection against pneumococcal disease, regardless of the serotype involved.

WHO position on pneumococcal vaccines
(i) The polysaccharide vaccine
The safety of the current polysaccharide vaccines in older children and non-pregnant adults is well documented. In developed countries they have proved effective against serious pneumococcal disease in children under two years of age, and in some of the adult and elderly populations known to be at particular risk from this disease. The main indications for use of the polysaccharide vaccines are:
The protection of healthy elderly people, particularly those living in institutions;
Patients with chronic organ failure;
Particular immunodeficiencies;
The prevention of subsequent pneumococcal infection in patients recovering from proven or assumed pneumococcal pneumonia;
Children at high risk of disease, such as splenectomized children and those with sickle-cell disease.
There is an almost complete lack of information on the burden of pneumococcal disease among adults and the elderly population in developing regions. This illustrates the urgent need for further epidemiological and disease-burden studies on pneumococcal disease. Properly designed phase III trials may provide information both on efficacy and disease burden.
The polysaccharide vaccine has not been used in developing countries where much of the pneumococcal disease burden is found in the under-two age group. Due to poor immune response in children under two years of age, the polysaccharide vaccine is not recommended for routine use in national childhood immunization programmes. The possibility that the vaccine may provide some protection to newborn infants through systematic immunization of pregnant women is currently being investigated.
(ii) Candidate pneumococcal vaccines
Based on immunological considerations and the results of safety, immunogenicity and efficacy trials, the conjugate vaccines are likely to be more efficient than the polysaccharide vaccine for the prevention of pneumococcal disease in children.