出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/08/20 15:50:19」(JST)
A pneumococcal vaccine is a vaccine against Streptococcus pneumoniae.[1]
Types include: pneumococcal polysaccharide vaccine and pneumococcal conjugate vaccine
It is on the World Health Organization's List of Essential Medicines, a list of the most important medication needed in a basic health system.[2]
The polysaccharide vaccine most commonly used today.[citation needed] consists of purified polysaccharides from 23 serotypes (1, 2, 3, 4, 5, 6b, 7F, 8,9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19F, 19A, 20, 22F, 23F and 33F).[3] Immunity is induced primarily through stimulation of B-cells which release IgM[3] without the assistance of T cells.[4]
This immune response is less robust than the response provoked by conjugated vaccines, which has several consequences. The vaccine is ineffective in children less than two years old, presumably due to their less mature immune systems.[3] Non-responders are also common amongst older adults.[3] Immunization is not lifelong, so individuals must be re-vaccinated every 5–6 years.[3] Since no mucosal immunity is provoked, the vaccine does not affect carrier rates, promote herd immunity, or protect from upper or lower respiratory tract infections.[3] Finally, provoking immune responses using unconjugated polysaccharides from the capsules of other bacteria, such as H. influenzae, have proven significantly more difficult.[3]
The conjugated vaccine consists of capsular polysaccharides covalently bound to the diphtheria toxoid CRM197, which is highly immunogenic but non-toxic.[3] This combination provokes a significantly more robust immune response by recruiting CRM197-specific type 2 helper T cells, which allow for immunoglobulin type switching (to produce non-IgM immunoglobulin) and production of memory B cells.[3] Among other things, this results in mucosal immunity and eventual establishment of lifelong immunity after several exposures.[3] The main drawbacks to conjugated vaccines are that they only provide protection against a subset of the serotypes covered by the polysaccharide vaccines.
In the USA, a heptavalent pneumococcal conjugate vaccine (PCV 7) (e.g. Prevenar[5]) was recommended for all children aged 2–23 months and for at-risk children aged 24–59 months in 2000. The normal 4-dose series is given at 2, 4, 6 & 12–14 months of age. In February 2010, a pneumococcal congugate vaccine which protects against an additional 6 serotypes was introduced (PCV 13 / brand name: Prevnar 13) and can be given instead of the original Prevnar.[6][7] Similar 9-, and 10-valent vaccines have been tested. Protection is good against deep pneumococcal infections (especially septicemia and meningitis). However, if a child is exposed to a serotype of pneumococcus that is not contained in the vaccine, he/she is not afforded any protection. This limitation, and the ability of capsular-polysaccharide conjugate vaccines to promote the spread of non-covered serotypes, has led to research into vaccines that would provide species-wide protection.
Pneumococcal polysaccharide vaccine (Pneumovax is one brand) gives at least 85% protection in those under 55 years of age for five years or longer. Immunization is suggested for those at highest risk of infection, including those 65 years or older; generally the vaccine should be a single lifetime dose, as there is a high risk of side effects if repeated. The standard 23-valent vaccines are ineffective for children under two years old.
The current guidelines of the American College of Physicians call for administration of the immunization between ages 2 and 65 when indicated, or at age 65. If someone received the immunization before age 60, the guidelines call for a one-time revaccination.
Revaccination at periodic intervals is also indicated for those with other conditions such as asplenia or nephrotic syndrome.
It was announced in February 2006 that the UK government would introduce vaccination with the conjugate vaccine in children aged 2, 4 and 13 months.[8][9] This included changes to the immunisation programme in general.[10] In 2009, the European Medicines Agency approved the use of a 10-valent pneumcoccal conjugate vaccine for use in Europe.[11] The 13 valent pneumococcal vaccine was introduced in the routine immunisation schedule of the UK in April 2010.
Pneumovax 23 is used, and according to the enclosed patient information leaflet, has a reported 76% to 92% protective efficacy (pneumococcal types 1, 2, 3, 4, 5, 6B**, 7F, 8, 9N, 9V**, 10A, 11A, 12F, 14**, 15B, 17F, 18C, 19A**, 19F**, 20, 22F, 23F** and 33F** are included, where ** indicates drug resistant pneumococcal infections; these are the 23 most prevalent or invasive pneumococcal types of Streptococcus pneumoniae).
Pneumococcal vaccines Accelerated Development and Introduction Plan (PnemoADIP) is a program to accelerate the evaluation and access to new pneumococcal vaccines in the developing world. PneumoADIP is funded by the Global Alliance for Vaccines and Immunization (GAVI). Thirty GAVI countries have expressed interest in participating by 2010. PneumoADIP aims to save 5.4 million children by 2030.[12]
A pilot Advance Market Commitment (AMC) to develop a vaccine against pneumococcus was launched in June 2009 as a strategy to address two of the major policy challenges to vaccine introduction: a lack of affordable vaccines on the market, and insufficient commercial incentives to develop vaccines for diseases concentrated in developing countries. Under the terms of an AMC, donors make a legally binding guarantee that,if a future vaccine is developed against a particular disease, they will purchase a predetermined amount at an agreed-upon price. The guarantee is linked to safety and efficacy standards that the vaccine must meet and is structured in a way to allow several firms to compete to develop and produce the best possible new product. AMCs reduce risk to donor governments by eliminating the need to fund individual research and development projects that may never produce a vaccine. If no company produces a vaccine that meets the predetermined standards, governments (and thus their taxpayers) spend nothing. For the bio-pharmaceutical industry, AMCs create a guaranteed market, with a promise of returns that would not normally exist. For developing countries, AMCs provide funding to ensure that those vaccines will be affordable once they have been developed. It is estimated that the pneumococcal AMC could prevent more than 1.5 million childhood deaths by 2020.[13]
Due to the geographic distribution of pneumococcal serotypes, additional research is needed to find the most efficacious vaccine for developing-world populations. In a previous study, the most common pneumococcal serotypes or groups from developed countries were found to be, in descending order, 14, 6, 19, 18, 9, 23, 7, 4, 1 and 15. In developing countries the order was 6, 14, 8, 5, 1, 19, 9, 23, 18, 15 and 7.[14] In order to further pneumococcal vaccine research and reduce childhood mortality, five countries and the Bill & Melinda Gates Foundation established a pilot Advance Market Commitment for pneumococal vaccines worth US$1.5 billion. Advance Market Commitments are a new approach to public health funding designed to stimulate the development and manufacture of vaccines for developing countries.[15]
There is currently research into producing vaccines than can be given into the nose rather than by injection.[16] [17] It is believed that this improves vaccine efficacy and also avoids the need for injection.
The development of serotype-specific anticapsular monoclonal antibodies has also been researched in recent years. These antibodies have been shown to prolong survival in a mouse model of pneumococcal infection characterized by a reduction in bacterial loads and a suppression of the host inflammatory response.[18][19] Additional pneumococcal vaccine research is taking place to find a vaccine that offers broad protection against pneumococcal disease.[20]
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| リンク元 | 「PCV7」 |
| 関連記事 | 「pneumococcal」 |