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GLOBAL ALLIANCES FOR VACCINES |
Marie Paule Kieny is with the World Health Organization, Geneva, Switzerland. Jean-Louis Excler is with the International AIDS Vaccine Initiative, Delhi, India. At the time of this study, Marc Girard was with the Foundation Biomérieux, Annecy, France.
Correspondence: Requests for reprints should be sent to Marie Paule Kieny, PhD, Initiative for Vaccine Research, World Health Organization, Avenue Appia 20, CH1211-Genève 27, Switzerland (e-mail: kienym{at}who.int).
| ABSTRACT |
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Infectious diseases are responsible for approximately 25% of global mortality, especially in children aged younger than 5 years. Much of the burden of infectious diseases could be alleviated if appropriate mechanisms could be put in place to ensure access for all children to basic vaccines, regardless of geographical location or economic status. In addition, new safe and effective vaccines should be developed for a variety of infections against which no effective preventive intervention measure is either available or practical.
The public, private, and philanthropic sectors need to join forces to ensure that these new or improved vaccines are fully developed and become accessible to the populations in need as quickly as possible.
| INTRODUCTION |
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However, the worlds poorest regions are still suffering a heavy toll of premature deaths and disabilities from infectious diseases for which vaccines do not exist, or need to be improved.3 Infectious diseases are still responsible for at least 15 million deaths per year, making them the largest contributors to the disparity in average life span between rich and poor countries (77 and 52 years, respectively). In addition to this high death toll, millions of children are suffering from disability and illness because they have not been properly immunized. The most effective way to reduce disease and deaths from infectious diseases is to vaccinate populations at risk. Unfortunately, vaccines are still missing for a number of pathogens, and some of the existing vaccines are not completely protective. For these diseases, it is of crucial importance that research and development of vaccines be a priority.
The following is an overview of a few selected fields of current vaccine development.
| DIARRHEAL DISEASES |
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Rotavirus is the leading cause of severe diarrheal disease and dehydration of infants in both industrialized and developing countries. By age 3 to 4 years, virtually all children have had the disease. Rotavirus is responsible for 25% of deaths associated with diarrhea and for 6% of all deaths in children younger than 5 years of age.
Rotavirus is a double-stranded RNA virus belonging to the Reoviridae family. In the United States, an oral live tetravalent rhesushuman reassortant vaccine was licensed in 1998; recommended for the routine immunization of infants, it was administered to more than 900 000 children. Efficacy estimates were around 55% against all cases of rotavirus diarrhea and over 70% against severe disease. However, an increased frequency of a rare but severe vaccine-associated side effect, called intussusception, was demonstrated, leading to the vaccines withdrawal from the market in 1999. Unfortunately, the vaccine, which was undergoing testing concomitantly in Asia and Africa, could not be evaluated in terms of risk-benefit for children in developing countries since the trials were stopped.
A lamb-derived monovalent live-attenuated oral vaccine is licensed in China, but the vaccine cannot be distributed on the international market at present. Several new vaccine approaches are currently being pursued:
It remains to be seen whether intussusception will be associated with any of these new rotavirus vaccines, and several alternative vaccine approaches have been proposed to avoid this potential adverse event.
| ACUTE RESPIRATORY INFECTIONS |
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The sudden emergence in early 2003 of an epidemic of atypical pneumonia originating in China led to the identification of the severe acute respiratory syndrome (SARS) virus, a coronavirus unrelated to previously known coronaviruses. The virus was later recovered from Chinese masked palm civets and raccoon dogs, which might have acted as an intermediate host between an as yet unidentified natural virus reservoir and man. The development of a vaccine against SARS has been judged a global priority, but it is still only at the early clinical stage.
| RSV |
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RSV belongs to the Paramyxoviridae family, genus Pneumovirus. Two subgroups, A and B, have been described, primarily based on differences in the antigenicity of the surface glycoprotein (G). Two factors have complicated the development of vaccines to prevent RSV infection. First, host immune responses appear to play a role in the pathogenesis of disease, as early studies with a Formalin-inactivated vaccine showed that vaccine recipients suffered from more severe disease. Second, naturally acquired immunity is neither complete nor durable and recurrent infections occur frequently. Purified fusion protein vaccines have been shown to be safe and immunogenic in 12- to 48-month-old children. A subunit vaccine containing the RSV F, G, and M proteins, now in phase II in Canada and Australia, has exhibited an excellent safety and immunogenicity profile. Another candidate vaccine is a synthetic peptide of the conserved region of the G protein administered intranasally. Live attenuated RSV vaccines based on temperature-sensitive, cold-adapted strains of the virus that could be delivered to the respiratory mucosa are probably among the most promising approaches.
S pneumoniae
Infections caused by pneumococci are a major cause of morbidity and mortality all over the world. Pneumonia, febrile bacteremia, and meningitis are the most common manifestations of the disease. The highest rates of pneumococcal disease occur among young children and the elderly. Pneumococci are estimated to cause over 1 million deaths, most of which occur in developing countries, where they probably are the most important pathogen of early infancy. In Europe and the United States, pneumococcal pneumonia is the most common community-acquired bacterial pneumonia, estimated to affect approximately 100 adults per 100 000 each year. In developing countries, infants aged younger than 3 months are especially at risk of pneumococcal meningitis. Even in economically developed regions, invasive pneumococcal disease carries mortality rates of 10% to 20%, and the rate may exceed 50% in high-risk groups.
S pneumoniae is a gram-positive encapsulated bacteria of which about 90 different polysaccharide capsule serotypes have been identified. Most pneumococcal disease in infants is associated with the 11 most common serotypes, which cause at least 75% of invasive disease in all regions. Pneumococcal resistance to essential antibiotics is a serious and rapidly increasing problem worldwide.
Protective immunity against pneumococci is provided by type-specific anticapsular antibodies. However, capsular polysaccharide vaccines do not regularly elicit protective levels of antibodies in children aged younger than 2 years, or in immunocompromised individuals. One of the currently licensed vaccines contains purified capsular polysac-charide from each of the 23 capsular types of S pneumoniae, which together account for most cases (90%) of serious pneumococcal disease in Western industrialized countries. Relatively good antibody responses are elicited in adults. In some countries, vaccination is recommended for elderly people, particularly those living in institutions.
Experience with Haemophilus influenzae type B conjugate vaccines has shown that the immunogenicity of polysaccharide can be improved by chemical conjugation to a protein carrier, thereby eliciting a T-celldependent antibody response. Unlike polysac-charide vaccines, conjugate vaccines induce high antibody levels and elicit an immune response in infants and in immunodeficient persons. Moreover, these vaccines induce immunological memory. Therefore, they could reduce bacterial transmission in the community. Introduction of a 7-valent conjugate vaccine in the United States resulted in a dramatic decline in the rates of invasive disease. The vaccine also showed moderate protection against otitis caused by vaccine serotypes. However, the decrease in vaccine-type otitis media was partially offset by an increase in disease caused by nonvaccine types of S pneumoniae and by H influenzae, a phenomenon referred to as "replacement disease."
The development and introduction in developing countries of a conjugate S pneumoniae vaccine is now one of the highest-priority projects. Several conjugate vaccines that provide more optimal serotype coverage in developing countries than the currently licensed 7-valent vaccine are in clinical development. They may be available by 2008 to 2010 for vaccination programs in developing countries, although presumably at a high price.
| MENINGOCOCCAL MENINGITIS |
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Group A meningococcus has historically been the main cause of epidemic meningococcal disease and still predominates in Africa during both endemic and epidemic periods. The highest burden of disease occurs in sub-Saharan Africa in an area extending from Senegal and Ethiopia, referred to as the "meningitis belt." Epidemics occur in irregular cycles, lasting for 2 to 3 dry seasons and dying out during the intervening rainy seasons. The size of these epidemics can be enormous: in 1996, around 200 000 cases were reported, with 20 000 deaths. In the last few years, the emergence of group W-135 as the cause of epidemics has added complexity to the epidemiological situation in the region.
Group B meningococcus accounts for approximately 50% of meningococcal meningitis cases in North America and Europe. In all countries, the incidence of group B disease is highest in infants. Group B epidemics have occurred in the United States, Cuba, Brazil, and Chile. Since 1991, New Zealand has experienced a large epidemic of group B meningococcal infection, with incidence rates up to 10 times the background incidence. Altogether, meningococcus serogroup B incidence may be estimated at between 20 000 and 80 000 cases per year, with 2000 to 8000 deaths.
Polysaccharide vaccines against N meningitidis groups A, C, Y, and W-135 are available worldwide, although in restricted quantities, and with a price for the tetravalent vaccine that does not allow widespread use in sub-Saharan Africa. The emergence of the W-135 serogroup in some countries of Africa has prompted the development of a cheaper trivalent polysaccharide A/C/W-135 vaccine. However, polysaccharide vaccines are poor immunogens in young infants and fail to induce immunological memory. In 1999, meningococcal group C conjugate vaccine was successfully introduced into the routine British immunization program, opening the way for the development of conjugate vaccines against the other N meningitidis serogroups. Vaccine manufacturers are currently developing conjugate vaccine combinations incorporating groups A, C, Y, and W-135 polysaccharides.
These multivalent meningococcal polysaccharideprotein conjugate vaccines will be available in the United States and Europe within a few years. Nevertheless, it is unlikely that these new vaccines will be available at a price affordable to most of the countries in the African meningitis belt. Therefore, a public partnership between the World Health Organization (WHO) and the Program for Appropriate Technology in Health (a US-based nongovernmental organization), the Meningitis Vaccine Project, is currently developing a serogroup A conjugate vaccine tailored for Africa that will be available at a price of less than US $1 per dose.
Serogroup B capsular polysac-charide is a poor immunogen, probably because it is structurally identical to glycoproteins expressed by host tissues. Consequently, vaccine research directed against serogroup B meningococcus has focused largely on cell-surface protein antigens (outer membrane proteins). The 2 most-studied outer-membrane-protein vaccines are those produced in response to outbreaks in Norway and Cuba. Both have been used for epidemic control in their respective countries and were found to be 50% to 80% effective.
| HIV/AIDS |
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Human immunodeficiency viruses belong to the Lentivirus group of the Retroviridae family. Two types have been described: HIV-1 and HIV-2, the former appearing more aggressive and spreading more rapidly. The development of a safe and effective HIV vaccine is hampered by the tremendous genetic variability of the virus and the paucity of knowledge on possible immune mechanisms of protection. The first clinical trial of an HIV vaccine was conducted in the United States in 1987. Since then, over 30 candidate vaccines have been tested in over 80 phase I/II clinical trials, involving over 10 000 healthy volunteers. Most of these trials have been conducted in the United States and Europe. A few trials also have been conducted in developing countries (Brazil, China, Cuba, Haiti, Kenya, Thailand, Trinidad, and Uganda). The effort to develop and evaluate HIV vaccines will be strengthened by the African AIDS Vaccine Programme, which was established following an initiative of WHO and the Joint United Nations Programme on HIV/AIDS (UNAIDS), and by a new initiative involving, among others, the Bill and Melinda Gates Foundation, the International AIDS Vaccine Initiative, and the US National Institutes of Health.4
Only 2 efficacy trials have been completed so far, both using the same approach of a subunit gp120 envelope glycoprotein, one in the United States (with sites in Canada and Europe) and the other in Thailand. The 120 kDa glycoprotein (gp120) is the major antigenic determinant present on the surface of HIV particles. Definite results from both trials were reported in 2003, demonstrating that immunization did not result in a statistically significant reduction of HIV infection within the study populations. A third efficacy trial involves a live recombinant vector (canarypox-HIV) expressing the gag, env, and pol genes of HIV-1 and combined in a prime-boost vaccination regimen with a gp120 subunit vaccine; begun in Thailand in late 2003, it aims to include 16 000 volunteers. Other interesting approaches being tested in humans are based on DNA prime and recombinant poxvirus boosts. These vaccines are not intended to prevent HIV infection but to elicit a T-cell immune response that could prevent or delay the occurrence of the disease.
Recombinant adenoviruses represent another promising approach of the same type, especially when combined with a recombinant canarypox in a prime-boost vaccination regimen. Other candidate vaccines include other recombinant bacterial or viral vectors, some of which have shown some promise in controlling viral replication in preclinical studies in nonhuman primate models. Subunit HIV vaccines based on engineered recombinant envelope glycoproteins alone or combined with the non-structural Tat, Nef, and Rev proteins, DNA vaccines and peptides also are under development.
There is no doubt that the development of a safe, effective, and affordable HIV vaccine remains the scientific and public health challenge of this new century.
| HUMAN PAPILLOMAVIRUS |
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HPV belongs to the Papovaviridae family. More than 30 types of HPV have been identified that can infect the genital mucosa. It has been established that over 95% of cervical cancer biopsies contain HPV DNA, with oncogenic HPV-16, -18, -33, and -45 comprising more than 80% of the cases. The association of cervical cancer with the presence of sexually transmitted HPV DNA has substantiated the basis for vaccine development. Viral recombinant proteins are being studied as antigenic components of vaccine candidates. Prophylactic vaccine candidates are based on the recombinant capsid proteins L1 and L2, which self-assemble into viruslike particles (VLPs) that can induce virus-neutralizing antibodies, while therapeutic vaccine candidates, based on viral oncogenic proteins E6 and E7, are designed to induce cell-mediated immune responses able to eliminate infected cells.
The results of a controlled efficacy trial of HPV-16 VLPs became available recently and showed that the incidence of persistent HPV-16 infection and HPV-16-related cervical intraepithelial neoplasia was reduced in vaccinated women, with a 100% efficacy rate over a 1.7-year follow-up period. These results suggest that immunizing HPV-16-negative women will eventually reduce the incidence of cervical cancer. Two prophylactic vaccine candidates are at the level of phase III efficacy evaluation: a bivalent HPV-16/18 VLP vaccine produced in insect cells using a recombinant baculovirus, and a tetravalent HPV-6/11/16/18 VLP vaccine produced in recombinant yeast.
| CONCLUSION |
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It is nevertheless vital to continuously develop new vaccines and to improve existing ones.10 In this context, a new paradigm needs to be developed to include and coordinate the actions of the WHO, international and national funding agencies, the pharmaceutical industry and manufacturers in emerging developing countries, nonprofit foundations, and nongovernmental humanitarian organizations. Working together, these organizations could harness existing potentials and accelerate the development and testing of new vaccines and the improvement and implementation of existing vaccines. The goal is to offer better safety, efficacy, and delivery methods with lower costs of production, leading to a more efficient distribution and better availability of vaccines, especially in developing countries.
| Acknowledgments |
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| Footnotes |
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Contributors
Each author contributed to researching and composing this article.
Accepted for publication February 5, 2004.
| References |
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2. State of the Worlds Vaccine and Immunization. Rev ed. Geneva, Switzerland: World Health Organization; 2003.
3. Widdus R. Publicprivate partnerships for health: their maintargets, their diversity, and their future directions. Bull World Health Organ.2001;79(8): 713720.[Web of Science][Medline]
4. Klausner RD, Fauci AS, Corey L, et al. The need for a global HIV vaccine enterprise. Science.2003;300: 20362039.
5. Ellis RW. Technologies for making new vaccines. In: Plotkin SA, Orenstein WA, eds. Vaccines. 4th ed. Philadelphia, Pa: Elsevier Saunders; 2004:11771197.
6. Proceedings of the Fourth Global Vaccine Research Forum. Geneva, Switzerland: World Health Organization; 2004.
7. Struck MM. Vaccine R&D success rates and development times. Nat Biotechnol.1996;14(5):591593.[Web of Science][Medline]
8. André FE. How the research-based industry approaches vaccine development and establishes priorities. Dev Biol (Basel).2002;110:2529.
9. Greco M. The future of vaccines: an industrial perspective. Vaccine.2001; 20(suppl 1):S101S103.
10. Bloom BR, Lambert P-H, eds. The Vaccine Book. San Diego, Calif: Academic Press; 2003.
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