Vaccination greatly reduces disease, disability, death and inequity worldwide.

In low-income countries, infectious diseases still account for a large proportion of deaths, highlighting health inequities largely caused by economic differences. Vaccination can cut health-care costs and reduce these inequities. Disease control, elimination or eradication can save billions of US dollars for communities and countries. Vaccines have lowered the incidence of hepatocellular carcinoma and will control cervical cancer. Travellers can be protected against "exotic" diseases by appropriate vaccination. Vaccines are considered indispensable against bioterrorism. They can combat resistance to antibiotics in some pathogens. Noncommunicable diseases, such as ischaemic heart disease, could also be reduced by influenza vaccination. Immunization programmes have improved the primary care infrastructure in developing countries, lowered mortality in childhood and empowered women to better plan their families, with consequent health, social and economic benefits. Vaccination helps economic growth everywhere, because of lower morbidity and mortality. The annual return on investment in vaccination has been calculated to be between 12% and 18%. Vaccination leads to increased life expectancy. Long healthy lives are now recognized as a prerequisite for wealth, and wealth promotes health. Vaccines are thus efficient tools to reduce disparities in wealth and inequities in health.

Universal mass vaccination against hepatitis A.

When first introduced in 1992 the hepatitis A vaccine was recommended for individuals at high risk of exposure. This policy was not expected to have a significant impact on disease incidence at population level in view of the epidemiology of the hepatitis A virus (HAV). More recently two countries, Israel and Bahrain, and regions or subpopulations in others (Australia, China, Byelorussia, Italy, Spain, US) have embarked upon more ambitious vaccination programmes that aim to immunize whole birth cohorts. After a brief survey of the virology and epidemiology of HAV, the disease burden it inflicts and a short history of the development of HAV vaccines--both live (in China) and killed vaccines are available--he vaccination programmes introduced in the countries mentioned above are described. The results have been spectacular: disease incidence, not only in the vaccinated cohorts but also in the whole population, have plummeted within a few years of the start of mass vaccination. There is now convincing evidence that the vaccine confers herd immunity if the main spreaders of the virus are targeted for immunization. This finding should encourage other countries to start mass vaccination programmes against HAV, particularly as pharmacoeconomic studies are beginning to show that such a strategy could be a cost-effective way of controlling the disease. It is now even conceivable to eradicate HAV. In fact, this should be easier to achieve than polio eradication as HAV vaccines confer more durable immunity than polio vaccines. However, the global disease burden of HAV is generally thought not to be high enough to justify such an undertaking in the foreseeable future.

How the research-based industry approaches vaccine development and establishes priorities.

Over the past two decades, progress in immunology, molecular biology and genomics as well as some technological breakthroughs in computer science has opened the way to the development of prophylactic vaccines against most acute infectious diseases. Therapeutic vaccines against chronic infections, allergic conditions, auto-immune diseases and cancer have also come into the realm of possibility. It is estimated that wordwide there are about 400 vaccine projects in R&D laboratories of academic institutions, research institutes and vaccine manufacturers. Most of these projects will not yield a licensed vaccine for routine or even targeted immunisation. This is mostly not because of scientific barriers but due to financial and politicoeconomic obstades that make their development feasible only by the handful of major research-based vaccine manufacturers that nowadays all form part of large global pharmaceutical corporations. Such enterprises have to be profitable to survive and priority setting, when it comes to R&D projects, has to take into account potential return on all investments, particularly as it currently costs between 200 and 500 million US dollars to bring a new vaccine from the concept stage to market. Factors that influence the decision to embark upon an R&D project on a new vaccine include the medical need for the vaccine, gauged by the global burden of the targeted disease, potential and probable market size - judged on volume (number of doses required) and value (total sales) -, probability of success and expertise of the company in the field (both R&D and marketing) as well as the likelihood of competitors taking a large part of the market. Moral imperatives such as the urgent need for vaccines against HIV/AIDS, malaria and an improved vaccine against tuberculosis to save the several millions of lives claimed each year by these diseases also play a role. However, for such investments to be sustainable other sources of financing than the commercial market will be required.

The future of vaccines, immunisation concepts and practice.

Vaccines have prevented more deaths, disability and suffering than any other medical discovery or intervention. Recent breakthroughs in immunology and genomics offer the prospect of the development of many new prophylactic and therapeutic vaccines not only against infectious diseases but also for use in conditions such as allergy, autoimmunity and carcinogenesis where malfunction of the immune system undoubtedly plays a role. These hopeful perspectives are however dimmed by several counterproductive societal trends that include the spreading-although unjustified-belief that vaccines are not safe and may even be unnecessary, escalating costs of vaccine research, development, production and control that are exacerbated by political pressure on selling prices and expensive lawsuits by 'victims' of vaccination who claim excessive compensation. Negative media coverage of vaccine issues is adversely affecting acceptance of vaccination. In spite of these negative trends, vaccines should have a bright future, because it is increasingly being realised that prevention is not only better than cure but it is often also more cost-effective. A better understanding of the dynamics of microbial transmission in populations is leading to more rational immunisation practices on a global scale that could lead to eradication of several pathogens. Attention is being given to making vaccines more user-friendly through the development of combined vaccines and the introduction of less invasive inoculation techniques.

Strengths and weaknesses of current polio vaccines--a view from industry.

Polio eradication is within our grasp and, unless something terribly wrong and unexpected happens, the three types of wild polioviruses will cease to circulate in human populations within the next few years. This achievement will be a result of the rational use of OPV. A momentous global decision--discontinuation of vaccination--will then have to be taken. The most important uncertainty that will weigh upon that decision is whether wild polioviruses can re-emerge after "eradication" defined as "complete interruption of wild polioviruses transmission", has been obtained. It is important to realise that "eradication" does not mean "extinction" in the sense that the dodo is extinct. After eradication, wild polioviruses will still lurk in laboratory specimens and in protected environmental sites (like glaciers) and may even "re-emerge" by back mutation or recombination of Sabin-derived strains that may continue to circulate even after OPV use is discontinued. Theoretically, the risk of re-emergence of wild polioviruses would be lessened if IPV was used for a number of years to immunise all those born after cessation of OPV usage. But the question is "by how much?". Vaccination with IPV will reduce the risk that persistent OPV-derived strains (e.g. in immunodeficient patients) will have the chance to establish permanent transmission after vaccination is totally discontinued. However, the risk of re-emergence will not be changed since this will be determined by the risk of accidental re-introduction. Whether the expense of switching completely from OPV to IPV globally can be justified will depend upon the relative risks of wild poliovirus re-emergence from either OPV-derived sources or other environmental sources including "escape" of virulent seed viruses from IPV production facilities. This balance of probabilities and risks will be very difficult to determine. In any case, it is likely that the decision to upscale IPV production to required levels has already been delayed too long so that polio eradication will be achieved by the use of OPV in developed as well as in less developed countries that cannot afford to use IPV at a high enough vaccine coverage rate to make it safe. Wild poLiovirus transmission has been interrupted with OPV in the Western Hemisphere. There is no reason why this cannot be done in the rest of the world. In industrialized countries that can afford it and where vaccine coverage is sufficient to prevent wild virus circulation, IPV, in combined vaccines, will be increasingly used. Let us hope that politicians in developing countries and zealous ethicists in the developed world will understand why, in the present and foreseeable future circumstances, OPV is better than IPV in the poorer countries and will not demand, in the name of equity in health, a total switch to IPV. For eradication, IPV cannot, and hopefully need not, replace OPV. At this stage it should not.

Is there a causal link between hepatitis B vaccination and multiple sclerosis?

After the publication of case reports of hepatitis B vaccinees with onset or relapse of multiple sclerosis (MS), followed by a media-driven scare campaign in France, the perception that hepatitis B vaccine causes MS has developed. This has led to a fall in the acceptance of hepatitis B vaccination particularly in French-speaking communities which was accelerated by court decisions in favour of vaccination "victims" and the suspension of routine vaccination of pre-adolescents in French schools as a "precautionary measure". This situation has arisen in spite of the absence of scientific data to support a causal link between vaccination and multiple sclerosis. In this article, initially written to inform and reassure employees of one of the vaccine manufacturers, the epidemiological importance of hepatitis B and current knowledge on the aetiology of MS are described. All available data that may throw light on the hypothesis that hepatitis B vaccination is causally linked to MS was reviewed. The conclusion reached on the basis of available data is that the most plausible explanation for the observed temporal association between vaccination and MS is that it is a coincidental association. It is now important to rebuild public confidence in hepatitis B vaccine as well as in vaccination in general.

Development and clinical application of new polyvalent combined paediatric vaccines.

The availability of combined vaccines containing protective antigens against the majority of (ideally all) diseases for which universal immunization is recommended in infancy would simplify the implementation, increase the acceptance, reduce the global cost of immunization programmes and improve disease control, while offering the possibility of disease elimination or even pathogen eradication. The desirability of combined vaccines is further enhanced, and made more urgent, because of the increasing number of diseases that can be prevented by vaccination. The complicated logistics of administering different vaccines that each require several inoculations is a significant barrier to successful immunization of a population. Furthermore, interest in immunization is continuously gaining momentum since it is now generally recognised that vaccines are among the safest and most cost-effective medical interventions for infectious diseases that continue, in spite of the widespread use of efficacious antimicrobial drugs, to be an important cause of morbidity and mortality. This burden is likely to increase due to the development of antimicrobial resistance. Basic research on new vaccines or improvement of existing ones such as the use of new technologies may be carried out in academic or other non-industrial laboratories but development work, including the necessary extensive clinical testing, that lead to products that can be approved for routine use is usually co-ordinated and financed by commercial companies. The decision to develop any particular combined vaccine will therefore be influenced not only by its medical desirability and technical feasibility but also the potential financial returns that the required investments in time and resources may bring to the company. All major vaccine manufacturers are currently working, either alone or through strategic alliances, towards developing more polyvalent vaccines by adding antigens such as inactivated polio virus, conjugated Haemophilus influenzae type b polysaccharide and hepatitis B surface antigen to the diphtheria-tetanus-pertussis vaccine either in its 'classical' (whole-cell) or more purified (acellular) formulations. Experience is showing that the development of combined vaccines involves much more than the simple mixing of existing antigens. Possible incompatibilities or mutual interferences between the antigens themselves, or between excipients, preservatives, adjuvants, residual contaminants, stabilisers and suspending fluids make it mandatory that each formulation be thoroughly tested for quality, stability, efficacy and safety. Furthermore the ability to produce and control it consistently must be established before it can be licensed for commercial use. The progress being made in this field is reviewed.

A phased approach to clinical testing: criteria for progressing from Phase I to Phase II to Phase III studies.

The overall intent of clinical testing is to establish, in a series of phased studies, the clinical tolerance and acceptable "safety" of the candidate vaccine, as well as the type, level and persistence of the immune response after its inoculation, to a representative target population, according to a convenient administration schedule. The final stages involve the direct or indirect demonstration of protective efficacy, if possible in the population(s) for which the vaccine is intended. In addition, consistency of production must be demonstrated. At all these stages, the amount of prior information from preclinical and other studies affects and informs the objectives and design of subsequent studies. Progression from one testing phase to the next is dependent upon attaining the pre-set objectives of each series of studies. The precise objectives to be met will be decided on a case-by-case basis. The earliest assessments in humans (Phase I) involve evaluation of short-term clinical tolerance as measured by local and general reactogenicity, and gross assessments of immunogenicity, in a small number of highly selected individuals in an idealised situation. The selection of "optimal" dose and schedule are the result of further dose-ranging investigations (Phase II), involving more volunteers, with longer, more detailed follow-up assessments. It is at this stage that the accumulated evidence on its immunogenicity profile should be sufficient to assess whether or not the vaccine is worthy of further development. The next level of investigation (Phase III) aims to measure with greater precision the vaccine protective efficacy in the intended target population(s) by comparison of infection and/or disease attack rates in vaccine and placebo recipients. In consistency studies different production lots, manufactured at commercial scale, are tested to demonstrate consistency of manufacture. Additional bridging studies to establish similarity of lots at different production scales, or studies of the duration of the immunity conferred, are conducted in parallel with the progression of the studies in the different phases mentioned above. These latter types of studies are usually carried out concurrently with Phase III studies. This progression continues into the post-marketing period (Phase IV) with surveillance of long term efficacy and observational studies of possible rare adverse events to establish "safety" with more confidence. This paper examines, in general, the aims and designs of studies in each phase as an introduction to the more specific publications that follow.

Immunogenicity of an inactivated hepatitis A vaccine in healthy children: two years' follow-up.

To investigate the long-term immunogenicity of an inactivated hepatitis A vaccine in children, 100 healthy children, aged between 1 and 7 years old and all lacking the antibody to hepatitis A (HA) virus, were enrolled in this trial. They received 3 doses of strain HM 175 HA vaccine with 360 enzyme-linked immunosorbent assay (ELISA) units at 0, 1 and 6 months, respectively. Blood sampling for antibody and aminotransferases was performed 7 days before, then 1, 6, 7, 12, and 24 months after the first dose. The titers of antibody to HA virus were tested by radioimmunoassay and ELISA methods. All subjects became ELISA seropositive at Month 6 after two doses of vaccine. Except for one boy, 99 remained seropositive at Month 24, with a geometric mean titer of 1,148 mIU/ml. Antibody titers for females were significantly higher than those for males throughout the follow-up period. It was concluded that the inactivated HA vaccine used in the present trial was immunogenic and safe in children below seven years old. The vaccine-induced antibody persisted for at least two years in 99% of the vaccinees.

Approaches to a vaccine against hepatitis A: development and manufacture of an inactivated vaccine.

The basis for the development of a vaccine against hepatitis A was laid in the 1970s, when virus was replicated in cell culture. Adaptation to growth in cell culture resulted in attenuation and sufficient quantities of virus particles, allowing the development of both live attenuated and inactivated vaccines. Testing of candidate vaccines in volunteers began in the early 1980s. Recently, a formaldehyde-inactivated whole-virion hepatitis A vaccine, the first licensed vaccine against hepatitis A, was introduced in many countries worldwide, and a live attenuated vaccine became available in the People's Republic of China. Other possible avenues for vaccine development include the use of either conventional or recombinant DNA techniques to obtain subunit vaccines, empty capsids, live viral or bacterial vectors, genetic immunization, synthetic peptides, and anti-idiotypes.

Clinical experience with an inactivated hepatitis A vaccine.

Clinical trials of an inactivated hepatitis A vaccine have encompassed 104 studies completed by December 1993 in 27 countries. Studies involved 50,677 subjects and administration of > 120,000 vaccine doses. Results show that the vaccine is safe, clinically well-tolerated, and highly immunogenic in all age groups. A seroconversion rate of 100% is achieved 1 month after primary vaccination. Vaccine-induced antibody titers persist after a primary vaccination course for > or = 1 year with a single dose of 1440 ELISA units (EL.U.) in adults and after two doses of 360 EL.U. in children. A booster dose 6-12 months after the first vaccine dose induces very high antibody titers, which according to a mathematical model, are expected to protect against hepatitis A for > 20 years. The vaccine is equally immunogenic when administered simultaneously with other traveler vaccines, therefore enabling flexible and convenient vaccination against hepatitis A.

Development of combined vaccines: manufacturers' viewpoint.

Rapid and exciting research breakthroughs in the fields of immunology and molecular biology in recent years have greatly enhanced the potential for developing new vaccines or improving existing ones. The resulting rising number of diseases that can be prevented by vaccination, coupled with the growing trend of preferring cost-effective preventive medical interventions over expensive therapeutic modalities, has increased the complexity of administering to all those who need them, the many different vaccines that will soon be available. Hence attention in the field of vaccinology is now focusing on the development of combined vaccines that, in a few inoculations, can elicit protection against as many diseases as possible. Some of the recent achievements, future objectives and difficulties of vaccine manufacturers in the development of combined vaccines are surveyed.

Single dose inactivated hepatitis A vaccine: rationale and clinical assessment of the safety and immunogenicity.

In comparison with the classical immunisation schedules (0-1-6 or 0-1-12 months) for hepatitis A, a 0- and 12- or a 0- and 6-month schedule would have important advantages by reducing the number of injections and discomfort and increasing scheduling convenience and patient compliance. It would be convenient if a single dose with enough antigen could protect both rapidly and for at least 12 months, when the booster dose would be given. Several clinical trials have been carried out with an inactivated hepatitis A vaccine containing 1,440 EL.U. (1 ml), according to a 0-12 and a 0-6 vaccination schedule. This hepatitis A vaccine is safe and well tolerated. It offers a rapid seroresponse: 14 days after a single dose the seroconversion is 88% (95% C.I.: 84.6-90.9). The 0-12 schedule study showed good persistence of hepatitis A virus (HAV) antibodies with a seroconversion rate of almost 95% at month 12. Booster doses given at 6 or 12 months result in a substantial rise in antibody levels; according to these antibody titres, the 1,440 EL.U. vaccine can be expected to confer comparable duration of protection as the 720 EL.U. vaccine, i.e., 10-20 years. Preliminary data show that timing of the booster may not be critical for the antibody response. In conclusion, the 1,440 EL.U. hepatitis A vaccine is safe, offers rapid seroconversion, and is highly immunogenic. The persistence of HAV antibodies until month 12 allows a certain flexibility in the administration of the booster: month 6 or 12, and a 0-12 or 0-6 schedule can increase the vaccination compliance.

Clinical and immunological investigation of a new combined hepatitis A and hepatitis B vaccine.

As with hepatitis B vaccines, the recently developed hepatitis A vaccine is suitable not only for individual protection, but also for public health control measures. For introduction into routine immunisation programmes, however, hepatitis A vaccine should preferably be combined with other already established vaccines. In particular, a combination of hepatitis A and hepatitis B vaccines would be appropriate. We investigated a new combined hepatitis A/hepatitis B vaccine comparing its tolerability and immunogenicity with that obtained after separate or mixed simultaneous administration of the two components. Three groups of healthy volunteers, each of approximately 50 persons, were included. All were negative for hepatitis A and hepatitis B markers and had normal liver enzyme values. They received hepatitis A (720 ELISA units) and hepatitis B (20 micrograms) vaccines in the deltoid muscle, combined, mixed or separately, according to a 0, 1, 6-month schedule. Blood samples for determination of antibodies to hepatitis A virus (anti-HAV) and hepatitis B virus (anti-HBs) and of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were drawn at months 0, 1, 2, 6, and 7. Local and systemic reactions were monitored by means of questionnaires. The results of our study demonstrate that the combined hepatitis A and B vaccine is well tolerated and highly immunogenic. The seropositivity and seroprotection rates were 100% for both antigens in all groups. Surprisingly, anti-HAV and anti-HBs antibody titres after the combined and mixed vaccines were significantly higher compared with the respective monovalent vaccines injected separately.

Interruption of an outbreak of hepatitis A in two villages by vaccination.

During a large community-wide outbreak of hepatitis A in two adjoining villages in Slovakia with a total of 5,000 inhabitants we administered to schoolchildren the first commercially available vaccine against hepatitis A (HAVRIX, Smith-Kline Beecham Biologicals, Rixensart, Belgium) in an attempt to control the progress of the epidemic. Soon after the start of the vaccination programme, an abrupt decrease in the occurrence of cases in the school was observed. In the village school with 624 schoolchildren, 404 had received a first dose of 360 enzyme-linked immunosorbent assay (ELISA) units (EL.U) and 373 a second dose 1 month later. Subsequent to the start of vaccination there were eight clinical cases of hepatitis A among the 157 children without a history of hepatitis A who remained unvaccinated and only 1 case in the vaccinated school children, giving attack rates of 5.1% and 0.25% in the two groups, respectively. Among the remaining 63 children, one was found seropositive when screened and 62 had a history of hepatitis A at the start of the vaccination programme. These 63 children were not offered vaccine. No cases occurred in that group. During the epidemic, three cases occurred an average of 20 days following its administration among 19 children who received immune globulin (IG). Cases in the whole population of the villages also ceased soon after the vaccination of the children had started. The vaccine was found more effective than postexposure IG in interrupting the epidemic in the whole community.

Review: protective efficacy of hepatitis B vaccines in neonates.

A literature search was carried out to investigate the factors that influence the protective efficacy (PE) of hepatitis B vaccines when given to neonates of hepatitis B surface antigen and e antigen positive mothers. Hepatitis B vaccines with either high or low antigen doses are very effective in preventing chronic hepatitis B infection in neonates at risk, but there is evidence that with lower dosages simultaneous use of hepatitis B immune globulin (HBIG) administration is more important than with higher dosages to elicit good protection (PE > or = 90%). There is also a tendency for lower dosages to confer high PE less consistently, with noticeably greater numbers of chronic surface antigen carriers in neonates who received a complete vaccination course. Furthermore vaccination courses with higher vaccine dosages give high PEs, without concomitant HBIG administration at birth, provided that the first vaccine dose is given at birth and that the second dose follows within 2 months.

Safety and immunogenicity of hepatitis A vaccine in healthy adult volunteers.

The immunogenicity and adverse reaction of an inactivated hepatitis A (HA) vaccine were investigated. Sixty healthy adult volunteers who lacked antibody to HA virus (anti-HAV) received three doses of vaccine containing 720 enzyme-linked immunosorbent assay (ELISA) units (EL.U) according to a 0, 1 and 6 month schedule. Blood tests for serum liver enzymes and anti-HAV were performed at screening 7 days prior to, and 1, 6 and 7 months after the first dose. Anti-HAV was tested by radio immunoassay and ELISA for titre determination. The seroconversion rates measured by ELISA were 98.3% (59/60) at months 1 and 6 and 100% at month 7. Sixty-one per cent (109/180) of the documented injections were followed by local symptoms, essentially mild soreness at the site of injection; and 22.2% (40/180) by minor general symptoms including malaise, fatigue and lethargy. It is concluded that HA vaccine is highly immunogenic and safe. It may replace immunoglobulin as an effective method of preventing HA virus infection in adults.