Cholera vaccines

29. Immunization

The medical dictionary defines immunization as the "protection of susceptible individuals from communicable diseases by the administration of a living modified agent, a suspension of killed organisms, or an inactivated toxin." This elegant description can be expanded to include twenty-first century approaches to immunization that include recombinant technology, reassortment virus techniques, live vectors, DNA vaccines, and the expansion of the field to encompass noncommunicable diseases such as Alzheimer's disease, autoimmunity, and tumor immunogenetics. Integral to the success of immunization is our knowledge of the immune system's memory of antigens, yet our understanding of this fundamental feature remains limited. On a global scale, communicable diseases remain the number-one cause of morbidity and mortality; hence Jenner's pioneering work with its birth in 1796 still has a challenging and exciting future.

Immunizations for international travel

Many infections encountered by international travelers can be prevented by adherence to personal protective measures and appropriate vaccinations. This review outlined the incidence and importance of the major vaccine-preventable infectious diseases encountered by U.S. travelers, as well as the indications, contraindications, and side effects of available vaccines. Official proof of yellow fever vaccine often is required for entry into some countries. Based on endemic or epidemic infections at destinations, planned activities, and age and medical history of international travelers, other vaccines may be recommended. Many clinicians will be familiar with some of the infections and vaccines that may be used in travelers; other vaccines may be encountered infrequently and associated with significant risk of adverse effects. Since vaccines do not provide complete protection and some travel-related infections do not have vaccines available yet (e.g., malaria and dengue fever), physicians need to be vigilant concerning febrile illness in returning travelers.

Efficacy of atovaquone/proguanil for malaria prophylaxis in children and its effect on the immunogenicity of live oral typhoid and cholera vaccines

A double-blind, placebo-controlled study was conducted to measure the impact of malaria prophylaxis with atovaquone/proguanil (A-P) on the immunogenicity of vaccines against typhoid fever and cholera, Salmonella serotype Typhi Ty21a and Vibrio cholerae CVD103-HgR, respectively. A total of 330 Gabonese schoolchildren were assigned to receive either A-P or placebo for 12 weeks. Vaccination occurred 3 weeks after the start of prophylaxis, and immunogenicity was assessed 4 weeks after vaccination. The protective efficacy of A-P against Plasmodium falciparum malaria was of 97% (95% confidence interval, 79%-100%). The 2 treatment groups did not differ significantly with regard to changes in antibody titers after vaccination (P=.96 for anti-S. Typhi IgG antibodies, P=.07 for anti-S. Typhi IgA antibodies, and P=.64 for vibriocidal antibodies). The A-P combination was highly effective for malaria prophylaxis, without interfering with the in vivo immunogenicity of CVD103-HgR and Ty21a vaccines, and it could therefore be simultaneously administered with these vaccines.

Endemic infectious diseases of Afghanistan

The current crisis in Afghanistan has resulted in an influx of Western military personnel, peacekeepers, humanitarian workers, and journalists. At the same time, unprecedented numbers of internally displaced persons and refugees have overwhelmed much of the already fragile infrastructure, setting the stage for outbreaks of infectious diseases among both foreigners and local populations. This review surveys the literature concerning the infectious diseases of Afghanistan and south-central Asia, with particular emphasis on diseases not typically seen in the Western world.

Update on Traveler's Diarrhea

Diarrhea is one of the most common health problems among travelers. Although enterotoxigenic Escherichia coli is implicated most commonly, enteroaggregative E. coli has recently been described as a major pathogen. Shigella, Campylobacter, and Salmonella organisms are less common causes of acute diarrhea, and intestinal protozoa are typical causes of protracted diarrhea. Although education is the mainstay of prevention measures, behavior modification has been shown to be difficult. Chemoprevention is rarely required with the availability of effective treatment, but there has been some interest in the use of vaccines. Maintenance of hydration is most important in children. In addition to bismuth preparations and loperamide, newer agents being developed for symptomatic relief include zaldaride maleate and racecadotril. Fluoroquinolones effectively treat severe traveler's diarrhea, and even a single dose may be sufficient. However, with the emergence of resistance, particularly in Campylobacter infection, other agents are required; interest has focused on azithromycin and rifaximin.

Recent developments in cholera

Cholera continues to be an important public health problem among many poorer communities in Africa, Asia and South America, despite the bacteriology and epidemiology of the disease having been described over a century ago. Molecular techniques have enabled current researchers to gain new insights into pathogenicity, into the relationships between environmental and clinical strains, and into new strategies for vaccine development. The description of non-culturable 'dormant' strains in the environment and the effect of environmental factors on toxin gene regulation provide valuable clues to the ecology of the disease. Disease management continues to be based on urgent and appropriate rehydration, and recent community studies emphasize the need for effective local health services to provide this if case fatality rates are to remain low. While antimicrobial agents may play a role in case management and prophylaxis, the increasing prevalence of antimicrobial resistance must be addressed. New vaccine candidates, based on a molecular understanding of pathogenicity, provide scope for improved strategies for disease prevention, though the appropriate public health context for their use has not been determined. This review summarizes activities in these fields of cholera research and considers the continuing global problem of the disease.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.

New developments in the understanding of cholera

Recent advances in prevention and treatment of cholera have occurred in the areas of vaccine testing, modifications of oral-rehydration solutions (ORS), and antimicrobial treatment. Oral vaccines consisting of killed whole bacterial cells (WC) with and without the B-subunit of cholera toxin (BS) were shown to be effective in large trials in Bangladesh, Peru, and Vietnam. However, the trials did not resolve whether two or three doses of vaccine are required and whether BS adds significantly to the immune protection of WC. Live, attenuated bacterial vaccines that are immunogenic and have been shown protective in human volunteer studies are candidates for future field trials. Rehydration of patients is a life- saving effort. The best ORS contains rice powder in place of glucose, and solutions with reduced osmolarity (245 mOsm/L, sodium 75 mEq/L) are as effective as standard ORS. Ciprofloxacin in a single dose is effective in adults, and erythromycin or ampicillin in multiple doses is effective in children.