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[Live vaccines for the prevention of intestinal infections]
Insights
Oral Shigella vaccines showed limited efficacy in children, with higher morbidity post-immunization. However, animal studies suggest potential for developing effective combination vaccines against Shigella and Salmonella infections.
Area of Science:
- Microbiology
- Immunology
- Vaccinology
Background:
- Shigella infections pose a significant public health challenge, particularly in children.
- Development of effective vaccines against Shigella is crucial for disease prevention.
Purpose of the Study:
- To evaluate the efficacy of an oral Shigella live vaccine in children.
- To explore the potential of developing novel combination vaccines using bacterial mutants.
Main Methods:
- Oral administration of a Shigella live vaccine to 12,000 children aged 1-7 years.
- Monitoring morbidity rates in vaccinated versus control groups.
- Conducting animal experiments, including pulmonary and kerato-conjunctival tests on mice, using Shigella and Salmonella antigens.
Main Results:
- The oral Shigella vaccine showed increased morbidity (3.5x, 9.3x after boosting) compared to controls.
- Induced immunity was short-lived (4 months) and type-specific.
- Oral immunization of mice with Salmonella typhimurium antigen provided significant protection against lethal challenge.
Conclusions:
- The tested oral Shigella vaccine demonstrated limited clinical efficacy and short-term, type-specific immunity in children.
- Animal model results support the development of combination vaccines using streptomycin-dependent Shigella mutants (S. flexnerica, S. sonnei) and Salmonella mutants (S. enteritidis, S. typhimurium).
- Further research on bacterial mutants is expected to lay the foundation for effective vaccine design.
Abstract:
Shigella live vaccine was applied orally, four or five times, to 12000 children, aged between one and seven years. Morbidity in the immunised group was 3.5 times as high (9.3 times after boostering) as that in the non-immunised control group. Immunity could be provided for four months, and it was strictly specific of types. Results so far obtained from animal experiments, such as pulmonary and kerato-conjunctival tests on mice, are likely to support the idea of developing a combination vaccine from streptomycin-dependent Sh. flexnerica and Sh. sonnei mutants. Oral immunisation of mice, using 0.25 mg of dissolved Salmonella (S.) typhimurium antigen provided protection for all animals that had been exposed to 150 times of LD50, while 70 per cent of the mice involved still were protected by one tenth of that dose. More mutants will be tested (Shigella; S. enteritidis; S. typhimurium), and the expected results may give a foundation on which to devise effective vaccines.