Development of Vaccines
Methods of developing new vaccines are highly variable, differing for each type of virus or bacteria. Animal experiments are usually required for selecting the initial materials in the formula, establishing the stability and formulation of the vaccine, and determining the mode and frequency of administration. Experimental vaccines are tested for safety and efficacy on animals before clinical tests on humans begin.

Production of Vaccines
Mice are the primary species of animal used in vaccine production. For example, in the Netherlands in 1986, roughly two-thirds of the experimental animals used to make biological products were mice. In the actual vaccine production process, only serum or blood of animals may be required for culturing media.

• Bacterial Vaccines
  For bacterial vaccines, serum or blood is sometimes required for culture media; this is the only use of animals in the production process.

• Virus Vaccines
  The production of a viral vaccine is broadly similar to that of a bacterial vaccine, involving seed lot, purification, concentration, and packaging, followed by freeze-drying. Viruses are propagated in cells of animal or human origin. In the past, viruses were cultured in vivo,as in the production of smallpox virus on the brains of mice. Since 1949, primary cell cultures have largely been produced using in vitro methods.

Quality Control
In vaccine production, mice are used most extensively for quality control. Vaccine formulations include constituents such as living tissues, viruses and bacteria. Thus, since all vaccine batches are not the same, their content and effects must be tested regularly at selected stages of production to monitor safety, as required by federal regulations.

Quality control is the most essential aspect of vaccine production. Human lives have been lost when quality control has not been sufficient. For example, thirteen children died in 1901 from tetanus, after receiving doses of diphtheria antitoxin which had been prepared from horse serum contaminated with the tetanus bacilli. In 1955, 79 cases of poliomyelitis occurred due to inadequate safety test procedures on polio vaccine; seven of the seventeen batches were later found to contain the living virus. The experimental animal is still the main indicator in the detection of desirable and undesirable activities of newly produced vaccine batches.

 

Safety Testing

Test for specific toxicity: Used to detect any incomplete inactivation of the vaccine product. Mice are injected with concentrated crude or purified product and observed for clinical symptoms.

Test for freedom from extraneous microorganisms: Used to detect inappropriate microorganisms such as viruses in the animal tissues used for production. Many can be detected by in vitro testing, but some still require animal testing. For human viral vaccines, intraperitoneal and intracerebral administration of vaccine to adult or newborn mice is used, with examination for clinical symptoms and/or specific antibodies in the blood serum.

Test for residual live virus: Used to detect live viruses. Cell culture is used in many cases. Rabies virus causes clinical symptoms or death in mice when administered intracerebrally.

Tumorigenicity test: Used to detect oncogenic properties in cells used for production of virus vaccines. Two groups of animals are used; the controls are injected subcutaneously with specific tumor cells, and the others are injected with cells from the production culture. The two groups are then compared for the development of tumors.

Safety test: Used to detect harmfulness. Multiple doses of the product are administered to two animals of the intended species, with observation for development of symptoms during a specified period.

Identity test: Used to verify that the product stimulates specific antibodies in an animal after immunization. Usually it is possible to use in vitro techniques. When it is necessary to use in vivo techniques, the specific antibodies must be demonstrated in the animal after immunization, either by challenging the animal with the virulent microorganism or by a serum-antibody assay.

Test for abnormal toxicity: Used to detect any unknown contamination of the vaccine from added chemicals. Either each of two guinea pigs gets five human doses, or each of 2 - 5 mice gets one human dose, and the animal is monitored for health and weight maintainance.

Potency Testing
Qualitative and quantitative assays are required to verify that the batch of vaccine induces protective immunity. In live, attenuated vaccine material, the numbers of live particles are determined by counting or by titration (an in vitro process). When a new seed strain is being used, a potency test is also conducted on animals.

For inactivated vaccine, each batch is tested in vivo, and the animals are monitored to assure that the vaccine has the efficacy expected in relation to its contents and, for example, that it is not weakening over time.

 

Vaccines for Animals and People
Vaccination to prevent disease is routine today for cattle, poultry, companion animals, and people. The knowledge gained from vaccination of animals helps improve human health, and vice versa. The typical human vaccine for tuberculosis, BCG, was derived from a related disease organism in cows. A new, experimental, genetically engineered TB vaccine uses isolated proteins from the BCG bacteria. Lacking live bacteria, this vaccine, if effective, would avoid risks and other shortcomings of the BCG vaccine. New developments are also underway in vaccines for malaria, chicken pox, whooping cough, and cancer.

Innovative Developments
Currently researchers are seeking to develop genetically altered plants that could provide immunity to infectious diseases. Studies have already shown that genetically engineered plants can act as a vaccine, causing an immunological response in mice that have eaten these plants. Plants acting as vaccines would offer the advantage of being inexpensive to produce, and thus they could more easily be made available to developing countries. In addition, contamination with animal viruses would be eliminated, since cultured cells would not be used in the production process. Many of the quality control tests that require animals also could be eliminated.
 

PRODUCTION SEQUENCE
Bacterial strain selected, stored longterm as "seed lot."

Working seed lot prepared and stored.

For a batch, microorganisms from working seed lot are cultured in serum or blood media.

Later, culture fluid is harvested for "crude vaccine bulk."

Purification, concentration, inactivation with formalin if not live vaccine.

"Purified bulk." add other components for final bulk vaccine that is packaged as doses and freeze-dried.

 

 

Lynette A. Hart, Professor, SVM:PHR
Amy Dassler, Undergraduate intern 1996
web contact

Return to Mouse in Science papers