As vaccines are undoubtedly classified as drugs, they must undergo a rigorous preclinical toxicity assessment. This assessment should be adequate to identify and characterize potential toxic effects of a vaccine to allow investigators to conclude that it is reasonably safe to proceed to clinical investigation.
Potential toxicity in vaccines
During the development of vaccines, several safety issues may arise, most of which stem from the following types of toxic effects.
- Intrinsic toxicity of the test article (i.e., caused directly by the vaccine component(s) per se). For vaccines, this type of toxic effect should be very rare given the small amount of antigen in the human dose and the limited number of doses administered. Intrinsic toxicity related to adjuvants, excipients or preservatives in the final formulation must be evaluated for toxicity.
- Toxicity linked to the pharmacodynamic activity of the candidate vaccine or its components (e.g., cross-reactivity between autoantigens and vaccine-produced antibodies). The assessment of such toxic effects is more complex than intrinsic toxicity and requires careful selection of the relevant animal species.
- Toxicity caused by contaminants and residual impurities. The absence of contaminants and impurities is a fundamental criterion for products such as vaccines, where one of the main objectives is to remove all substances of animal origin in order to avoid the risk of introducing foreign substances. The control of such toxicity is also the main purpose of quality control studies.
- Potential toxic reactions due to interactions between various vaccine components. This type of potential toxicity assessment is critical for the development of a combination vaccine (a polyvalent vaccine that contains several antigens in a single preparation to protect against multiple diseases).
Animal models for vaccine toxicity assessment
When conducting vaccine toxicity assessments, studies are often conducted using animal models. Several factors to be considered in the study include: the relevance of the animal model, the sensitivity of the model to detect immune-mediated effects or intrinsic toxicity, the value of specific species historical control databases, and the consistency of effects with clinical safety data. The health of the animal will need to be evaluated in accordance with acceptable veterinary medical practice to ensure that animals are free of any condition that might interfere with the study. For instance, individual housing of laboratory animals may be required to minimize the risk of cross-infection. In general, one relevant animal species is sufficient for use in toxicity studies to support initiation of clinical trials. However, there may be situations in which two or more species may be necessary to characterize the product, for example where the mechanism of protection induced by the vaccine is not well understood. The most widely used species for vaccine Good Laboratory Practices (GLP) toxicity investigations are rats, rabbits, mice, and non-human primates.
Our toxicity assessment services include but are not limited to the following.
- Evaluate the initial safe dose and subsequent dose escalation schemes.
- Evaluate single and repeat dosage, establish a set of safety parameters.
- Demonstrate potential reversibility of virulence.
- Demonstrate the level of inactivation of the vaccine strains.
- Evaluate the potential of the vaccine antigens to cause the release of antibodies that are cross-reactive with human tissues.
- Evaluate the effect of the vaccine on reproduction and development.
Why choose us
By utilizing our experienced experts to work with your team, Alfa Chemistry helps you gain a wide range of information from your toxicity studies. If you have any questions related to toxicity assessment, please feel free to contact us. Alfa Chemistry is always your project partner.
Our products and services are for research use only and cannot be used for any clinical purposes.