Anti-Viral Vaccines

Killed (inactivated) vaccines

• When safe live vaccines are not available, either because attenuated strains have not been developed or else because reversion to wild type occurs too readily, it may be possible to use an inactivated  preparation of the virulent organism to immunize the host.
• The organism is propagated in bulk, in vitro, and inactivated with either beta-propiolactone or formaldehyde. These vaccines are not infectious and are therefore relatively safe. However, they are usually of lower immunogenicity and multiple doses may be needed to induce immunity. In addition, they are usually expensive to prepare.
• Subcellular fractions
• When protective immunity is known to be directed against only one or two proteins of an organism, it may be possible to use a purified preparation of these proteins as a vaccine. The organism is grown in bulk and inactivated, and then the protein of interest is purified and concentrated from the culture suspension. These vaccines are safe and fewer local reactions occur at the injection site. However, the same disadvantages of poor immunogenicity and the need for multiple boosters applies.
• Recombinant proteins
• Immunogenic proteins of virulent organisms may be synthesized artificially by introducing the gene coding for the protein into an expression vector, such as E-coli or yeasts. The protein of interest can be extracted from lysates of the expression vector, then concentrated and purified for use as a vaccine. The only example of such a vaccine, in current use, is the hepatitis B vaccine.

Killed (inactivated) vaccines

• Attributes
• Immune response
• poor; only antibody - no cell immediated immune response.
• response is short-lived and multiple doses are needed.
• may be enhanced by the incorporation of adjuvants into the vaccine preparation (see below)
• 1. Safety
• Inactivated, therefore cannot replicate in the host and cause disease.
• Local reactions at the site of injection may occur.
• 2. Stability
• Efficacy of the vaccine does not rely on the viability of the organisms.
• These vaccines tend to be able to withstand more adverse storage conditions.
• 3. Expense
• Expensive to prepare