Drying environment is the basis of stability for the Newcastle disease vaccine derived from the La Sota and BOR-74 strains

Outbreaks of such a highly contagious viral disease as the Newcastle disease cause severe economic damage and permanently paralyze work of farms suffering from the disease. Live lyophilized vaccines derived from the LaSota and Bor-74 strains efficiently prevent the Newcastle disease.

Our forty year experience of producing and applying such vaccines demonstrated the importance of maintaining their activity and solubility until they are used. In this regard, vaccine stabilizer plays a crucial role as it protects the virus material against inactivation during freeze-drying (lyophilization) and storage.

Previously Shchelkovo Biocombinat used only freeze drying base of skim milk that provides good stabilizing and antioxidant effects. However, use of such medium without amino acids - non peptide and carbohydrate components, might bring about undesired effects caused by difficult standardization of skim milk prone to contamination of external microflora during its preparation.

To prevent potential negative effect of skim milk on the vaccine quality we considered the proposal of VNIITIBP research facility and improved drying media by including  lactose peptone stabilizer based on potassium phosphate buffer. We also considered that according to general requirements drying media must:

• remain nonreactive relative to chemical characteristics of the product and support preservation of its bioactivity in a liquid or dried form;
• be harmless for vaccinated bodies;
• keep the dried product inside the vial during dry freezing and prevent its evaporation together with sublimated water vapor;
• Provide product’s  high potency up within its shelf life.

As water maintains natural spatial structure of biomolecules its removal requires replacing water molecules with molecules of other substances that are able to preserve structure and subsequent revitalization of vaccine virus, stabilize spatial structure of biomolecules and retain liquid form at low temperatures. 

This can be done by using an optimal proportion of carbohydrates with low molecular weight (for example, lactose) and di or tripeptides, potassium ions and phosphate ions. Together they create supercooled liquid membrane in the glassy state, which in contact with the hydrophilic portions of biomolecules forms an elastic web of ionic and hydrogen bonds.

Compared to skim milk peptone received by acid or enzymic hydrolysis (or by optimal combination of these two methods) contains aminoacids, di or tripeptides in higher molar fractions, therefore it has better colligative properties that are more  effective during dry freezing.

In particular, it considerably decreases freezing temperature for water-based systems. By fixing conditions of protein hydrolysis  it is possible to make a more accurate peptone adjustment.  At the same time carbohydrate in its pure form can be added to the medium in the needed quantity. This method improved drying media, as it helps to pick out optimal concentrations of peptone and lactose, not exceeding 10% for both substances.

After revising  its norms and specifications  Shchelkovo Biocombinat  started using not only skim milk but also modified drying medium with lactose peptone stabilizer based on potassium phosphate buffer.

It has been established that formulations made with a combined medium, provide a required level of immunogenic activity during an entire storage period. Data measuring potency of the virus vaccine that prevents Newcastle disease among poultry and is made of La Sota strain were received from vaccine with lifetime less than 12 months. Similar results were received when using the aforementioned vaccine stabilizer.

Verification of several vaccine series proved that the form of freeze-dried mass of the formulation does not affect the vaccine potency.

Therefore, combined dried medium helps to protect dried lyophilized virus vaccines  used to prevent Newcastle disease and made from Bor 74 and La Sota strains from the entire spectrum of negative effects during freeze-drying  and storage. At the same time the media provides a good solubility of the formulation  in water given to chickens.