Vaccines are the most cost-effective and efficient means of preventing and controlling infectious diseases, and vaccination is a routine method of preventing and controlling human and animal diseases by inducing a protective immune response in the body. Although highly effective, vaccines still present some challenges in their production and use:

① Structural instability;

② Easily destroyed by enzymes prevalent in the environment

③ Need to be stored between -20℃ and -70℃.

This means that vaccines need frozen storage and cold chain transportation throughout, and distribution and use can become very difficult, and these challenges can be solved by vacuum freeze drying. Currently, freeze drying technology has been widely used in vaccines, antibodies and other biopharmaceuticals due to its unique advantages.

Vaccines use pathogenic microorganisms by means of substitution or genetic modification, without destroying the original immunogenicity on the basis of the pathogenic microorganisms without pathogenicity, the pathogenic microorganisms that have lost their pathogenicity will be put into the lyophilizer after amplification of the culture solution. After low temperature and reduced vacuum, the water in the culture solution is separated by sublimation, and the dry powder that maintains the immunogenicity of the original microorganism is made, which is the lyophilized vaccine.

Freeze-drying technology is the key technology in the preparation process of vaccines in freeze-dried dosage form. In the process of vaccine freeze-drying and storage, the chemical composition of the vaccine, the freezing temperature and rate, the drying temperature and residual moisture in the dried solids, and the temperature and humidity of the storage environment will all have an impact on the vaccine's activity, and thus the vaccine will be affected, and thus the vaccine needs to be optimized by freeze-drying process.

1. Freezing and drying have an effect on vaccine characteristics and hence on vaccine stability. Slow freezing leads to the formation of a small number of large crystals, which may be harmful to the vaccine; whereas fast freezing reduces the time for osmotic water release, but creates a greater risk of internal icing. The choice between fast or slow freezing is therefore difficult, so considering the freezing rate during vaccine lyophilization development is critical to vaccine stability.

2. Product temperature is critical throughout the sublimation drying step, affecting drying time, sublimation rate and stability. When optimizing the main drying parameters for vaccine lyophilization, it is worth considering the cost efficiency of reducing drying time and product stability.

3. Removal of moisture during resolution drying reduces product stability, and high residual moisture can lead to collapse, aggregation and degradation. Therefore, optimal residual moisture content and resolution drying conditions should also be part of the lyophilization process for vaccine development.   

4. Cryoprotectants in the development and production of vaccine freeze-drying plays a key role in the amorphous cryoprotectants such as sugar alcohols and sugars, in the freezing process by prioritizing the exclusion of cryoprotectants and proteins hydration in the thermodynamic stability.

In summary, freeze-drying is an ideal technology for improving vaccine stability. The process requirements for freeze-drying should be explored in vaccine freeze-drying research and development and production to prevent any damage to the vaccine and to maintain its long-term stability.