Vaccines: a step towards thermostability

Ensilication of the protein molecules of a vaccine against tuberculosis prevents its deterioration by heat.

“A lack of infrastructure, equipment and effective logistics required to support this cold chain, particularly in developing countries, can lead to 75–100% of vaccines being exposed to suboptimal temperatures during dissemination. As a consequence, up to 50% of manufactured vaccines are discarded before administration.”

An article published by a team of researchers of the University of Bath begins with these terms. It was published last August in Nature – Scientific Reports. These figures were published in the Journal of Pharmaceutical Sciences [1] and in Current Opinion in Biotechnology [2].

To avoid those losses, the team of scientists sought solutions that would help keep vaccines out of the 2 to 8 °C temperature range, as recommended by WHO.

Different techniques have been experimented for several years:

- Lyophilisation is commonly used, but requires the use of protective agents and stabilizing agents. This increases the cost of vaccination, and the freezing and drying used in this method do not make it suitable for vaccines, composed mainly of individual proteins

- Spray drying or vacuum-foam drying

- The use of membranes stabilized with sugar.

- Ensilication

This latter method was developed by the University of Bath team. It has been tested on a vaccine against tuberculosis.

It is composed of Sbi adjuvant proteins and the Ag85b antigen of tuberculosis. The process involves shrinking the vaccine proteins with layers of silicas that accumulate in a cage around the molecules. Thus, they remain intact when exposed to temperatures that would usually decompose them. The proteins are held in place until they can be removed from the silica cage and delivered.

According to the experiments conducted by the team, this vaccine can be stored for long periods at room temperature (a sample was thus stored for 7 months at 21 °C without showing signs of degradation).

[1] Brandau, D., Jones, L., Wiethoff, C., Rexroad, J. & Middaugh, C. Thermal stability of vaccines. Journal of Pharmaceutical Sciences 92, 218–231,

[2] Hill, A., Kilgore, C., McGlynn, M. & Jones, C. Improving global vaccine accessibility. Current Opinion in Biotechnology 42, 67–73, (2016).