Vaccines are vital to maintaining public health, however there are still many parts of the world without proper access to life-saving immunization. Global distribution is complicated by the “cold chain” — a constant network of refrigeration during transport and storage. The cold chain is necessary, but not always feasible in areas with low resources.
Proteins within vaccines will begin to degrade when exposed to temperatures outside the range of 36 to 46 degrees Fahrenheit. When the proteins degrade, the vaccine loses its ability to immunize a patient, so finding a way to ensure thermal stability is a serious pursuit for global health.
A new paper by researchers from the University of Bath’s Chemistry and Biochemistry departments in collaboration with scientists from the University of Newcastle shows how a method called “ensilication” poses a solution to the problem.
To ensilicate a molecule, scientists deposit a network of silica, a chemical found naturally as a constituent of sand, around it. Silica recognizes the shape of the protein and then matches it, forming a “cage” like structure. This cage prevents the vaccine protein from degrading through the denaturation process. When a protein denatures, it loses its structure and unfolds. The shape and folding of a protein is essential to function, which is why unfolding impacts the ability of a vaccine to immunize.
However, with ensilication, the silica coating helps the protein maintain its shape and prevents denaturation.
Last year, the Bath Chemistry and Biochemistry researchers demonstrated the ensilication method improved the thermal stability of the tuberculosis antigen 85b, which is an important component of the tuberculosis vaccine. They also ensilicated the vaccine adjuvant Sbi III-IV, which promotes a strong immune response to the antigen.
Other efforts to make vaccines thermally stable include employing freeze-drying. Once transported, the freeze-dried proteins are then re-added to liquid before injection. Still, not all proteins can survive the freeze-drying process.
For their new study, the researchers ensilicated the tetanus toxin C fragment (TTCF), a component of the Diphtheria Tetanus Pertussis (DTP) vaccine.
According to UNICEF, the DTP vaccine is often used to determine how well a country is providing immunization services. While data from the World Health Organization shows DTP was administered to 86 percent of the global population of one year olds in 2018, in some countries, including South Sudan and Somalia, the figure was less than 50 percent, so there is still progress to be made in ensuring the vaccine is available to everyone.
Once ensilicated, the researchers then exposed the proteins to a number of unfavorable conditions, including 212 degree Fahrenheit heat and allowed it to age for up to six months at room temperature.
They found the ensilicated TTCF withstood the heating and remained functional once released back into a solution.
The researchers hope the process of ensilication will eliminate the need for the cold chain and improve vaccine access worldwide.