Chickenpox is the most widely known viral infection caused by the highly contagious varicella-zoster virus (VZV). VZV is a member of the herpes virus group, remaining dormant in the body after initial infection and with the potential to cause a latent infection later in life. VZV remains in the dorsal root of sensory nerve ganglia and can result in a recurrent infection known as shingles. The symptoms of shingles include a skin rash, blisters and pain, which may be prolonged.
The current solution
The viruses within the VZV vaccine are fragile and must be handled carefully. To maintain potency, the freeze-dried vaccine must be handled according to the package insert and kept at pre-defined temperatures, often as low as -50°C, until it is reconstituted for injection. The diluent is stored separately at room temperature or in the refrigerator and once reconstituted the vaccine is discarded if it is not used within a strict time frame, sometimes as low as 30 minutes.
Vaccine efficacy losses
As soon as the vaccine is released from the cell culture, viral integrity begins to decline, resulting in a reducing titre. There are several key points during production where losses frequently occur. Prevention at any of these points will have significant effects on the vaccine yield:
Fill/Finish – the bulk vaccine can be exposed to less than optimal temperatures for the duration of the fill run
Lyophilisation losses – the lyophilisation process is a highly destructive process for many biologically active products, unless measures are taken, typically by formulation, to offset and prevent this damage.
Distribution – A large portion of vaccine integrity/efficacy can be lost during distribution due to temperature excursions during transit.
Developing the next generation VZV vaccine
Through our THERM-SB technology, we are addressing the issues of thermostability and lyophilisation damage in VZV vaccine development, with the aim to increase yields, increase efficacy and lower manufacturing costs. In this project, we have used the OKA vaccine strain to develop a vaccine that is stable at room temperature for several hours with minimal loss of titre. The vaccine also shows lower losses through lyophilisation than any other published results. Once dried, the virus demonstrates enhanced stability with minimal losses observed over seven weeks at 25°C.