New method makes vaccines stable at tropical temperatures
18 February 2010
Infectious diseases kill millions of people every year in low-income countries but many of these deaths could be avoided by vaccination.
"Currently vaccines need to be stored in a fridge or freezer," explains Dr Matt Cottingham of the Jenner Institute at the University of Oxford, who led the research. "That means you need a clinic with a nurse, a fridge and an electricity supply, and refrigeration lorries for distribution."
"If you could ship vaccines at normal temperatures, you would greatly reduce cost and hugely improve access to vaccines," he says. "You could even picture someone with a backpack taking vaccine doses on a bike into remote villages."
In the proof-of-concept study, the team of researchers from Oxford and Nova Bio-Pharma Technologies showed it was possible to store two different virus-based vaccines for up to six months at 45°C without any degradation. The vaccines could be kept for a year and more at 37°C, with only tiny losses in the amount of viral vaccine.
The work, funded by the Grand Challenges in Global Health partnership with other funds from the Wellcome Trust, is published in the journal 'Science Translational Medicine'.
"We've developed a very simple way of heat-stabilising vaccines and shown it works for two viruses that are being used as the basis for novel vaccines in development," says principal investigator Professor Adrian Hill of the University of Oxford. "This is so exciting scientifically because these viruses are fragile. If we are able to stabilise these, other vaccines are likely to be easier."
The team's method involves mixing the vaccine with the sugars trehalose and sucrose. The mixture is then left to slowly dry out on a simple filter or membrane. As it dries and the water evaporates the vaccine mixture turns into a syrup and then fully solidifies on the membrane.
The thin sugary film that forms on the membrane preserves the active part of the vaccine in a kind of suspended animation, protected from degradation even at high temperature. Flushing the membrane with water rehydrates the vaccine from the membrane in an instant.
"The beauty of this approach is that a simple plastic cartridge, containing the membrane with vaccine dried on, can be placed on the end of a syringe," explains Dr Cottingham. "Pushing a liquid solution from the syringe over the membrane would then release the vaccine and inject it into the patient."
The process could be used for many types of vaccines and sensitive biological agents. The next steps are to show that it can be scaled up to industrial manufacturing levels and also to demonstrate that it works with a standard or newly licensed human vaccine.
Professor Hill added: "The World Health Organization's immunisation programme vaccinates nearly 80 per cent of the children born today against six killer diseases: polio, diphtheria, tuberculosis, whooping cough, measles and tetanus. One of the biggest costs is maintaining what's called the cold chain - making sure vaccines are refrigerated all the way from the manufacturer to the child, whether they are in the Western world or the remotest village in Africa. If most or all of the vaccines could be stabilised at high temperatures, it would not only remove cost, more children would be vaccinated."
Image: Papua New Guinea; infant vaccination against infectious diseases given by nurse in a clinic while the mother holds her child. Credit: Wellcome Images
Reference
Alcock R et al. Long-term thermostabilisation of live poxviral and adenoviral vaccine vectors at supraphysiological temperatures in carbohydrate glass. Sci Transl Med 2010 [Epub ahead of print].
