Scientists have developed three simple and inexpensive additives to stabilise vaccines at room temperature for a long time, an advance that will allow shipping them to remote areas and developing countries.
Researchers from Supramolecular Nanomaterials and Interfaces Laboratory (SUNMIL) in Switzerland were able to achieve this by using minute quantities of nanoparticles polyethylene glycol polymer or higher amounts of sucrose.
The study addressed viral-vector vaccines, the most common type of vaccine, which normally only last for a few days at room temperature.
At that point, the viral components of the vaccines lose their structural integrity.
"These components fluctuate by their very nature. They are combined in a stable form, and the low temperature maintains that balance," said Francesco Stellacci from SUNMIL.
"However the thermally induced fluctuations eventually lead to a loss of integrity of the viral vector," he said.
The approach, which consists of stabilising the vaccines against such fluctuations through simple biocompatible additives, has delivered excellent results.
In their first approach, osmotic pressure is applied on the inactivated viruses (the main component of the vaccine) using a cloud of negatively charged nanoparticles.
The virus is already subject to an outward osmotic pressure due to its genetic material (RNA or DNA), which has a high negative charge and is held inside the virus.
The nanoparticles form a cloud of negatively charged objects that cannot enter the virus, thus generating counter-osmotic pressure that keeps the virus intact.
"With this method, infectivity for a virus reached a half-life of 20 days," said Stellacci.
The second approach consists in stiffening the virus's capsid, which envelops the inactivated virus, by adding polymers.
This additive mainly stabilises the virus by slowing its oscillations by changing the stiffness of the capsid. As a result, the vaccine remained fully intact for 20 days with an estimated half-life of around 70 days.
Finally, adding sucrose, a common sugar, to the vaccine makes the environment more viscous and slows down fluctuations.
"It is a little like adding honey, where all motion is slowed down," said Stellacci.
With this third approach, 85 per cent of the vaccine's properties were intact after 70 days.
Using these results, the researchers applied their methods to a vaccine that is currently in development. They were able to stabilise a vaccine against Chikungunya, a tropical virus, for 10 days, and then successfully inoculated mice with it.
The study was published in the journal Nature Communications.
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