Despite recent controversial opinions surrounding vaccinations, there is no doubt amongst the scientific and medical communities that the benefit of widespread immunization on global health is immense. However, one major challenge remaining in effectively spreading vaccination efforts to developing regions is transportation. Most vaccines contain components which are sensitive to temperature, and in many cases any exposure to temperatures above 2-8 ºC (around 35-46 ºF) can cause vaccines to lose their effectiveness. Thus, vaccines typically must be developed, stored, transported, and delivered while kept cold. This is known as maintaining the ‘cold chain,’ and it greatly increases the economic burden of global vaccination efforts. Heat-resistant vaccines for deadly diseases like measles, tetanus, and whooping cough are desperately needed in developing countries, including Nigeria, India, and Somalia.
Many current modifications that improve vaccines’ thermal stability rely on specialized technologies, such as freeze drying or spray drying, as dry vaccine materials are less sensitive to temperature. Now, researchers at McMaster University have developed a new cost-effective method for stabilizing vaccines for prolonged periods at elevated temperatures. The new stabilization technique draws from two common methods of improving thermal performance of vaccines: drying and adding stabilizing agents. However, in this method, the stabilization agents are already approved by the Food and Drug Administration (FDA) of the United States: two different kinds of sugar molecules called pullulan and trehalose. The vaccine material and the sugar solutions are simply mixed and left to dry overnight in a tube. Thus, no expensive specialized equipment is required, and the sugars are cheap and readily available.
The authors validated their technique on examples from two different classes of viruses- herpes simplex virus 2 (HSV-2), which contains infectious DNA, and influenza A virus (IAV), which instead uses the related but distinct RNA molecule. The vaccines for these viruses are constructed by using inactivated (killed) or attenuated (weakened) versions of the virus that produce the desired immune response, but they cannot cause infection. After initially confirming that their method was capable of preserving the infectivity of the live viruses themselves, they validated the ability to preserve vaccines by immunizing mice with the corresponding vaccines. Mice in groups of five were immunized with vaccines from four categories. The main experimental vaccines were preserved for an extended time (8 weeks for HSV-2 and 12 weeks for IAV) at elevated temperature (104 ºF) using the sugar-drying method. The efficacy of these vaccines were compared to vaccines stored at the same conditions but without sugar-drying, a control without any vaccine materials, and a fresh vaccine maintained using the cold chain. After sufficient time for immunization to take effect (2 weeks for HSV-2 and 30 days for IAV), the mice were exposed to a dose of the corresponding virus large enough to cause infection and death in non-immunized animals. In both cases, the sugar-dried vaccines performed as well as the vaccines from the cold chain, with all five mice from both groups either exhibiting no symptoms of infection at any point or recovering completely. For the control and non-stabilized vaccines, almost all mice died from the infection, and the one that did not for the IAV case still exhibited significant signs of infection.
These results are quite promising, as the two vaccines used in the experiment represent two broad categories of viruses and both are made from viruses that are notoriously difficult to stabilize. However, the amount of material present in the initial vaccine did show some initial rapid depletion which must be accounted for. There may also be unforeseen effects in trying to extend this method to other classes of vaccines. Even so, this simple and cheap method is a significant step forward in addressing one of the remaining challenges facing an essential component of improving global health.
Managing Correspondent: Andrew T. Sullivan
Press Articles: Canadian scientists figure out how to preserve vaccines without refrigeration – a potential public-health game changer, National Post
Original Journal Article: “Thermal Stabilization of Viral Vaccines in Low-Cost Sugar Films,” Nature Scientific Reports
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