Un vaccin expérimental contre Ebola en République Démocratique du Congo (en anglais)
On May 8, 2018, the Democratic Republic of the Congo's health minister declared an outbreak of Ebola.
In order to stop or at least to contain the propagation of the virus, a vaccination campaign was launched a few weeks later. By June 1, more than 680 people had received Ebola vaccinations in the three health zones where dozens of cases of the deadly virus had been confirmed. According to the World Health Organization (WHO), more than 1,700 doses of the rVSV-ZEBOV Ebola vaccine have been sent to the Democratic Republic of the Congo to be used in a vaccination campaign in the northwestern Equator Province.
The vaccine, developed by Merck, is still experimental. Though it is promising, there are serious obstacles to the distribution of the vaccine. Health workers, who are vaccinated themselves, have to identify and track down anyone who has had contact with a sick person, and the vaccines must be transported across the country in difficult conditions and high temperatures.
One of the particularities of the Ebola vaccine is its storage temperature. Unlike most vaccines, which have to be stored between +2 °C and +8 °C, the Ebola vaccine needs to be stored at a temperature of -60 °C to -80 °C. WHO has sent special vaccine carriers which can keep their contents at sub-zero temperatures for up to a week, and has set up freezers in which to store the inocula in Mbandaka and Bikoro.
During the first trial of the vaccine in Guinea in 2015, Intellectual Ventures Lab and their commercial Chinese partner Aucma developed "modified passive vaccine storage devices" called Arkteks to transport the vaccines. The original version of the Arktek employed insulation techniques similar to those used to store cryogenic fluids and protect spacecraft from extreme temperatures. Once stocked with water ice, the device is able to keep inocula between + 2°C and +8°C for months or more, without external power.
To keep Ebola vaccines between -60°C and -80°C in a climate where external temperatures can reach +43°C, a team of researchers identified a proprietary phase change material (PCM) based on a denatured alcohol, made by a small company in England. The original Arktek devices were made of polyethylene but this proved incompatible with the PCM. The polyethylene was then replaced by aluminium.
The tests showed that this new device was able to keep vaccines cold inside the Arktek for over six days. Dry ice is another solution, but the substance was not available in Guinea during the trials. The devices are also equipped with a monitoring system: a notification sent by SMS indicates if the vaccines are nearing the temperature range recommended by Strategic Advisory Group of Experts (SAGE) of the World Health Organization.
According to Mike Friend, principal investigator at Intellectual Ventures, one of the big challenges is that all the mechanisms of heat transfer between the warm exterior and the cold interior have to be reduced. A vacuum reduces convection. A shiny coating on the inner vessel cuts down thermal radiation. The low conduction of the reinforced fiberglass keeps heat from leaking.
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