The refrigerators known as "solar direct-drive" have contributed to a 50% increase in child vaccinations in the poorest rural provinces of the DRC over the past year, as reported by global vaccine alliance Gavi. This has resulted in a significant reduction in child mortality rates in the DRC compared to two decades ago. Last year, more than 18 million children were vaccinated against a deadly measles outbreak, which has since slowed down. With the hope of launching a larger immunisation effort once COVID-19 vaccines are available, the world faces the challenge of delivering millions of inoculations in Africa, a continent with weak health systems and limited access to electricity. It is uncertain whether current off-grid refrigerators can maintain the necessary cold temperatures for storing vaccines effectively. Refrigeration is crucial for the distribution of vaccines, as many require temperatures between 2 and 8 degrees Celsius (35-46 degrees Fahrenheit). However, nearly half of the leading COVID-19 vaccine candidates being developed may need storage as low as minus 80C. A distribution network for COVID-19 vaccines will need to maintain consistently low temperatures from manufacturers to remote rural areas. Although advances have improved vaccination storage in recent years, many African countries still lack adequate cold chain networks. According to Toby Peters, a professor at the University of Birmingham specializing in cooling systems for food and medicine, the logistical challenge of providing refrigeration for vaccines in sub-Saharan African countries, particularly those with rural populations, is perhaps the greatest challenge the world has ever faced. In the past, outdated kerosene-powered refrigerators caused issues with vaccine storage in health centers. However, the introduction of solar direct-drive refrigerators about a decade ago has revolutionized vaccine storage by directly connecting to solar panels, allowing for reliable cooling without the need for storage batteries that often fail after a few years. These refrigerators, which cost between $3,500 and $9,000, use thermal energy to keep vaccines cool for many days regardless of the weather. In 2016, only 16% of rural health centers in the DRC had functioning refrigerators, but today nearly 80% have been equipped, many with direct-drive solar units. This has led to a significant increase in immunization sessions, with 24,000 being held monthly in the poorest provinces, a 50% increase from 2018. According to Clemmer, this has transformed vaccine delivery for children in sub-Saharan Africa. Karan Sagar, a doctor at Gavi, attributes a 25% rise in child vaccination rates in Africa over the past decade to the use of off-grid equipment. Since 2017, Gavi has led a $250-million initiative to distribute over 15,300 solar direct-drive fridges to various African countries. Nearly 3,400 fridges were sent to the DRC and 5,400 to Nigeria. Last year, 87% of children in these countries received the first dose of a vaccine for diphtheria, tetanus, and pertussis, showcasing the effectiveness of supply chains in reaching remote communities. Moving vaccines from manufacturing sites to urban and rural areas in Africa will require several steps, including the use of solar refrigerators. Throughout the entire process – from transportation by airplanes, warehouses, trucks, motorbikes, bicycles, canoes, and even drones – the vaccines must be maintained at specific, very low temperatures, similar to other perishable items. The COVID-19 vaccine will require significantly larger quantities, with health experts estimating a need to reach up to 750 million people in Africa alone, compared to the typical 115 million infants reached in annual child vaccination campaigns worldwide. In preparation for this task, cold chain expert Peters is spearheading a government-supported initiative to assess Africa's requirements for distributing the COVID-19 vaccine, collaborating with nonprofit organizations, businesses, and academic institutions. They are leveraging insights from Rwanda, a country in central-east Africa that has made notable advancements in establishing efficient, environmentally-friendly cold chains for food and vaccine distribution. The system is centered around a single warehouse that functions as a cooling center for vaccines distributed to various medical facilities in Rwanda. Many of these facilities, including remote rural health posts, use solar fridges. The World Health Organization states that these vaccines are reaching over 95% of the population. However, duplicating Rwanda's success will be challenging due to the country's small size. Peters mentioned that countries like Nigeria, which are much larger, present more obstacles. He suggested that a food cold chain model with established commercial capacity will be necessary for success. Peters mentioned the successful transportation of fresh food from small farms in Africa to consumers in Europe as a model that could be applied to moving vaccines. However, the challenge of ultra-cold storage requirements for COVID-19 vaccines, which solar direct-drive fridges are not equipped to handle, must also be considered. Rwanda and the DRC have experience with vaccines requiring ultra-cold storage, such as a vaccine used during the Ebola outbreak. This vaccine was kept at minus 60-80C for up to 6.5 days using "super thermos" coolers filled with synthetic alcohol ice. However, the quantities needed for a COVID-19 vaccine would be much larger. Sagar pointed out that very few African economies have the capability for ultra-cold chain storage. Peters is optimistic that COVID-19 vaccines will only need standard cold storage between 2-8C, which can be provided by solar direct-drive refrigerators at rural health centers. He expressed concern that if vaccines require colder temperatures, it will pose a significant new challenge for mainstream cold chains.