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In 2016, the last major outbreak of yellow fever (in Congo and Angola) depleted not once, but twice, world stocks of vaccines against this viral disease, endemic in 44 countries from Africa and Latin America and for which there is no treatment. The outbreak spread to the capitals of Angola and the Democratic Republic of the Congo and 11 cases were detected in China, raising fears of the worst in a country with 1.400 millions of inhabitants and without immunity. Now a study International has confirmed that giving a fifth of a normal dose of the vaccine provides protection, opening the door to protecting five times as many people from the stocks current.
“When the great outbreak occurred in Africa in 2016, the world was not prepared to respond,” says Aitana Juan, the lead author of the report led by Epicentre, the epidemiological research center of Doctors Without Borders (MSF). Producing the yellow fever vaccine takes about 12 months and it is difficult to forecast the volumes that will be needed each year to respond to outbreaks. Hence the vaccine shortage. On that occasion, the World Health Organization (WHO) recommended using diluted doses of the vaccine as an exceptional measure, but called on the scientific community to investigate the issue further in the face of future emergencies. The result is the first study to evaluate the four vaccines for this disease approved by the WHO in sub-Saharan African populations at the same time.
To date, only it had been investigated the fractionation of one of the four vaccines in young Brazilian military personnel. “What happens is that these results cannot be generalized: the defenses of a boy in good shape are not the same as those of a person over 50 years of age or with HIV; even less, considering that infection by viruses such as Zika offers a certain immunity, ”explains co-author Derick Kimathi, affiliated with the Kenya Medical Research Institute-Wellcome Trust. The current study, in which the Pasteur Institute in Dakar and the WHO also collaborated, focused on adults aged 18 to 59 years. Other ongoing research is evaluating the efficacy and safety of divided doses in children and people with HIV, and its results are expected within a year.
Next stop: Asia?
Yellow fever is a hemorrhagic fever acute transmitted by a mosquito and causing 30,000 deaths per year; nine out of ten deaths occur in sub-Saharan Africa. 80% of cases are asymptomatic, but half of those who suffer from them die within a few days from internal bleeding and severe damage to the liver and lungs. “When we detect an epidemic outbreak, it means that the infection is already widespread. For this reason, it is essential to prevent through routine childhood vaccination and control of mosquito populations, ”explains Aitana Juan.
80% of cases are asymptomatic, but half of those who suffer from them die within a few days from internal bleeding and severe damage to the liver and lungs
The yellow fever vaccine, created in 1937, is so effective and safe that a single normal dose protects for life. A total of 40 of the 44 countries where it is endemic have incorporated it into their vaccination calendar and, in addition, international travelers must prove by means of a health card that they are immunized to go to risk areas. Despite everything, the outbreaks have been increasing for 30 years and are spreading in Central and South America. For example, there have been recurrent outbreaks in areas of Brazil where cases have never been reported, but the vector mosquito does exist (Aedes aegypti), It can also transmit viruses such as dengue, Zika, and chikungunya.
According to Kimathi, the increase in cases is due to a combination of factors: the success of vaccination and vector control campaigns, which, paradoxically, has led some countries to lower their guard; changes in the ecology of mosquitoes due to global warming and even the picaresque. “There are people who buy a false international certificate of vaccination to travel without being immunized; at some border posts you can buy them for only 10 euros, ”says the researcher in reference to the systemic problem of corruption.
There are people who buy a fake international certificate of vaccination to travel without being immunized; in some border posts you can buy them for only 10 euros, ”says the researcher referring to the systemic problem of corruption.
The disease can be prevented, but not eradicated. Monkeys are the main reservoirs for this arbovirus, which is transmitted from animal to animal through mosquitoes and, occasionally, to humans. In urban settings, mosquitoes can pass the virus between people. And as with other zoonotic diseases such as Ebola, the more destruction of natural ecosystems, the greater the risk of infection – with the added problem that viruses now travel by plane, as COVID-19 continues to demonstrate.
Yellow fever passed from Africa to America with the slave trade and stayed. China has mosquitoes Aedes aegypty, so the risk is real. “If the virus were successfully introduced into Asia, especially in large densely populated cities, it could be catastrophic,” says Juan. “Administering divided doses of vaccines will allow us to better respond to large outbreaks. But let’s not forget: the most important thing is still prevention ”.
Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.