https://www.nature.com/articles/d41586-020-01011-6
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The world’s most contagious virus has killed thousands in the Democratic Republic of the Congo, and 23 countries have suspended measles vaccination campaigns as they cope with SARS-CoV-2.
A driver prepares to transport vaccines into rural areas in the Democratic Republic of the Congo.
Credit: Junior Kannah/AFP Via Getty
Cases began to spike here in October 2018. Children became weak, feverish and congested, with red eyes and painful sores in their mouths, all with the telltale rash of measles. “We have been running after the virus ever since,” says Balcha Masresha, an epidemiologist with the World Health Organization (WHO) regional Africa office in Brazzaville in the neighbouring Republic of Congo. The situation has mushroomed into what WHO experts say might be the largest documented measles outbreak in one country since the world gained a measles vaccine in 1963 (see ‘Measles cases on the rise’).
The other deadly virus
In poor countries, measles is a killer, especially in combination with malnutrition and vitamin A deficiency. Estimates are uncertain, but the death rate in developing countries hovers around 3–6%, and it can spike as high as 30% in the worst outbreaks, according to the WHO. Its victims often die of complications including pneumonia or diarrhoea and dehydration. Those who recover can be left with permanent disabilities, including blindness, hearing loss and brain damage. The virus also impairs the immune system for months or years after infection, creating “immune amnesia” that leaves children vulnerable to other infections.
The virus is so contagious that few unvaccinated people who come into contact with it are spared its effects. Scientists define infectiousness using the ‘reproduction number’ — how many people, on average, would be infected by a single person with the virus, in a population that has no immunity. For Ebola, that number is estimated at 1.5–2.5. The new coronavirus terrifying the world seems to be somewhere between 2 and 3. Measles tops the charts with a reproduction number of 12–18, which makes it the most contagious virus known. You don’t need to be in the same room as an infected person to catch the virus — it is spread by respiratory droplets that can linger in the air for hours.
Two doses of a safe and effective vaccine can prevent measles; one dose provides partial protection. Many children in poor countries are lucky to get a single dose. Because the virus is so contagious, 92–95% of a population needs to be fully immunized to ward off outbreaks. In the DRC, only 57% of children received even one dose of measles vaccine in 2018, according to a UNICEF study, creating ideal conditions for the virus to explode.
In other countries, too, measles is a constant, simmering at low levels until the number of children susceptible to the virus builds up and it takes off (see 'Large measles outbreaks'). “Pretty much name any country and you will find measles there,” says Robb Linkins, a measles specialist in the global immunization division at the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, and chair of the Measles & Rubella Initiative, a partnership of five organizations.
In Madagascar, a shortage of measles vaccine helped fuel an outbreak that has swept the island nation starting in 2018, causing more than 240,000 cases and 1,000 deaths.
And in Ukraine, after a child died of unrelated causes following a measles jab in 2008, vaccination coverage plummeted from 95% that year to 31% in 2016, says Linkins. He says no one was surprised when, in 2017, a huge outbreak hit that has led to more than 115,000 cases.
Failure modes
The DRC has difficulties on a number of levels. The country has such a high birth rate — 3.5 million children are born each year — that it needs to conduct mass vaccination campaigns every two years. Those campaigns, in which tens of thousands of health workers fan out across this vast country, are a logistical nightmare. First, the government has to get the vaccine from the capital, Kinshasa, to remote villages that can be reached only by helicopter — or through bloody conflict zones in the eastern part of the country.
The vaccine must be kept between 2 °C and 8 °C from the time it leaves the warehouse until it is administered — a challenge in a tropical environment where power outages are frequent. Health workers must be trained to inject it safely, a much more difficult task than dropping liquid polio vaccine on a child’s tongue. The vaccine comes as a powder, which must be reconstituted with an accompanying solution of sterile diluent and then used within 6 hours. It also comes in ten-dose vials; worried about wastage, vaccinators are sometimes hesitant to open one when just a few children show up to a session, so the children go unimmunized.
On top of that, clinics have to be open when parents can make it, and vaccinators have to be paid or they won’t come, either — a problem in a country plagued with corruption.
Health workers are stretched thin at the best of times, and the DRC has been battling Ebola, outbreaks of cholera and yellow fever — and now the coronavirus. And measles is such a constant that it often takes lower priority than other diseases. In addition to these outbreaks, “DRC is confronted not only with political challenges but a long-running civil war,” says Katrina Kretsinger, a medical epidemiologist and global measles expert at the WHO in Geneva, Switzerland. “When in a firefighting mode, it is hard to sit back and say, ‘Here is the long-term view of what needs to happen’” with measles, she says.
This long article continues at: https://www.nature.com/articles/d41586-020-01011-6
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