The Democratic Republic of the Congo (DRC) has declared an official end to its 11th Ebola outbreak nearly six months after it began, marking the first time in years the vast central African country has been free of the deadly haemorrhagic fever.

Eteni Longondo, the DRC’s minister of health, and the World Health Organization (WHO) made the announcement on 18 November after no new cases of the viral disease had been recorded in the country’s western Équateur province for 42 days, or the time of two maximum incubation periods for Ebola. In this outbreak, there were 55 deaths and 75 people who had recovered out of 119 confirmed and 11 probable cases.

The outbreak, which was announced on 1 June, surfaced shortly before the DRC called an end to a separate Ebola epidemic – hundreds of miles away in the east of the country – that killed 2280 people over nearly two years. Genetic sequencing showed that the two virus strains were unrelated.

The latest outbreak stretched vast distances across dense rainforests and remote waterways as well as busy urban areas. It was halted thanks to “cold chain” vaccine storage technology and community-based health workers who vaccinated 40,000 people deemed at high risk of contracting the disease, according to experts.

“The geography was very difficult in terms of accessibility,” says Ngoy Nsenga at the WHO. “It required serious logistics, and so this ultracold-chain technology was very important.”

Known as the Arktek and originally developed by the Global Good Fund, a US-based social enterprise, the cylinder-shaped “super thermos” devices can store 500 vaccine doses at -80°C for up to a week with no external power source. This meets the cold temperature requirements of the Merck Ebola vaccine, as well as those of Pfizer and BioNTech’s new covid-19 vaccine, which bodes well for vaccination in lower-income countries with less-developed infrastructure.

“But there were so many factors in the management of the outbreak,” says Nsenga. “The DRC is gaining experience in stopping epidemics and the WHO has learned to react as quickly as we can.”

Bob Ghosn at the International Federation of Red Cross and Red Crescent Societies (IFRC) says working with local people was crucial to the success.

“Community engagement is key to stopping any outbreak,” says Ghosn, who helped deploy a team of 1000 IFRC community workers in Équateur. “We’ve got much better at it. Top-down messaging doesn’t work on its own – covid-19 has proved that.”

However, experts warn that the risk remains of another Ebola outbreak in the DRC – adding to the 11 since 1976. The disease, which can cause uncontrollable internal bleeding, is zoonotic and is believed to derive from a species of bat.

Natalie Roberts at Doctors Without Borders in France says future efforts are likely to improve with the use of monoclonal antibodies – laboratory-made molecules that can enhance the immune system.

“Due to the remote nature of this outbreak and other constraints, we weren’t able to use them as much as we wanted,” she says. “But they are very effective in the early stages of the disease.”

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FOR those of us who turn to science for answers, the Wuhan coronavirus outbreak is unsettling. We don’t know what proportion of infected people are likely to die (see “The three things we really need to know about the Wuhan coronavirus”); our figures for how many other people on average each carrier infects are only estimates; and the total number of cases is likely to be far higher than those confirmed so far. These three parameters are crucial for epidemiologists who use models to calculate how bad an outbreak will get, but we don’t yet know what values to punch into the models.

As cases in China soar, the list of unknowns gets even longer. It remains unclear whether the virus can spread before symptoms show. We don’t yet know how or when the virus is likely to have crossed over from bats (see “Coronavirus: Why infections from animals are such a deadly problem”), or why the first known human case of the virus seems to have no connection to the Wuhan food market where the outbreak appears to have begun. Is every case equally infectious, or are some people unlikely to pass it on, while others act as super-spreaders? And is the virus only deadly for those who are older or who already have chronic conditions?

“If the virus goes global, it could one day resemble flu, which every year causes hundreds of thousands of deaths”

What we do know is that the outbreak is likely to go one of three ways. As this magazine went to press, the outbreak seemed on the verge of becoming a pandemic – in which multiple epidemics of an infection take place across the world. From here, the virus may either peter out or go truly global. We can’t know yet how many lives this would claim.

If it goes global, it could one day resemble flu, which every year causes an estimated 3 to 5 million cases of severe illness, and about 290,000 to 650,000 deaths. Flu can cause mild symptoms in some people and much worse ones in others, and most deaths occur in people over the age of 65 – all of which may be true for the new coronavirus.

There is another option. The race is now on to find drugs and vaccines that could help bring the virus under control and prevent global exposure. While drug development will take time, trials of existing drugs are already under way in China (see “New coronavirus: How soon will a treatment be ready and will it work?”). If successful, we may be able to save many lives – although we can’t yet calculate the number.

The number of Ebola cases in the Democratic Republic of Congo is rising faster, reaching a high of 27 confirmed cases in one day, according to the country’s health ministry. That surpasses the last record, set a few weeks ago, of 20 cases in one day.

The latest figures from the World Health Organisation (WHO) bring the total confirmed cases to 1400, including 891 deaths, most of which are among women and children. The uptick in cases may not be caused by the disease spreading more quickly, but could be a sign of doctors in the region being able to more accurately count cases in towns that were previously off-limits due to sectarian violence.

“The increase in the number of new cases in the Democratic Republic of Congo remains deeply concerning,” . “With often difficult to access settings, disruptions by incidents of sporadic violence by armed militias, and limited healthcare resources, this outbreak is taking place in one of the most challenging circumstances ever confronted by WHO.”

The outbreak began in August 2018 and healthcare workers have faced difficulty containing it due to lack of health infrastructure, mistrust in health workers among affected communities, and violent attacks in the region.

A total of 33 healthcare workers have also died, including WHO epidemiologist Richard Mouzoko, who was killed when armed militia members attacked a clinic in Butembo on 19 April. Conflict has been constant in the region for decades, with some 70 militia groups vying for control over mining in the area.

As the outbreak has continued, health workers and clinics have been specifically targeted with violence. Two clinics were firebombed in late February, and Doctors Without Borders temporarily pulled their workers out of the area to keep them safe.

After Mouzoko’s death, some of WHO’s Ebola response activities were shut down, but vaccination and case investigations have started again, , Tedros Adhanom Ghebreyesus.

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Drug swap

Ebola has broken out again. This time it is in the jungles of central Africa, where populations are small and scattered, and people know about the Ebola virus. That means the risk of a massive outbreak like the one in West Africa in 2014 is low.

Moreover, the World Health Organization (WHO) has been quick to activate the emergency response teams it developed after being criticised for its slow response to the earlier epidemic. Still, health officials say they “stand ready” to deploy their emergency stock of Ebola vaccine if things get out of hand – for example, if Ebola strikes an African metropolis as it did in 2014.

On 22 April, a man died on arrival at a hospital in Likati in the remote northern Bas-Uele province of the Democratic Republic of the Congo (DRC). His death was soon followed by that of his driver and a healthcare worker. Alarm bells rang, and the DRC announced on 11 May that there were nine suspected cases of Ebola. The next day the WHO made the outbreak official when one tested positive for the virus.

There was another positive test on 14 May, as the number of suspected cases grew to 19. The WHO and Congolese officials are now tracing 125 people who were in contact with any cases and must be quarantined.

They also want to know how the first man to die encountered the virus. The prime suspect is a wild animal, caught for meat. Ebola kills chimpanzees, which are eaten in the region, and whose populations could also suffer from this outbreak.

DĂ©jĂ  vu?

The 2014 epidemic spun out of control, killing more than 11,000 before it . The high death toll was partly because Ebola had never broken out in the region before. Congo, in contrast, has had a long history with the virus.

Ebola was discovered there in 1976. Congo’s seven known outbreaks since then have never exceeded 318 cases, and outbreaks since 2009 numbered only tens of cases, as people learned measures such as quarantining exposed people and not touching the dead.

Moreover, the current outbreak is far from any major cities: it takes three days to get to Likati from the Congolese capital Kinshasa. The 2014 epidemic also exploded because it spread fast in big cities such as Monrovia, Liberia.

Controlling the spread

However, the big fear is that this outbreak could indeed invade sprawling Kinshasa or nearby

Brazzaville in Republic of the Congo. Last week , a Swiss-based group that helps developing countries get vaccines, said it “stands ready to support the DRC government in its fight against Ebola if it needs vaccines”.

We first need to understand the outbreak, says Seth Berkley, head of Gavi. “If the people affected don’t move around a lot, it will probably be contained there [with classic quarantine]. If these people move around a lot, we will have to watch surrounding areas carefully.”

Gavi and US pharmaceuticals firm Merck have created an emergency stockpile of 300,000 doses of the firm’s Ebola vaccine. This proved highly effective when tested in 2015. It is even designed to tackle the Zaire strain of Ebola that is causing the current outbreak.

If Ebola reaches a big city, says Berkley, the affected government can officially request vaccines from that stockpile, which will be released if the WHO agrees. If used on people living in a radius around each case as soon as it emerges, it could stop the Ebola epidemic – the first chance ever to do that with a vaccine. But even 300,000 doses may not go far in a megacity of 11 million if vaccinators don’t work fast.

The South American Zika outbreak may have prompted a drop in the number of live births in Rio de Janeiro in late 2016. But some researchers believe Brazilian women avoiding getting pregnant isn’t the only reason for this trend.

Between October 2015 and January 2016,ĚýĚýwere born in Brazil that had microcephaly – abnormally small heads, a condition linked to infection with the Zika virus during pregnancy. By June, the World Health Organization began recommending that people in affected areas delay getting pregnant to avoid the risk of having babies with serious birth defects.

Last month, at Harvard UniversityĚýĚýthat this warning had not had a widespread impact on birth rates in Brazil last year. She suggested this was because a high proportion of pregnancies in the country – 40 per cent – are unplanned.

But new figures suggestĚýthe birth rate may have declined in the city of Rio de Janeiro during the second half of 2016. Castro cautions that the records aren’t yet complete, nor are they official figures.

However, Margaret Armstrong at theĚýGetulio Vargas Foundation in Rio and her team believe the figures indicate that the birth rate was below average during the period in question. They were given the data by Rio de Janeiro’sĚýMunicipal Health Secretariat, which had noticed a lower number of births.

Thousands fewer births

The figures hint that there may have been several thousand fewer babies than usual, says Armstrong. “It was more pronounced than I was expecting.” She and her team think the decline in live births could be as high as 15 per cent.

Despite the figures being incomplete, the researchers believe they are largely representative of the pattern at that time. Some of the decline may be explained by data from the end of the year not yet having been processed, but, even so, the drop in birth rate seems to have begun during the middle of the year.

The difference between national birth rates and local rates in Rio could be due to the Zika outbreak being particularly pronounced in the city, says at the University of California, Los Angeles.

Family planning decisions may be one factor in the decline in birth rate, but miscarriages could also be to blame. Nielsen and her colleagues have shown that, in a small sample of 125 infected pregnant women, Zika infection in the first trimester was linked to aĚý10 to 15 per cent increase in theĚý.

Undetectable miscarriage?

Armstrong’s team thinks Zika may also cause very early miscarriages, occurring before a woman even knows she is pregnant.Ěý“We thought there was a real possibility that Zika was attacking babies much earlier than was currently thought. The only way you would be able to show this was by looking at the birth records nine months after Zika had arrived in Rio de Janeiro,” says Armstrong.

Nielsen says this hypothesis is plausible. Zika can cross the placenta, and any virus that can do this has the potential to damage a fetus and cause miscarriage, she says. This is seen in both syphilis and chikungunya – another viral disease that struck Brazil last year.

When Armstrong’s team analysed the data, they found no link between chikungunya infections and birth rates. However, they did find a correlation between the drop in birth rates and the number of Zika cases recorded about 40 weeks earlier – the length of a pregnancy.

Falls in birth rate may affect Brazil’s economy, especially because the country is already experiencing a pension crisis, with the government struggling to accrue enough funds to pay an ageing population. “An imbalance in the number of workers who are paying in compared [with] the increasing number of people who survive longer – it doesn’t bear thinking of,” says Armstrong.

However, if the drop really is confined to Rio de Janeiro during only one part of 2016, the impact might be contained. “I think Brazil can recover,” says Nielsen. “This was very focal.”

Read more: Warmer weather could bring fresh Zika misery

We’re on the brink of wiping out polio, but the virus used in vaccines keeps evolving to become harmful again. The discovery of how the virus mutates to do this could lead to a safer vaccine.

Polio once killed hundreds of thousands of children every year. The disease has largely been brought under control by the oral polio vaccine, which contains a weakened form of the live poliovirus. We do have a vaccine that uses dead virus instead, but this is less effective at spreading immunity. When the weakened live vaccine reaches the intestine, the virus replicates and can be passed on to others in close contact, transmitting immunity to people who haven’t been vaccinated.

It’s an effective way of wiping out polio, but it carries a risk. From time to time, the weakened virus re-evolves the ability to cause disease, and spreads rapidly through unvaccinated populations. In the 10 years leading up to 2015, there were around 750 reported cases of paralysis caused by worldwide.

A new vaccine in development may put a stop to this. and colleagues at the University of California, San Francisco, have analysed the genes of 424 samples of VDPV from 30 different outbreaks, and compared them with the genetic makeup of the vaccine. They found that in every case, the weakened vaccine virus had undergone the same three evolutionary steps to become virulent again.

Evolving virus

The first step was to acquire mutations that enabled the virus to make proteins more easily, opening up the possibility for further evolution. Next, the poliovirus swapped genes with other viruses in the human gut that are better adapted to replicating there. “The virus doesn’t bother to create its own solutions, it steals them from other viruses,” says Andino.

Finally, the virus undergoes a few more mutations before becoming virulent. These mutations don’t alter the amino acids in the protein they encode. How exactly these “silent” mutations increase the virus’s fitness is unclear, but they seem to be more important than we realised, says Andino.

The whole process involves only around seven or eight mutations. Once they had identified these key steps, the researchers recreated the same mutations in the lab, and found that they made the vaccine virus replicate much more efficiently, and it was more deadly when tested on mice.

Using this knowledge, Andino’s team have designed a live virus vaccine that should have a lower risk of re-evolving virulence. By increasing the accuracy of how the virus replicates, they have reduced the likelihood of it acquiring the necessary mutations to become harmful again, and have also made it less able to swap genes with other viruses. “What we’re trying to do is put the virus in an evolutionary cage so it can’t evolve further,” says Andino.

Close to eradication

The team is hoping to begin a small clinical trial of this new vaccine in May. “This is exciting science,” says Roland Sutter, who works on polio eradication at the World Health Organization.

However, with worldwide eradication already in sight, a safer live vaccine may not actually be necessary. Once polio has stopped spreading, the WHO plans to switch completely to the dead virus vaccine to protect children.

Andino hopes the live vaccine already in use will be enough for the WHO to reach this stage, but he thinks we should be prepared in case the disease makes a comeback. Many times in the last 20 years, we have come close to wiping out polio, but the last step has proved to be a challenge, in part because political issues in its remaining footholds in Afghanistan, Pakistan and Nigeria have made it difficult for vaccination campaigns to operate.

The approach his team have used to understand the virus’s evolutionary pathway could also be applied to develop safer vaccines for other diseases, says Andino. “Live attenuated vaccines are the best, but nobody’s been thinking about them from an evolutionary perspective.”

Read more: Vaccines to be juggled in final assault against polio