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Jacob John of Christian Medical College in Vellore and his colleagues, showed strikingly similar results in 500 kids there in 2013. When news of the encouraging findings began circulating through the polio community last year, health officials were grappling with a polio outbreak in the Horn of Africa. It had erupted in May 2013 near Mogadishu, Somalia’s capital, and Kenya’s Dadaab refugee camp, and spread fast across the war-torn region. Over the next few months, GPEI tried every new tactic that seemed to have helped in other outbreaks: vaccinating older kids and sometimes adults, instead of just children under age 5; setting up vaccination posts along major transit routes; and, where access was compromised, sending in volunteers to deliver vaccine in short, quick bursts. Then in December GPEI and the Kenyan Ministry of Health decided to try the combination strategy, despite the challenges of administering shots and the fear that people would not accept them. Vaccinators in Dadaab targeted 126,000 kids with a onetwo punch of IPV and OPV drops, as CDC epidemiologist Concepcion Estivariz and colleagues described in the 21 March issue of the Morbidity and Mortality Weekly Report.
Polio strongholds Where the virus persists and confict limits access, the injected vaccine may help.
Wild poliovirus type 1, 2014 Endemic countries Importation countries Source: World Health Organization
lenge” dose of OPV, as a proxy for infection with the wild type virus. To gauge how well the two vaccines blocked transmission, the researchers looked at viral shedding in the children’s stool, a measure of so-called gut immunity, several days after the challenge. The team found the greatest reduction in viral shedding in the children who had received IPV— up to 75% in the oldest age group. In other words, IPV did a better job at boosting gut immunity than another dose of OPV did. The Moradabad study “showed very elegantly and persuasively that giving a dose of IPV to a child receiving the full dose of OPV does an excellent job at boosting intestinal immunity,” says Stephen Cochi of the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta. The Lancet study, led by 862
No one is asserting that one campaign turned the tide in Dadaab, and immunological data are lacking. What’s remarkable, experts say, is that, a few glitches aside, the program was able to pull it off, and coverage reached about 95%. Nigeria isn’t waiting for more data. The country just wrapped up its first IPV-OPV campaign in the northern states of Borno and Yobe. Plans are afoot to try it in Pakistan in the Federally Administered Tribal Areas. But as the December Dadaab pilot showed, the cost and logistics of IPV are still daunting, so these campaigns should be saved for the toughest spots—“small geographic areas where transmission is occurring and access to kids is tough,” Modlin says. As Estivariz puts it, that’s when you “go in and give them everything you’ve got.” ■
MATHEMATICS
Wheels when you need them Can special algorithms help keep shared bicycles rolling? By Chelsea Wald, in Vienna
G
rigorij Kuklin pulls his van over as far as he can while cars stream past. It’s nearly rush hour in Vienna, and intermittent July rainstorms are worsening the traffic. A driver for Citybike Wien, Vienna’s bike-sharing system, Kuklin is helping test a new algorithm to route vans like his, which pick up bikes from stations that are full and take them to ones that are empty. Kuklin is keen to see whether mathematics can really make his job more efficient. But the instructions that appear on his smart phone are telling him to stop and pick up bikes where it’s not safe. “I’m not going to do that,” he says as he jumps back into the van and pulls into traffic. Perhaps it was the right call. But computer scientist Günther Raidl of the Vienna University of Technology, who is developing the algorithm, is hopeful that his work will ultimately help drivers like Kuklin better address what bike-sharing operators call the “rebalancing” problem. Raidl is one of many scientists drawn to a challenge that is both mathematically complex and practically important. “There may be 20 to 30 researchers that are devoting significant parts of their research agendas to rebalancing,” says computer scientist David Shmoys of Cornell University. For most, it’s still a theoretical exercise, but a few have also seen their work applied. Shmoys collaborates with NYC Bike Share, the company that operates New York City’s system; his algorithms now provide “the overarching vision for how we like our system to look,” says Michael Pellegrino, director of operations for NYC Bike Share. Cornell is also running tests in Chicago, Illinois. Some 600 cities in 52 countries have introduced bike-sharing systems, according to the Earth Policy Institute in Washington, D.C.; Vienna, which was among the early adopters in 2003, now has 1500 bikes. (The largest system, in Wuhan, China, has 90,000.) Nearly all of them share the same problem: Riders tend to take some routes—downhill, for example—and not others. As a result, the bikes tend to collect in a few places. sciencemag.org SCIENCE
22 AUGUST 2014 • VOL 345 ISSUE 6199
Published by AAAS
Downloaded from www.sciencemag.org on August 23, 2014
The two trials were conducted in India, where the battle against polio has been perhaps the most intense—the Science study in Moradabad in the northern state of Uttar Pradesh in 2011, and the Lancet in Vellore in the southern state of Tamil Nadu in 2013. India reported its last case of polio in January 2011, but when the Moradabad study began, that victory was by no means secure. Indeed, Moradabad was the “polio heartland” at the time, says Hamid Jafari, who directs polio research and operations at WHO in Geneva, Switzerland, and who led the Science study. The virus thrived in the heat and the open sewers, and the huge burden of diarrhea interfered with the vaccine. In this holdout, where kids were bombarded with OPV from birth and still poliovirus circulated, OPV clearly needed some help. Jafari and his colleagues wondered if IPV might provide it. To find out, the collaborators recruited almost 1000 kids in three age groups— 6- to 11-month-olds, 5-year-olds, and 10-year-olds—who had all received multiple doses of OPV. At the start of the study, children were given either a dose of IPV or OPV, or, for controls, no vaccine. Four weeks later, each child was given a “chal-
PHOTO: TIM CLAYTON/CORBIS
A bicycle station in New York City has almost filled up.
For users, an unbalanced system is a drag: You either can’t get a bike, or there’s no room to drop one off. For operators, it’s a costly headache. Unbalanced systems can cause riders to abandon their bikes, which increases the risk of theft. In Vienna, two to three vans haul 20 bikes at a time from full stations to empty ones. In New York City’s 6000-bicycle system, introduced last year, managing rebalancing “is a good part of my day-to-day,” Pellegrino says. Oliver O’Brien of University College London, who runs the online Bike Share Map, says that in most systems, drivers or dispatchers “squint at a map” of the system to rebalance it. “They’ll say ‘OK, these ones are full, these ones are empty,’ ” and then route a truck between them, he says. That often doesn’t work well enough; unbalanced stations are among the top user complaints in many cities. Mathematicians believe there has to be a more efficient way. Raidl’s approach, which he developed with colleagues at the Austrian Institute of Technology, resembles the “pickup and delivery vehicle routing” algorithms that package delivery services use to route their trucks most efficiently. His algorithm—which gives updated suggestions throughout the day— also takes into account a forecast of demand based mainly on season, day of the week, and weather. The problem is too complex to allow an exact solution; instead, Raidl came up with ways to approximate one.
The algorithm works well on paper, but this summer’s trials showed that its suggestions don’t always suit drivers in the thick of things. It can also irk drivers by suggesting they pick up fewer than the 20 bikes the van can carry, which “seems inefficient,” even though it may not be, Kuklin says. New York also has a fleet of trucks to do the rebalancing. The system that Cornell developed works differently than Raidl’s: It doesn’t give drivers specific instructions, but produces an online map showing the stations that are farthest off from the predicted need. Dispatchers use the map, in combination with precomputed truck routes, to guide the drivers, especially overnight when there’s time to prepare for the next day. New York drivers, too, balk when instructed not to fill their trucks to capacity, says Ph.D. student Eoin O’Mahony, who works with Shmoys; luckily, he adds, “we’ve seen from data that moving nothing but truckloads of bikes gets you close” to the same solution anyway, so the map now prescribes only full loads. Because traffic seriously hinders the trucks during rush hour, New York has also introduced ricksha-like trailers, powered by human pedaling, which carry up to three bicycles at a time. (In rush hour, a single trailer can move more bikes per hour than a truck, O’Mahony says.) He and Shmoys came up with an algorithm for routing the trailers as well. The researchers first figured
SCIENCE sciencemag.org
out which stations normally ran empty and which full; then they paired nearby stations—one normally empty and one normally full. Bike trailers can now shuttle between those two stations. A London-based company called Stage Intelligence envisions an alternative to such top-down planning. Computer scientist Lin Li modeled autonomous rebalancing trucks, which self-organize like a bee colony, he says. The trucks flit from station to station like bees to flowers, attracted by signals that the stations feed into the model, announcing whether they are short of bikes or have too many. No operator is ready to give rebalancing over to an algorithm entirely, because it can never know everything. A big sporting event or a transit failure can drastically change demand or traffic conditions; media attention or political pressure could force an operator to give a certain station priority. That’s why in New York, human dispatchers are ultimately in charge, Pellegrino says. And sometimes, the riders themselves do part of the rebalancing. Some cities are giving users rewards—such as a small refund or extra riding time—if they ride against the flow, Shmoys says. “That’s another means for letting rebalancing be done in an automatic kind of way.” ■ Chelsea Wald is a science writer in Vienna. 22 AUGUST 2014 • VOL 345 ISSUE 6199
Published by AAAS
863
Jacob John of Christian Medical College in Vellore and his colleagues, showed strikingly similar results in 500 kids there in 2013. When news of the encouraging findings began circulating through the polio community last year, health officials were grappling with a polio outbreak in the Horn of Africa. It had erupted in May 2013 near Mogadishu, Somalia’s capital, and Kenya’s Dadaab refugee camp, and spread fast across the war-torn region. Over the next few months, GPEI tried every new tactic that seemed to have helped in other outbreaks: vaccinating older kids and sometimes adults, instead of just children under age 5; setting up vaccination posts along major transit routes; and, where access was compromised, sending in volunteers to deliver vaccine in short, quick bursts. Then in December GPEI and the Kenyan Ministry of Health decided to try the combination strategy, despite the challenges of administering shots and the fear that people would not accept them. Vaccinators in Dadaab targeted 126,000 kids with a onetwo punch of IPV and OPV drops, as CDC epidemiologist Concepcion Estivariz and colleagues described in the 21 March issue of the Morbidity and Mortality Weekly Report.
Polio strongholds Where the virus persists and confict limits access, the injected vaccine may help.
Wild poliovirus type 1, 2014 Endemic countries Importation countries Source: World Health Organization
lenge” dose of OPV, as a proxy for infection with the wild type virus. To gauge how well the two vaccines blocked transmission, the researchers looked at viral shedding in the children’s stool, a measure of so-called gut immunity, several days after the challenge. The team found the greatest reduction in viral shedding in the children who had received IPV— up to 75% in the oldest age group. In other words, IPV did a better job at boosting gut immunity than another dose of OPV did. The Moradabad study “showed very elegantly and persuasively that giving a dose of IPV to a child receiving the full dose of OPV does an excellent job at boosting intestinal immunity,” says Stephen Cochi of the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta. The Lancet study, led by 862
No one is asserting that one campaign turned the tide in Dadaab, and immunological data are lacking. What’s remarkable, experts say, is that, a few glitches aside, the program was able to pull it off, and coverage reached about 95%. Nigeria isn’t waiting for more data. The country just wrapped up its first IPV-OPV campaign in the northern states of Borno and Yobe. Plans are afoot to try it in Pakistan in the Federally Administered Tribal Areas. But as the December Dadaab pilot showed, the cost and logistics of IPV are still daunting, so these campaigns should be saved for the toughest spots—“small geographic areas where transmission is occurring and access to kids is tough,” Modlin says. As Estivariz puts it, that’s when you “go in and give them everything you’ve got.” ■
MATHEMATICS
Wheels when you need them Can special algorithms help keep shared bicycles rolling? By Chelsea Wald, in Vienna
G
rigorij Kuklin pulls his van over as far as he can while cars stream past. It’s nearly rush hour in Vienna, and intermittent July rainstorms are worsening the traffic. A driver for Citybike Wien, Vienna’s bike-sharing system, Kuklin is helping test a new algorithm to route vans like his, which pick up bikes from stations that are full and take them to ones that are empty. Kuklin is keen to see whether mathematics can really make his job more efficient. But the instructions that appear on his smart phone are telling him to stop and pick up bikes where it’s not safe. “I’m not going to do that,” he says as he jumps back into the van and pulls into traffic. Perhaps it was the right call. But computer scientist Günther Raidl of the Vienna University of Technology, who is developing the algorithm, is hopeful that his work will ultimately help drivers like Kuklin better address what bike-sharing operators call the “rebalancing” problem. Raidl is one of many scientists drawn to a challenge that is both mathematically complex and practically important. “There may be 20 to 30 researchers that are devoting significant parts of their research agendas to rebalancing,” says computer scientist David Shmoys of Cornell University. For most, it’s still a theoretical exercise, but a few have also seen their work applied. Shmoys collaborates with NYC Bike Share, the company that operates New York City’s system; his algorithms now provide “the overarching vision for how we like our system to look,” says Michael Pellegrino, director of operations for NYC Bike Share. Cornell is also running tests in Chicago, Illinois. Some 600 cities in 52 countries have introduced bike-sharing systems, according to the Earth Policy Institute in Washington, D.C.; Vienna, which was among the early adopters in 2003, now has 1500 bikes. (The largest system, in Wuhan, China, has 90,000.) Nearly all of them share the same problem: Riders tend to take some routes—downhill, for example—and not others. As a result, the bikes tend to collect in a few places. sciencemag.org SCIENCE
22 AUGUST 2014 • VOL 345 ISSUE 6199
Published by AAAS
Downloaded from www.sciencemag.org on August 23, 2014
The two trials were conducted in India, where the battle against polio has been perhaps the most intense—the Science study in Moradabad in the northern state of Uttar Pradesh in 2011, and the Lancet in Vellore in the southern state of Tamil Nadu in 2013. India reported its last case of polio in January 2011, but when the Moradabad study began, that victory was by no means secure. Indeed, Moradabad was the “polio heartland” at the time, says Hamid Jafari, who directs polio research and operations at WHO in Geneva, Switzerland, and who led the Science study. The virus thrived in the heat and the open sewers, and the huge burden of diarrhea interfered with the vaccine. In this holdout, where kids were bombarded with OPV from birth and still poliovirus circulated, OPV clearly needed some help. Jafari and his colleagues wondered if IPV might provide it. To find out, the collaborators recruited almost 1000 kids in three age groups— 6- to 11-month-olds, 5-year-olds, and 10-year-olds—who had all received multiple doses of OPV. At the start of the study, children were given either a dose of IPV or OPV, or, for controls, no vaccine. Four weeks later, each child was given a “chal-
PHOTO: TIM CLAYTON/CORBIS
A bicycle station in New York City has almost filled up.
For users, an unbalanced system is a drag: You either can’t get a bike, or there’s no room to drop one off. For operators, it’s a costly headache. Unbalanced systems can cause riders to abandon their bikes, which increases the risk of theft. In Vienna, two to three vans haul 20 bikes at a time from full stations to empty ones. In New York City’s 6000-bicycle system, introduced last year, managing rebalancing “is a good part of my day-to-day,” Pellegrino says. Oliver O’Brien of University College London, who runs the online Bike Share Map, says that in most systems, drivers or dispatchers “squint at a map” of the system to rebalance it. “They’ll say ‘OK, these ones are full, these ones are empty,’ ” and then route a truck between them, he says. That often doesn’t work well enough; unbalanced stations are among the top user complaints in many cities. Mathematicians believe there has to be a more efficient way. Raidl’s approach, which he developed with colleagues at the Austrian Institute of Technology, resembles the “pickup and delivery vehicle routing” algorithms that package delivery services use to route their trucks most efficiently. His algorithm—which gives updated suggestions throughout the day— also takes into account a forecast of demand based mainly on season, day of the week, and weather. The problem is too complex to allow an exact solution; instead, Raidl came up with ways to approximate one.
The algorithm works well on paper, but this summer’s trials showed that its suggestions don’t always suit drivers in the thick of things. It can also irk drivers by suggesting they pick up fewer than the 20 bikes the van can carry, which “seems inefficient,” even though it may not be, Kuklin says. New York also has a fleet of trucks to do the rebalancing. The system that Cornell developed works differently than Raidl’s: It doesn’t give drivers specific instructions, but produces an online map showing the stations that are farthest off from the predicted need. Dispatchers use the map, in combination with precomputed truck routes, to guide the drivers, especially overnight when there’s time to prepare for the next day. New York drivers, too, balk when instructed not to fill their trucks to capacity, says Ph.D. student Eoin O’Mahony, who works with Shmoys; luckily, he adds, “we’ve seen from data that moving nothing but truckloads of bikes gets you close” to the same solution anyway, so the map now prescribes only full loads. Because traffic seriously hinders the trucks during rush hour, New York has also introduced ricksha-like trailers, powered by human pedaling, which carry up to three bicycles at a time. (In rush hour, a single trailer can move more bikes per hour than a truck, O’Mahony says.) He and Shmoys came up with an algorithm for routing the trailers as well. The researchers first figured
SCIENCE sciencemag.org
out which stations normally ran empty and which full; then they paired nearby stations—one normally empty and one normally full. Bike trailers can now shuttle between those two stations. A London-based company called Stage Intelligence envisions an alternative to such top-down planning. Computer scientist Lin Li modeled autonomous rebalancing trucks, which self-organize like a bee colony, he says. The trucks flit from station to station like bees to flowers, attracted by signals that the stations feed into the model, announcing whether they are short of bikes or have too many. No operator is ready to give rebalancing over to an algorithm entirely, because it can never know everything. A big sporting event or a transit failure can drastically change demand or traffic conditions; media attention or political pressure could force an operator to give a certain station priority. That’s why in New York, human dispatchers are ultimately in charge, Pellegrino says. And sometimes, the riders themselves do part of the rebalancing. Some cities are giving users rewards—such as a small refund or extra riding time—if they ride against the flow, Shmoys says. “That’s another means for letting rebalancing be done in an automatic kind of way.” ■ Chelsea Wald is a science writer in Vienna. 22 AUGUST 2014 • VOL 345 ISSUE 6199
Published by AAAS
863
