Nairobi — Kenya seemed to be on track to win the fight against malaria. It distributed millions of insecticide-treated bed nets. It fumigated countless homes. It made drugs and diagnostic testing cheap and available.
For several years, it was also rewarded with a fall in malaria cases. But now progress has stalled. Last year, there were 10.7 million malaria cases, up from 7.9 million in 2017.
According to the Kenya National Bureau of Statistics, malaria is still the second biggest cause of reported deaths after respiratory infections, with nearly 70 percent of the country's 46 million people at risk from the disease.
So what has gone wrong?
For one, growing resistance among mosquitoes to the commonly used pyrethroid-based insecticides, especially in high-prevalence areas around Lake Victoria in western Kenya.
Frontline approaches such as bed nets and indoor spraying - key to Kenya's scaled-up response - are "reaching their limits" because of resistance, according to Fredos Okumu, director of science at the Ifakara Health Institute, a Tanzania-based research outfit.
Yet Kenya plans to distribute 15 million treated bed nets this year. According to a multi-country World Health Organisation study, insecticide-treated nets can still be highly effective - but only in areas with "moderate levels" of resistance to pyrethroids.
Another problem for Kenya is that its historical success against the Anopheles mosquito, which transmits the malaria parasite between humans, has been uneven.
For example, Baringo County on the western edge of the Rift Valley has one of the country's highest prevalence rates. Like other remote semi-arid regions, it suffers from a weak health system that struggles to attract staff, hampering the detection and treatment of malaria cases.
The county government has also been slow to respond to the local conditions that exacerbate malaria - water pans and man-made water tanks synonymous with a pastoralist-based economy that also serve as mosquito larvae breeding grounds.
Follow the money
Sustained and predictable funding is key to tackling malaria. But falling investment - both by the Kenyan government and international bodies - has impacted the fight against malaria, and not just in East Africa.
"We need increased investment in applying the currently mandated interventions evenly and to a high standard," said Philip Bejon, of KEMRI Wellcome Trust, a Nairobi-based health research institution.
The WHO's 2018 World Malaria Report again warned (it first raised the alarm in 2017) that funding levels are too low, and said "we are off course" to meet two critical 2020 milestones - reducing case incidence and death rates by at least 40 percent from 2015 levels.
In Kenya, the Global Fund to Fight AIDS, Tuberculosis and Malaria - the biggest funder of local malaria programmes - has cut its 2018-20 spending by more than half, to $63 million.
The Roll Back Malaria initiative, the largest global platform for coordinated action, estimates that Kenya actually needs more than $427 million over the same period.
Yet the Kenyan government itself, responding to the fall in prevalence, cut its spending on malaria by 20 percent between 2014 and 2017.
Any let-up in the anti-malaria response could see the disease rebound as a more dangerous drug-resistant version, warned Desmond Chavasse, senior vice president at Population Services International, an NGO that specialises in health solutions around the world.
"Once you are on this road, there is no going back," Chavasse told The New Humanitarian. "Once you ease a bit, you get a backlash that is worse than where you started."
A change in strategy?
According to the WHO's 2018 report, when antimalarial action stumbles, new tools and strategies are needed - especially as the problem of resistance looms larger.
Among those new approaches is what is called Mass Drug Administration, or MDA. This involves giving a full dose of antimalarial drugs to everybody in a given area, irrespective of whether they have symptoms of malaria.
The goal is to wipe out not the malaria-carrying mosquitos but the parasites in the human bloodstream they transmit.
A 2015 report by the WHO said MDA can rapidly reduce the prevalence and incidence of malaria in the short term. But it recommended that MDA be used in areas where there is good access to treatment, effective implementation of vector control and surveillance, and where the risk of re-introduction is minimal.
MDA has been used in Kenya's Ngodhe Island in Lake Victoria, a highly endemic area. It cut prevalence to just 0.21 percent in 120 days (national prevalence is eight percent) using bed nets plus the antimalarial drugs artemisinin-piperaquine and primaquine.
Even though this trial was on an island, reducing the chances of transmission, the study concluded that the importation of malaria by travellers still posed a challenge in keeping Ngodhe malaria-free.
A Chinese company is now laying the groundwork for a far more ambitious MDA pilot programme among 10,000 people in Kenya's coastal city of Mombasa.
The company, New South, has already trialled its approach in the Comoros. It says it eliminated malaria from two of the three islands of the Indian Ocean archipelago using artemisinin-based combination therapy (ACT) - the most commonly recommended treatment.
But Mombasa is a different proposition: an endemic area with a busy, highly mobile population - the risk is that people would be arriving in the city unvaccinated and could reintroduce the malaria parasite.
Repeated doses of ACT could also trigger the other worry regarding MDA, the potential for the build-up of resistance.
Nevertheless, Bernhards Ogutu, a researcher at the Kenya Medical Research Institute, supports New South's strategy. "The Chinese should be bold enough and go to endemic countries and get MDA going so as to prove it works," he told TNH.
A vaccine trial
Less controversially, Kenya is one of three countries where a new vaccine is about to be tested. Mosquirix, the brand name for "RTS,S" will be administered as part of routine child immunisation programmes in nine endemic counties in western Kenya, although its planned launch this week was delayed.
RTS,S provides a partial defence against the first stages of the disease shortly after the malaria parasite enters the bloodstream. Doses will be administered to children at six, seven, nine, and 24 months of age, and the four-stage course is expected to provide a protection rate of 40 percent.
Manufactured by GlaxoSmithKline, it acts only against the most common and dangerous pathogen, "Plasmodium falciparum". The WHO regards it "as a complementary malaria control tool that could be added to (and not replace) the core package" of recommended preventive, diagnostic, and treatment measures.
New classes of insecticides for use in bed nets and sprays are on their way, as well as bait devices that attract and kill mosquitoes.
But for Okumu there is no silver bullet. A successful response needs to be full-spectrum, from drugs to bed nets, as well as old-fashioned environmental management and public education, he said.
Chavasse agreed, and added: "If there isn't any new money, then we need to use the money we have more carefully."
(This article was developed with the support of Journalismfund.eu's Money Trail Project.)