This blog is the sixth in a seven-part series examining the nature and reasons for the near elimination of malaria in Zanzibar since 2000. This question forms the basis of a major new research project and big conversation about malaria led by the Zanzibar Research Centre for Socio-Economic and Policy Analysis (ZRCP). A link to the full report from ZRCP can be found here. This blog follows from Part Five A Small Island is Offering Big Lessons: Learning from the Malaria Elimination Efforts in Zanzibar, 2000-2020

Malaria in Zanzibar: a recap

Malaria is spread to humans through mosquito bites, with symptoms ranging from mild (fever, chills and a headache), to more severe (coma, severe anaemia, seizures, and difficulty breathing), and in too many cases death. Infants, children under 5 years, and pregnant women are at higher risk of severe infection. 

In the early 2000s, the World Health Organization (WHO) estimated there were between 300 and 500 million global cases of malaria a year, resulting in between 700,000 and 2.7 million deaths annually. During that time, 90% of the malaria disease burden was located in Africa.

New evidence on the economic and human cost of malaria in the 1990s helped inspire a renewed global elimination effort. A big push backed by global leaders, funders, and researchers and in Africa governments, health care professionals, volunteers, statisticians, and households was launched in the early 2000s, leading to a dramatic global reduction in the incidence of malaria, and after 2012, the successful trial and later in 2022 the scaling up of a malaria vaccine. After 2015 the WHO verified the complete elimination of malaria in a succession of countries.

Across Africa after 2000, the most successful countries were those that reduced the incidence of and mortality from malaria by 50%. Zanzibar went much further, to near elimination.

The Mosquito: Like a Horror Villain that Never Dies, Just Keeps Coming Back for the Sequels

The 1978 film directed by John Carpenter – Halloween – sees iconic horror-villain Michael Myers escaping from a mental hospital and returning to his hometown 15 years after murdering his sister. Michael spends much of the film lumbering knife in hand behind terrified Jamie Lee Curtis (the second sister). Towards the end of the film Laurie stabs Michael in the neck with a knitting needle, then turns her back assuming him dead…Michael duly opens his eyes, rises and resumes his bloody rampage. Michael kept being killed off and returning to life, as of writing (September 2025), for 12 sequels.

Zanzibar needs to learn from the film Halloween, not to assume the villainous mosquito has been vanquished, but instead to think carefully about the risks of a malaria resurgence.

There is precedence from history! Zanzibar reduced malaria to very low levels by 1969, but these gains were not sustained and malaria experienced a resurgence in the 1980s and 1990s. History could repeat itself. The risks of a malaria resurgence are real which may occur through migration of infected people or insecticide or artemisinin resistance among others. The Zanzibari mosquito is like Michael Myers and is ever-ready to return for a sequel.

An older example which provides a dramatic warning is that of Sri Lanka. Sri Lanka launched a malaria elimination programme in 1958 mainly structured around Dichlorodiphenyltrichloroethane (better known as DDT) spraying. The incidence of malaria declined rapidly in the early 1960s. After spraying was abandoned in the mid-1960s, the number of malaria cases increased from 18 in 1963 to over half a million cases in 1969, and continued to rise into the 1980s. Since being declared malaria free (no indigenous cases) in 2012 the sustainability of that elimination has been questioned, no doubt with the lesson of the 1960s in mind. In Sri Lanka a booming tourist industry and the influx of labour (partly due to foreign investment in manufacturing and tourism) and refugees from neighbouring malarious countries renders Sri Lanka vulnerable to a resurgence. There is also a concern that malaria-awareness is declining among medical professionals who are delaying diagnoses and diverting resources to other medical priorities. Recall Halloween when the heroine turned her back on the murderous villain……Sri Lanka has very good diagnostic coverage (microscopes and rapid diagnostic tests) but they are being used less frequently, even for individuals with fever and a recent history of travel to a malaria endemic country.

There are also contemporary warnings. Since 2020, the global number of estimated malaria cases has steadily increased, and almost 90% of this increase has occurred in countries in the WHO African Region. Twenty-four countries experienced an increase in case incidence, with 15 countries experiencing an increase of 63% or more in 2023 compared with 2015. Among the worst country’s in contributing to the increase in cases between 2022 and 2023 was Madagascar (+2.7 million cases), an island not far from Zanzibar. In 14 countries malaria case incidence in 2023 was similar to that of 2015 meaning almost a decade of progress had been lost. One study found a “steady increase in the annual parasite incidence (API) was observed in Zanzibar, from 2.7 (2017) to 3.6 (2021) cases per 1,000 population with marked heterogeneity between areas”.

A New Supercharged Mosquito Villain?

In Halloween the same villain (Michael Myers) kept returning. In other film series (Batman, Spiderman for example) the villain gets bigger, stronger, and more thrilling with each sequel. So it could be with malaria in Zanzibar.

The human biting Anopheles mosquito, of which there are around 130 species in Africa are predominantly found in water-rich rural areas. By contrast, the larvae of the Anopheles stephensi thrive in habitats like abandoned tires or cisterns that are commonly found in urban areas. An. stephensi is native to Asia and the Middle East and has been spreading slowly across Asia for the last three decades reaching Goa in the 1970s, southern India in the 1980s, and Sri Lanka in 2017, it was also detected in Djibouti (2012) and in Ethiopia (2016). By 2023 An. stephensi had crossed into Ghana and Nigeria, and had been found in 10 new sites in Kenya in 2023 and 2024. Evidence-based maps predict a high probability of presence within many urban cities across Africa. If An. stephensi breaks out from eastern Ethiopia into large cities (and Zanzibar) in the East African region could face malaria outbreaks of unprecedented size.

Of Resurgence and Elimination and Difficult Questions

The idea that a resurgence of malaria is a real possibility, that it has happened before to dramatic effect, and there are worrying indications of it happening in Zanzibar and elsewhere, is intuitively a very good argument that the global policy focus should be on final elimination. Blog 4 in this series discussed this issue in more detail and noted difficult questions that should be asked alongside reading this blog. Blog 3 demonstrated that Zanzibar needs to undertake more research to gain a much clearer understanding of the economic benefits that have been gained from malaria reduction and the implied benefits to investing more resources in holding onto to those gains or pushing further to complete elimination.