KVA
25th April 2022
Vicky Smith, Associate Medical Writer

A vaccine for malaria: what does it mean for the future?

Malaria is a preventable and treatable disease. Despite this, malaria killed more than 629,000 people worldwide in 2020. Of these, more than two thirds were among children under the age of 5.1

Malaria has a devastating impact on the health and livelihood of people around the world. It is a parasitic disease characterised by mosquito transmission and is found in mostly tropical and subtropical climates. Infected Anopheles mosquitoes transmit the parasite, of the genus Plasmodium, which then enters the victim’s blood, travels to the person’s liver and reproduces. Plasmodium falciparum has the highest associated rate of human morbidity and mortality, and therefore represents a major public health threat in areas where malaria is transmitted.2

Historically, this disease has chiefly been treated using drug treatments and insecticide-treated bed nets as a preventative measure to reduce spread. Issues of drug resistance are well reported, and current drug-based treatment options are not viable long-term.3 However, in a historical moment, on October 6th 2021, the World Health Organisation (WHO) announced they were backing the four-dose malaria vaccine, RTS,S/AS01, and recommending its widespread use among children living in areas of sub-Saharan Africa with moderate-to-high transmission rates.4 RTS,S is the first parasite vaccine to have obtained regulatory approval.5

The RTS,S vaccine consists of a segment of the circumsporozoite (CSP) protein from the parasite P. falciparum which has been bound to part of a second protein, taken from hepatitis B virus.6 While CSP alone will not be recognised by the immune system, the hepatitis B viral protein helps the immune cells recognise the vaccine protein as foreign and allows for the immune system to generate a response against the malaria CSP protein. An immune response against CSP will then prevent the invasion of the parasite into hepatocytes, along with targeting infected hepatocytes for destruction.2

While most readily available vaccines have very high efficacy rates (for example, the Covid-19 vaccines have efficacy rates of 60–90% against severe disease), the RTS,S vaccine showed efficacy of only ~30% against severe disease, and the level of protection wanes over time.6 However, the vaccine was shown to be cost effective and the recent recommendation from the WHO will likely increase access to malaria prevention tools; prediction modelling suggests that this new guidance could prevent the death of up to 23,000 children a year if given to children in countries with high incidence of malaria.7

Compliance and acceptance rates are high, despite the complex requirements of the vaccine (four separate doses are required for full effect), and target countries are receptive to implementing the vaccine rollout, even where they are lacking the full resource.5 The threat of resistance for this parasite-targeting vaccine is very real, and no single tool that is available today will be able to solve the problem of malaria.1 The vaccine will be implemented alongside existing prevention methods, including nets and insecticides to ensure a multi-pronged approach to preventing the spread of malaria.

Moving forward there is hope. A subset of countries with a low burden of malaria are quickly moving towards disease elimination; zero malaria is becoming an achievable goal. China and El Salvador joined 38 other countries in becoming certified as malaria-free in 2021.8 There are numerous ongoing investigations into new vaccine targets, vector control approaches and antimalarial medicines and innovation is at the forefront of malaria treatment.

References:

  1. WHO. World Malaria Day 2022. Available at: https://www.who.int/campaigns/world-malaria-day/2022 (accessed April 2022).
  2. Laurens MB. Hum Vaccin Immunother 2020;16:480–489.
  3. Kozlov M. Nature 2021;597:604.
  4. WHO. WHO recommends ground-breaking malaria vaccine for children at risk. October 2021. Available at: https://www.who.int/news/item/06-10-2021-who-recommends-groundbreaking-malaria-vaccine-for-children-at-risk (accessed April 2022).
  5. The Lancet. Lancet 2021;398:1381.
  6. White MT, et al. Lancet 2015;15:1450–1458.
  7. Hogan AB, et al. PLoS Med 2020;17:e1003377
  8. Countries and territories certified malaria-free by WHO. June 2021. Available at: https://www.who.int/teams/global-malaria-programme/elimination/countries-and-territories-certified-malaria-free-by-who (accessed April 2022).