Monday, October 11, 2021

The malaria vaccine's lessons for COVID-19

 - Jennifer Middleton, MD, MPH

Last week, the World Health Organization (WHO) endorsed the use of RTS,S (Mosquirix), a vaccine against malaria which targets Plasmodium falciparum in its sporozite phase. Mosquirix, given in 4 doses between ages 5 months and 3 years, is the first vaccine ever developed against a parasite. Plasmodium falciparum's range is limited to Africa, and the distribution of RTS,S will be appropriately prioritized to areas of greatest need there

RTS,S decreases the risk of severe malaria by 50% in the first year, though its effectiveness wanes to near zero after 3-4 years. Combining RTS,S with seasonal chemoprophylaxis further improves outcomes:

There were 305 events of uncomplicated clinical malaria per 1000 person-years at risk in the chemoprevention-alone group, 278 events per 1000 person-years in the vaccine-alone group, and 113 events per 1000 person-years in the combination group. The hazard ratio for the protective efficacy of RTS,S/AS01E as compared with chemoprevention was 0.92 (95% confidence interval [CI], 0.84 to 1.01), which excluded the prespecified noninferiority margin of 1.20.

Worldwide, malaria afflicts over 220 million people a year; in Africa, it kills an estimated 400,000 persons a year. Children bear its brunt, with 67% of malaria deaths occurring in children under the age of 5 years, and it causes profound morbidity in those who survive (and are often repeatedly reinfected). RTS,S will not singlehandedly eliminate malaria, but, in combination with bed nets and chemoprophylaxis, it could help prevent over 5 million cases of malaria - and over 23,000 child deaths - a year. 

RTS,S and the COVID-19 vaccine share some interesting parallels. The COVID-19 vaccines are also not 100% effective at preventing COVID-19 disease, but they have still saved hundreds of thousands of lives since their introduction as well as reducing the morbidities associated with COVID-19 infection. In combination with face masks and social distancing, the COVID-19 vaccines can provide a path out of the pandemic. Prioritizing COVID-19 vaccine supply to regions of the world still waiting for their first doses (instead of focusing on boosters for those already vaccinated) could maximize their life-saving capacity and reduce the risk of further viral mutation. Viewing these infectious diseases as complex, global challenges that require a multifactorial approach could lead to more effective collaboration, cohesive solutions, and more lives saved. 

In the meantime, we need to keep recommending COVID-19 vaccination as well as discuss preventive measures with patients planning travel to malaria-endemic regions. This AFP article on "Prevention of Malaria in Travelers" provides an overview of medications, insect repellents, and bed nets, and the Centers for Disease Control and Prevention (CDC) has additional information on malaria diagnosis and treatment. The AFP By Topic on Travel Medicine also includes this article on pretravel consultation along with a wealth of patient education handouts.