What does the Oxford Malaria vaccine mean for Asia?
Author: J Kevin Baird, Oxford University  The groundwork for the miraculously rapid development of COVID-19 vaccines actually began a few decades ago with basic research on molecular subunit vaccine technologies. In April 2021, the same researchers from the University of Oxford who developed the Oxford/AstraZeneca vaccine announced extraordinary findings with their experimental malaria vaccine R21/MM, which also uses subunit technology. Subunit vaccines employ a harmless fragment of an infectious agent to induce a protective immune response. For the R21/MM vaccine, scientists used an important molecular fragment in the malaria parasite species called Plasmodium falciparum and created virus-like particles to carry it. The antibodies and triggered immune cells that we form in response to the vaccine should, in theory, defend us against the living parasite in the wild. In April 2021, the developers published the results of an experimental trial of R21/MM in 450 infants and toddlers in Burkina Faso. During a year that included four jabs of the vaccine, the incidence of clinical malaria in children receiving R21/MM was 77 per cent lower than that in children who got a rabies vaccine instead. This is an unprecedented level of protection for any malaria vaccine and the first to exceed the World Health Organizations goal of 75 per cent efficacy. An earlier vaccine and technology used the same parasite fragments differently and its efficacy  in similarly exposed African children  was less than 40 per cent. While R21/MM still faces at least one more much larger trial to assess its safety and efficacy, the initial trial findings are exciting. R21/MM may substantially reduce child mortality numbers in Sub-Saharan Africa. But the new vaccine may have less direct relevance to the Asia Pacifics malaria problem for several reasons. First, the R21/MM vaccine is designed to reduce Plasmodium falciparum malaria mortality in young African children. While this malaria species occurs in both regions, the Asia Pacific has another important species, Plasmodium vivax, which the vaccination may not be effective against. Another version of R21/MM against vivax malaria is in the works but remains untested. Second, malaria in the Asia Pacific causes severe morbidity and mortality in all age groups, in contrast to Sub-Saharan Africa, where infants and toddlers are predominantly affected. Malaria mortality in the Asia Pacific occurs in lower numbers and among larger and more demographically diverse populations. It is harder to see and prevent. Vaccinating tens of millions of vulnerable children in Africa is both sensible and practical, but vaccinating all 2 billion people in Asia at relatively low risk of mortality is more challenging. Third, people infected by malaria parasites who are not experiencing any illness  thanks to natural or vaccine-acquired immunity  make controlling and eliminating endemic transmission more difficult. Most infected people in Asia carry malaria parasites without acute illness, infecting mosquitoes that go on to infect the relatively few people vulnerable to acute malaria. This occurs with chronic low-level exposure to malaria, which is typical of most malaria in Asia. In this setting, a vaccine that creates more silent carriers of malaria would make eliminating these parasites less likely. Nonetheless, a clinical trial of R21/MM in children and adults from Asia naturally exposed to malaria is needed to provide definitive evidence of its impacts on infection. The ideal vaccine for the task of eliminating the diverse malaria parasites from the Asia Pacific may look quite different to a vaccine like R21/MM. A vaccine for that task would need to offer protection not just from illness, but infection, so the vaccinated could not be carriers at all. This sterilising immunity is a tall order but scientists are in hot pursuit with another technology  live attenuated sporozoite vaccines  which may provide that protection. This kind of vaccination also proved effective across different species of parasites in laboratory animal models for malaria. A malaria vaccine ideally suited to the Asia Pacific would offer sterilising immunity against infection by any of the five species of parasites in the region that naturally infect people. Health officials could target the many pockets and scattered zones of active malaria transmission in Asia for vaccination. Interrupting the cycle of malaria transmission for only a few months could eliminate it, making vaccination a brief intervention rather than a lifetime enterprise  as it is with almost all other vaccines. Another type of vaccine  which prevents humans from infecting mosquitoes  is currently in development. These transmission-blocking vaccines would also help rid Asia of its malaria problem. Oxfords R21/MM could be a historic breakthrough for children in Africa, but it may have limited impacts on the elimination of malaria in the Asia Pacific. Asia is capable of reaching this goal, but it needs tools suited to its fundamentally different malaria problem. J Kevin Baird is Professor of Malariology in the Centre for Tropical Medicine & Global Health at the Nuffield Department of Medicine, University of Oxford, and Head of the Eijkman-Oxford Clinical Research Unit at the Eijkman Institute for Molecular Biology, Jakarta. first appeared on East Asia Forum. Source link