Officials are celebrating the first effective malaria vaccine, a project 30 years in the making. The vaccine, known as Mosquirix, comes with many caveats. For one thing, it is only effective in children ages 5-17 months, not newborns or adults, and even then only reduces infections by 1/3. It must be administered in 4 shots on a schedule that does not align with regular childhood vaccinations, meaning much higher administrative costs and complexity. The price is unknown, although its developer has vowed to sell it at cost. Despite all the uncertainties, researchers are still celebrating Mosquirix as a breakthrough, understandable given the arduous history of malaria vaccine research.
Unlike most common illnesses, malaria is caused by a parasite, not a bacteria or virus. A malaria vaccine has proven devilishly difficult to develop due to the lifecycle of the malaria parasite, Plasmodium falciparum according to PNAS. P falciparum has a very complicated lifecycle in the body, moving from the blood to the liver and back to the blood as it develops (illness occurs in the second blood stage). Survivors of repeated bouts of malaria can develop immunity to malaria, but the immunity occurs at a particular stage of the parasites cycle and which stage is not the same in every immune survivor. Given the lack of a uniform immune response, studying survivors has been of limited use in developing an inoculation. As such, years of research needed to be devoted simply to understanding the different life stages of P. falciparum.
Vaccines work by exposing the immune system to a version of a pathogen, stimulating the development of antibodies that recognize particular proteins in the pathogen. The antibodies lead the immune system to target and destroy those proteins, eliminating the threat. That means that in a complicated case like malaria, it is not enough to map out its lifecycle, particular proteins must be identified at each stage of the lifecycle that might make viable targets for antibodies. In practice the search for a malaria vaccine has really been the search for multiple components that might be combined into a vaccine. The PNAS article was written in 1999, so it still took another 15 years after most components of the malaria life cycle were identified to produce a viable vaccine.
Given the history, no wonder researchers are excited about Mosquirix. Hundreds of thousands of children die annually from malaria, so even a third of that translates to many lives saved. Mosquito prevention measures such as bed nets are cheaper, but vaccines cannot be diverted for use as fishing nets (it happens a lot), and are less ecologically harmful than mosquito spraying.
Mosquirix may not be perfect, but it might be a bridge to something more effective. Eliminating malaria will be a multifaceted task, and a vaccine will be a key part.