But there have been other diseases that have confounded both scientists and the human body. An effective vaccine for dengue fever, which infects as many as 400,000 people a year according to the WHO, has eluded doctors for decades. In 2017, a large-scale effort to find one was suspended after it was found to worsen the symptoms of the disease.

Similarly, it’s been very difficult to develop vaccines for the common rhinoviruses and adenoviruses — which, like coronaviruses, can cause cold symptoms. There’s just one vaccine to prevent two strains of adenovirus, and it’s not commercially available.

“You have high hopes, and then your hopes are dashed,” says Nabarro, describing the slow and painful process of developing a vaccine. “We’re dealing with biological systems, we’re not dealing with mechanical systems. It really depends so much on how the body reacts.”