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Covid-19 is not flu. It is caused by a virus, Sars-CoV-2, about which relatively little is known, and some of the experimental vaccines currently going through clinical trials also make use of novel technology. That is a lot of unknowns. We dont have a vaccine for any coronavirus, so why do people assume this is going to be straightforward? Dawson asks.

One potential risk with some kinds of vaccine, for example, is that they can cause the recipient to experience a worse bout of the disease if that person becomes infected naturally later on. This phenomenon, known as antibody-dependent enhancement (ADE), has been a problem with experimental vaccines against severe acute respiratory syndrome (Sars) which is caused by a virus related to Sars-CoV-2 and it will need to be ruled out by rigorous testing of vaccines against Covid-19.

If ADE were to turn out to be a problem with a vaccine after it had been approved, in a country with poor safety reporting, years might pass before the full human cost came to light. This is a dilemma currently exercising the Africa Centres for Disease Control and Prevention, which is working with Covid-19 vaccine developers to set up phase 3 trials in Africa. Covid-19 outbreaks are now growing in parts of that continent, meaning it is potentially a good place to test the ability of a putative vaccine to protect people against infection, but safety surveillance can be patchy there. Often where you have most cases of an infectious disease, the infrastructure for surveillance isnt as good, says Kampmann.