Some viruses are similar enough that just one vaccine is needed to treat them all.
There's no scientific definition for a wave of disease – and no evidence that the original onslaught of coronavirus in the US has receded much at all.
The Lagos state government must go beyond food packages as stimulus, and build capacity for poor people.
The federal government has announced a stepped approach to relaxing social distancing measures. What they haven't said is how high they'll allow the curve to rise.
The science is far from certain, but it appears at least a proportion of people who have had COVID-19 will be protected from another infection – at least initially.