SARS was very unusual, and serves as a partial counterexample. On the other hand, the “trend” being shown is actually almost entirely a function of the age groups of the people infected—it was far more fatal in the elderly. With that known now, we have a very reasonable understanding of what occurred—which is that because the elderly were infected more often in countries where SARS reached later, and the countries are being aggregated in this graph, the raw estimate behaved very strangely.
SARS was very unusual, and serves as a partial counterexample. On the other hand, the “trend” being shown is actually almost entirely a function of the age groups of the people infected—it was far more fatal in the elderly. With that known now, we have a very reasonable understanding of what occurred—which is that because the elderly were infected more often in countries where SARS reached later, and the countries are being aggregated in this graph, the raw estimate behaved very strangely.