Over the past several weeks, I have spent a considerable amount of time fielding requests from people wanting to know if I think the lack of new cases of the deadly virus that claimed the lives of 172 people in 2017 will lead to a decrease in the number of people affected by it. They wonder whether the incurable virus will return in the most infected countries. At first, my answer was the same as it always is: that there is no evidence that it will.

In places where there was heavy virus transmission last year — Yemen, Haiti, Democratic Republic of the Congo, Uganda, Guinea, Nigeria and Sierra Leone — and other countries where it has emerged (such as Eritrea and Ethiopia) there have been no reported cases of the virus for some time. There is no evidence the virus will return. If it did, all those countries would suffer unprecedented levels of cases, because their viral responses and immune responses would be markedly different.

Nor is there evidence that cases of illness will decline because of use of ritually prescribed medicines. These medicines are usually used for specific diseases, such as multiple sclerosis or typhoid fever, and appear to have no impact on the virus. Their ability to harm the immune system also raises the potential for increased therifeicide. The first of these arguments was made by Dr Alexander Tompkins, a U.S. expert on the SARS virus. His analysis is being published this week.