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Why don鈥檛 we make disease cures that are themselves infectious?

Tim Stevenson, Great Missenden, Buckinghamshire, UK

We do. They are called bacteriophages and were used medically in the Soviet Union. They are viruses that exclusively attack and live in bacteria. They only failed to become the go-to cure for many bacterial ailments because antibiotics are so easy to mass produce, whereas phages have to be sought out from the smelly places where they dwell, typically sewage.

There is an endless evolutionary struggle between phages and bacteria. This has a good and a bad side. The bad is that a continuous search for new phage cures is needed as bacteria develop stratagems to defeat them. The good is the potentially endless supply of different phage cures to set against our dwindling stock of antibiotics as resistance propagates among bacteria.

However, hopes of a bacteriophage cure that could sweep in on the tails of the current pandemic and stop it are doomed. Covid-19 is caused by a virus. Bacteriophages don鈥檛 parasitise viruses as these don鈥檛 have a metabolism to exploit.

Iain Brassington, University of Manchester, UK

I am in no position to say whether an infectious cure for a disease would be a practical possibility, but let鈥檚 assume that it would be. There would, however, be a serious ethical and legal concern about any such intervention because it would amount to unconsented medical treatment.

It is a widely accepted principle that people should be able to refuse medical treatment, even if it would be irrational to do so and even if there鈥檚 a public good to be served by giving it. But with a contagious cure, these people wouldn鈥檛 even get the chance to refuse, since they would be exposed to the 鈥渢reatment鈥� simply by standing next to the wrong person at the supermarket.

We do sometimes intervene medically without consent 鈥� we vaccinate babies, for example. However, even in that case, there is someone who could refuse on their behalf. There would be no such possibility with infectious cures.

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