Herd immunity is impossible without a vaccine

We will win this war through immunity. Understanding immunity to respiratory viruses is really difficult — more like decoding Enigma than developing radar. We will need new technology as well as optimizing existing tests. So far, the best tests can give a reasonable estimate of whether someone has been exposed to the virus. They cannot yet tell you if you are immune to it. The trouble with coronaviruses is that they have evolved to evade immunity. They possess all sorts of unknown weaponry that dampens down our immune responses.

Humanity has never developed ‘herd immunity’ to any coronavirus, and each of the four ‘seasonal’ coronaviruses that we’ve all had in childhood (and subsequently) can re-infect us throughout our lifetime. This was experimentally demonstrated for the seasonal coronavirus strain called 229E, which usually causes a mild infection — just like Sars-CoV-2 does in the majority of cases. Volunteers were infected with 229E, and duly developed symptoms. They also developed antibodies a couple of weeks later. They were then able to be re-infected a few months later (albeit they developed milder symptoms). So far there are no confirmed cases of reinfection with Sars-CoV-2, but the virus has been with us a very short time (yes, I know it feels like an age). My prediction would be that for patients who have only mild, or indeed no, symptoms of COVID-19, they will probably not develop a strong and lasting enough immune response to prevent reinfection in several months’ time.