” If enough people develop an immune memory of a new disease, it stops spreading, even if part of the population is not immune. This is herd immunity: it is effective, but it is typically only seen as a preventive strategy in vaccination programs. In this case we do not have a vaccine and obtaining herd immunity would require a significant portion of the population to be infected with COVID-19 and then heal.
The percentage of the population that must be immune to allow herd immunity depends on how transmitted a disease is, which is measured with R0, the number of new infections each case generates. For COVID-19, R0 is estimated at 3,28, but studies are still ongoing and this number will probably change. So in order to have herd immunity, about 70 % of the population of the UK should be immune to COVID-19. To get there, more than 47 million people would need to be infected. According to current estimates, COVID-19 has a mortality rate of 2,3 % and a serious illness rate of 19 %. Achieving herd immunity at COVID-19 in the UK could cause deaths of more than 1 million people with another 8 million serious cases requiring intensive care.
Even if we manage to protect the most vulnerable people (and still don’t say how to do it and for how long) the mortality rate for the otherwise healthy population could still be 0,5 % or higher. This means that even in this “best” but unlikely scenario we would still face more than 236.000 deaths.
Waiting for herd immunity to develop at COVID-19 is not a good public health strategy. We can and must do better “.
Jeremy Rossman, Honorary Senior Lecturer in Virology and President of Research-Aid Networks, University of Kent.