¿Debemos reconsiderar la inmunidad de la manada?

Inmunidad del rebaño y propagación de la enfermedad en la comunidad o población inmunizada con personas infectadas como virus contagioso que se extiende en la sociedad en un estilo de ilustración 3D.

No product launch in history was botched as badly as herd immunity.  Introduced to the public, it enjoyed a short life before being pronounced dead and buried by the Sunday morning news shows.  First impressions last, and for most people hearing of the concept for the first time, its reputation was irrevocably tarnished.

Inmunidad de la manada

But its portrayal as an irresponsible, heartless policy to allow the disease to rampage indiscriminately through the country could not be more inaccurate. Herd immunity has kept the human species alive for two million years. In the absence of a vaccine, herds (or populations, if you prefer) do not get wiped out by new viruses. Natural barriers are formed within the herd that contain and deprive the virus of space to expand. Herd immunity is not a policy choice, in that it can’t be rejected and put back on the shelf. It will happen eventually, regardless of the interventions we make. It is a human conceit that we can control natural processes. Instead, rather like a martial art, the question is how to channel herd immunity to counter the virus.

As Dr David L Katz argued in his New York Times article ‘Is our fight against coronavirus worse than the disease‘, the specific profile of COVID-19 lends itself to a herd immunity approach. Lea aquí.

Opciones políticas

The data “clearly points to clear and important risk differentials for severe coronavirus infection…based on age and prior health”. Unlike influenza, it does not kill children, meaning there’s very little risk of exposure for one of the most vulnerable groups in our societies. In the absence of a vaccine, a strategy of shielding the vulnerable, while allowing herd immunity to build amongst less vulnerable groups, can minimise the aggregate of direct and indirect costs. The current obsessive focus on a single metric –the number of deaths of people with COVID-19 – is counter-productive as it’s an incomplete measure of the true costs and benefits of policy choices. The impact on public health outcomes of poverty, lack of access to healthcare and basic services, will also have a massive, and currently unmeasured, effect. Katz proposes that policy choices should be based on “total harm minimisation”.

Swedish Professor Johan Giesecke, the first Chief Scientist of the European Center for Disease Prevention and Control, goes further. In a scathing interview, he challenges not only the assumptions behind Imperial College’s model and the UK policy choices based on that model, such as closing schools, but argues that the virus amounts to a “tsunami of a usually quite mild disease” that will wash over Europe regardless of the lockdown, with at least half of the population becoming infected.

Visión holística

Public health policy choices by individual countries will, over time, have little impact on the number of deaths, but the costs of the lockdowns will far exceed those of a targeted strategy to protect the most vulnerable.  Giesecke goes further than Katz and considers the political as well as the economic costs, citing how Viktor Orban in Hungary has used the virus to suspend normal parliamentary democracy. (Our own Government isn’t far off doing that, either.) In an article from April 20th in China’s state propaganda organ Global Times, China clearly signals how it would like the crisis to end. It is entitled ‘Divisive US politics leads to democracy’s fast decay’. Lea aquí.

It has now been six weeks since herd immunity was rejected, but it’s been happening in the background nonetheless. As Professor Ioannides of Stanford University has recently reported, based on serological tests for the presence of antibodies, the actual infection rate in the population may be 50 – 85x higher than the number of documented cases.

The problem the UK now faces is how to quietly return to this strategy without alarming the public, having rejected it once for being too dangerous. Only with a holistic view of the costs and benefits of different policy choices we can make sensible decisions.