Thread by @_MiguelHernan

Europe and US in total or partial lockdown to mitigate #COVID19.

Soon more hundreds of millions will be confined to their homes. Huge personal sacrifices. Staggering economic losses.

Ok, we accept the price for the common good. But how does this end? Here are some strategies:

1) Develop a vaccine and vaccinate.

If a sufficiently high % of the population is vaccinated and becomes somewhat immune, this “herd immunity” lowers the probability of transmission to a susceptible person until the epidemic dies out.

Ideal but unlikely to happen soon enough.

2) Lift lockdown (after curve flattens) and let the epidemic run its natural course without protective measures.

This brings back the scenario that lockdowns are trying to avoid: millions of people dying without adequate medical attention in overrun health systems.

A no-no.

3) Lift lockdown (after curve flattens) and try some social distancing + containment again.

If this strategy fails, a second lockdown is needed. We enter a cycle of lockdowns until a sufficiently high % of people becomes infected.

Not economically and socially sustainable.

4) Stratified lockdown.

The lockdown is lifted ONLY for households whose members are all healthy individuals under 50 years of age. Large gatherings and travel are encouraged, handshakes and kisses return, schools/universities and businesses reopen with the available staff….

The goal is to get as many healthy children and young people infected as possible to build "herd immunity".

Households with older people remain confined without contact with friends and family. Children in those places may move in with family members so they don't miss school...

Over time, as herd immunity increases, lockdown is progressively lifted for older people.

Lots of details to be worked out, sure, but a sound #stratifiedlockdown wouldn't collapse health systems. Each country would establish the threshold age based on its national capability.

Obvious question: why not start directly with a stratified lockdown, as the UK plans to do? That train has left the station for much of the world (perhaps even the UK).

Also, even going through a complete lockdown is tough, there's a bright side if a #stratifiedlockdown follows:

After a complete lockdown, people understand that the stakes are high and societal structures are already in place.

Most of us will be proud to cooperate with a #stratifiedlockdown: people outside will do their part by getting infected and people inside by not getting infected.

A #stratifiedlockdown is more fair. It puts more burden on the population group that obtains the greatest benefit

A stratified lockdown is likely more sustainable. The societal and economic costs of a stratified lockdown seem lower than alternatives.

Modelers, model it please.

Thanks to all who sent comments about pros and cons of a #stratifiedlockdown.

Two serious concerns are
1. Practical implementation
2. Scientific uncertainty regarding
a. immunity to #COVID19 #coronavirus
b. disease severity in younger people

Let's take each at a time.

The practical implementation of a #stratifiedlockdown involves complex logistical issues, but not more complex that those required by the full lockdown now in place.

If we start planning now, societies will be more ready to understand/adhere when their participation is needed.

What if people don’t develop any form of immunity to the #COVID19 #coronavirus?

Possible but unlikely.

Evidence suggests that immunity for the 4 endemic coronaviruses (which are a cause common cold) is longer than for flu, and that re-infection results in milder disease.

What about severe cases in younger people?

A #stratifiedlockdown wouldn't work if hospitalizations among still susceptible younger individuals collapse health systems again (or if many get lung damage or die).

Current data suggest this wouldn't be the case, but need more data.

Of course, a #stratifiedlockdown could be the preferred option if an effective treatment emerges soon.

Regardless, it isn't too early to start preparing societies in lockdown for the next step. Before personal and economic costs of extreme social distancing become unacceptable.