Imperial College UK Covid-19 Response Team report

This is worth reading, though slightly technical. Issued today, March 16, 2020. My takeaways on it below. But first, a quick illustration of the potential benefit of social distancing:

My key takeaways from the Imperial College report:

There are two strategies suggested:

  • mitigation
  • suppression

“Each policy has major challenges”. That means pluses and minuses. There is no magic bullet.

  • mitigation: ” slowing but not necessarily stopping epidemic spread – reducing peak healthcare demand while protecting those most at risk of severe disease from infection”
  • suppression: “reverse epidemic growth, reducing case numbers to low levels and maintaining that situation indefinitely.”

See that “indefinitely”? That’s one of the problems.

  • Mitigation.
    • the good news: “optimal mitigation policies (combining home isolation of suspect cases, home quarantine of those living in the same household… and social distancing of the elderly etc) might reduce peak healthcare demand by 2/3 and deaths by half.”
    • the bad news: “still result in hundreds of thousands of deaths and overwhelmed health systems (notably ICUs)”.
  • Suppression.
    • The good news: will require social distancing of the entire population + home isolation of cases + household quarantines + maybe school and university closures.
    • The bad news: “this will need to be maintained until a vaccine becomes available (18 months +) because transmission will quickly rebound if interventions are relaxed.
  • “China and S Korea show that suppression is possible in the short term. It remains to be seen whether it is possible long-term.”

The study makes use of knowledge and experience gained from the famous flu epidemic of 1918-19 (H1N1). Similarities include a global emerging disease epidemic with no access to vaccines. “In the US, measures adopted included closing schools, churches, bars and other social venues. Cities in which these interventions were implemented early in the epidemic were successful at reducing case numbers… and experienced lower mortality overall. However, transmission rebounded once controls were lifted.

The aim of suppression is to “reduce the reproduction number to below 1 and reduce case numbers or eliminate human-to-human transmission. The main challenge is that it needs to be maintained for as long as the virus is circulating…Furthermore, there is no guarantee that initial vaccines will have high efficacy.

Mitigation aims not to interrupt transmission completely but to reduce the health impact. A similar strategy was used by some US cities in 1918 and by the world generally in the 1957, 1968 and 2009 flu pandemics.

“The strategies differ in whether they aim to reduce the reproduction number, R, to below 1 (suppression) – and thus cause case numbers to decline – or to merely slow the spread by reducing R but not to below 1.

The impact of (these strategies) depends critically on how people respond to their introduction, which is highly likely to vary between countries… It is highly likely that there would be significant spontaneous changes in population behaviour even int the absence of government-mandated interventions.

“Suppression… carries with it enormous social and economic costs… Mitigation will never be able to completely protect those at risk from severe disease or death.”

The report presents results for the UK and the US, “but they are equally applicable to most high-income countries.”

Thanks to Karl Denninger of Market-Ticker for pointing me to this report. Denninger is not a medical man but a computer programmer and successful business man (retired) and someone who can do math (apparently a dying breed on this planet). His blog post on it includes these snippets:

“The native R is 3.0. If everyone socially distances we [in the U.S. – ed] don’t stop the virus, but we suppress the rate of growth… temporary R0 of 2.2.”

If you do nothing, the entire population of the US (330 million) is infected between 103 and 109 days. BUT (as Denninger points out), horrendous as that sounds and is, the virus burns itself out because immunity builds to 66% some time between days 121 and 127, “when that happens it can’t sustain transmission anymore.”

If suppression is implemented for 15 days (this is apparently what is being touted at the moment in the US) what happens? ” In 15 days nothing happens.  At all.  If you drop the restrictions in less than approximately six months you’ve accomplished nothing. 

The other downside is that the % of immunity hardly rises at all, reaching a bare 10% after 169 days (5.5 months).

“You’re talking three months of active suppression (assuming we’re already three months into it) and this assumes we are going with an R0 “suppressed” of 2.0.  Note that 2.0 only drops the load in the medical system by about a third, which is probably not enough.

” If you hold the suppressed R0 to 1.3 (approximately seasonal flu) you now have to hold these policies, … for six months, not three.

“In fact, …you likely would have to hold these policies for anywhere from six months to a full year, depending on where we manage to clamp R0 at.  If you let the measures go early everything you did is laid waste as any release of those measures prior to achieving immunity of approximately 40% still overloads the medical system when you drop the restrictions.

“This cannot work folks.

“We must instead look at mitigating steps so those who are high risk do not become hospital admissions.  We won’t get them all, but we must get enough of them to prevent an overload.  If we do that this is over in four months and the economy survives.

He shows the numbers on his blog and you can see the table there.

In an earlier post, he wrote, “

 You are going to get this bug.  That’s odds-on.  70%+ between now and when we have an effective vaccine that can be mass-administered if that ever happens, which it might not. There’s simply no way around this.”


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