The COVID lockdown

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Shall I mention herd immunity?

Approximately 90-95% of the population needs to be infected with COVID-19 before herd immunity is achieved. China, Germany and Italy have been mass testing in feverent hope of this happening. Their have been the obvious set backs – lack of testing kits for one, and then the logistical issues; not being able to do the number of daily tests needed to capture the 60 million – 1.4 billion strong population in these countries (realistically speaking this would take years rather than months). There is also speculation whether exposure in fact means immunity, with reports of second positives being reported on a monthly basis.

Scientifically speaking in the absence of herd immunity, isolation procedures or lock down must continue. A resurgence in the number of death rates to speed up this process is a highly unlikely proposition. Every politician out there would therefore be looking at ways to make this more palatable to their constituents. My local library that belongs to a consortium of libraries in the UK called the ‘Idea Store’ is a good litmus test when it comes to such matters. At the start of lockdown, my book loans were automatically renewed till the end of April, but as of today this has been extended to July 1st. I could have sworn that the current dictum is lockdown for a further three weeks.

The UK Foreign secretary Dominic Raab as of four days ago

As the NY Times says in its opinion piece, this is lockdown with no clear exit strategy: https://www.nytimes.com/2020/04/16/world/europe/uk-coronavirus-lockdown-exit.html.

Maybe they all missed this seminal paper in the Science Magazine on the exit strategy:

Abstract on how to mitigate the possibility of resurrgences of COVID-19 infection

The bottom line is that intermittent or prolonged periods of social distancing/lockdown may be needed to mitigate the resurrgence of infection. They base their conclusions on the following principles:

  1. ‘After the initial pandemic wave, SARS-CoV-2 might follow its closest genetic relative, SARS-CoV-1, and be eradicated by intensive public health measures after causing a brief but intense epidemic’ – this scenario is considered unlikely.
  2. ‘Alternatively, the transmission of SARS-CoV-2 could resemble that of pandemic influenza by circulating seasonally after causing an initial global wave of infection’.

The pandemic and post-pandemic transmission dynamics of SARS-CoV-2 will depend on factors including the degree of seasonal variation in transmission, the duration of immunity, and the degree of cross-immunity between SARS-CoV-2 and other coronaviruses, as well as the intensity and timing of control measures

So what are our potential outlooks?

One-time social distancing scenarios in the absence of seasonality.

(A to E) Simulated prevalence of COVID-19 infections (solid) and critical COVID-19 cases (dashed) following establishment on 11 March 2020 with a period of social distancing (shaded blue region) instated two weeks later, with the duration of social distancing lasting (A) four weeks, (B) eight weeks, (C) twelve weeks, (D) twenty weeks, and (E) indefinitely. There is no seasonal forcing; R0 was held constant at 2.2. The effectiveness of social distancing varied from none to a 60% reduction in R0. Cumulative infection sizes are depicted beside each prevalence plot (F to J) with the herd immunity threshold (horizontal black bar). Of the temporary distancing scenarios, long-term (20-week), moderately effective (20%-40%) social distancing yields the smallest overall peak and total outbreak size.

One-time social distancing scenarios with seasonal transmission.

(A to E) Simulated prevalence, assuming strong seasonal forcing (wintertime R0 = 2.2, summertime R0 = 1.3, or 40% decline), of COVID-19 infections (solid) and critical COVID-19 cases (dashed) following establishment on 11 March 2020 with a period of social distancing (shaded blue region) instated two weeks later, with the duration of social distancing lasting (A) four weeks, (B) eight weeks, (C) twelve weeks, (D) twenty weeks, and (E) indefinitely. The effectiveness of social distancing varied from none to a 60% reduction in R0. Cumulative infection sizes are depicted beside each prevalence plot (F to J) with the herd immunity threshold (horizontal black bar). Preventing widespread infection during the summer can flatten and prolong the epidemic but can also lead to a high density of susceptible individuals who could become infected in an intense autumn wave.

Intermittent social distancing scenarios with current and expanded critical care capacity.

SARS-Cov-2 prevalence (black curves) and critical cases (red curves) under intermittent social distancing (shaded blue regions) without seasonal forcing (A and C) and with seasonal forcing (B and D). Distancing yields a 60% reduction in R0. Critical care capacity is depicted by the solid horizontal black bars, and the on/off thresholds for social distancing are depicted by the dashed horizontal lines. (A) and (B) are the scenarios with current US critical care capacity and (C) and (D) are the scenarios with double the current critical care capacity. The maximal wintertime R0 is 2.2 and for the seasonal scenarios the summertime R0 is 1.3 (40% decline). Prevalence is in black and critical care cases are in red. To the right of each main plot (E to H), the proportion immune over time is depicted in green with the herd immunity threshold (horizontal black bar).

It’s a toss up between which strategy each nation would ultimately choose. My question is whether vulnerable individuals, including those on immunosuppressants should isolate into early Oct or April the following year based on the above assumptions of one time isolation or intermittent social distancing?

What do you think?

About the author

Neuro Doc Gnanapavan

22 comments

  • A five year old little girl died from Corona virus covid-19 in Detroit, Michigan this weekend her mother is a Detroit police officer her father and area firefighter. A little girl had been on a ventilator for 2 weeks with the covid-19 she developed meningitis her brain swelled and she died. A seven-month-old infant in North Carolina had been infected with covid-19 about a month ago but he is okay now however 10 days or so ago in Denver a 13 year old with intractable epilepsy who started the use of Charlotte’s Web marijuana for her seizures also died of covid-19 at the age of 13 years old. A young girl aged 12 located in New Orleans Louisiana had been on a ventilator for a couple weeks and I do not know how she has fared at this point. Meanwhile within the past couple days it was reported that a two year old little boy also I believe in North or South Carolina not certain was hospitalized with a temperature of over 107 degrees in the emergency department the doctor’s got his temp lowered to about 104 they weren’t sure he was going to survive but as of the last report he was doing much better but again two years of age. Meanwhile a 29 year old man with no pre-existing health conditions was not expected to live his family gathered at the hospital and through a glass window he was given last rites she had been on a ventilator for over two weeks but he did pull through so this is affecting younger people including infants toddlers and other children.

  • Assuming a R naught of 2-2.6 for SARS CoV-2 then roughly 60% of the population would need immunity before the spread of the disease reaches stasis. Measles, with an estimated R naught of 18 requires 95% immunity in the population to stop the spread. How did you arrive at the value of 95% immunity for SARS CoV-2? Secondly, although there is no data on cross immunity between the betacorona viruses it seems that if there was a vaccine for CoV-1, MERS then it would have reduced the spread of the CoV-2…..presumably. Even an influenza vaccine that is only 50% effective is better than nothing. It seems that the research community focusing on emerging infectious diseases were somewhat short-sighted in this regard. Lastly, a highly sensitive and specific EIA is needed for reliable longitudinal immunity.

    • Steve, the R0 estimates of between 2 and 3 for SARS-CoV-2 were done with symptomatic cases that were PCR positive. With it looking like 25-50% of people having an asymptomatic disease and being able to spread and the fact that the nasopharyngeal PCR has a sensitivity of ~75% the true R0 for SARS-CoV-2 is likely to be in the order of 5-7.

      Common sense says it has to be higher than 3 simply by looking at the rapidity of the spread of COVID-19 across the globe and the data we have from superspreaders.

      I, therefore, think that for herd immunity we are going to need at least 80% (R0 = 5) and probably closer to 86% (R0 = 7 – my estimate) of the population to be immune to get herd immunity.

      It is also going to be difficult to get accurate R0 estimates now as social distancing and other behaviours reduce the R0 artificially and when these are relaxed transmission will commence once again.

    • “ It seems that the research community focusing on emerging infectious diseases were somewhat short-sighted in this regard. ”
      Probably has more to do with government funding “priorities” being short sighted, rather than the researchers, most researchers in the field have been saying that eventually there would be a viral pandemic, but after a short burst of funding for SARS and MERS, funding got cut too soon, because in the usual short-sighted way of governments the threat hadn’t eventuated…. time to spend money on something to win votes.

  • None of the variables are modelling for cross border (re)transmission. A better question to ask would be if you were highly vulnerable and non-suicidal, why the hell would you venture out of your cocoon in an open border society?
    Testing and herd immunity figures in your community or society are irrelevant when someone from Afghanistan flies over.
    Best bet surely is to stay safe until vaccinated, whenever that date is. Lets not confuse a mostly laymen readership with charts and large data sets.

    On a seperate note, what is low B-cell clone in the context of patients receiving natalizumab please?

    • Yes there is that. If all the countries adopt the same lockdown policy then an open border doesn’t matter so much. If however one country has a stricter lockdown policy then people living there would over time be at greater risk than countries with less stringent lock downs. Air travel is a major problem, but can be overcome if you quarantine for a week at arrivals for all with testing of all passengers. I suspect as governments discuss this more and more these policies may come into effect.

      With regard to Bcells and natalizumab it’s important if the regulatory B cell entry in the brain is heavily impacted. But T cells equally important as we already know from PML risk

    • What do you see as highly vulnerable? Unless you are truly high risk (advanced age with multiple comorbidities), waiting until a vaccine is available seems not like a worthwhile tradeoff for most – for financial, social and, last but not least, medical reasons.

      Having said that, I am still waiting for now (my area is ahead of the UK if I look at the curves).

        • Let’s hope you are right, MouseDoc (assuming active means safe and effective), as it could somewhat alleve a significant crisis of confidence among the population, and be a bridge to a vaccine. Remdesivir, perhaps, although probably has to be administered early in disease course. Fingers crossed for safety and efficacy for Favipirivir, Atazanavir or Leronlimab. All early days for those. Regarding vaccines, and perhaps even with antivirals, FDA and other regulatory agenices may be forced to permit “challenge trials.” Do you have an opinion on such trials?

          • There is news circulating about some antivirals, but we have heard this before, You are absolutely right. In my opinion the anti-virals are being used too late.

            As for Challenge trials where you infect people could be a scary one, maybe they will select a non virulent variant but if the price is right some young people will take the risk for the cash. As an old fart it would rather scare the SH1 out of me with a 1-5% death rate would you be willing to draw the short straw. But at 0.5% you say “Piece of Pi*s” you run this risk with HSCT all the time.

            Maybe ask ProfG, you could vaccinate health care workers and see how many dont get infected

      • Those considered highly vulnerable by each speciality would differ. For neurology there is a list. In MS those on heavy maintenance immunosupression. I will be using lymphocyte subsets, immunoglobulin levels to direct this. In those who have had COVID19 already, did they require ITU admission (or severe symptoms) would be another factor – time is needed for lungs to recover. This list will not be large.

  • Impossible to have to stay isolated until October, April etc etc. Massive effect on mental health and huge effect on livelihood. I just don’t see how it can be an option (obvious exception is those who want to do it).
    I’ll have to get off my DMT if that is the only option I can’t stay in forever!

    • I’m grateful for the CoVid19 posts. This blog (because of the potential impact on the MS community) is the best pool of scientific info we have.

      Is it possible to share this post, with permission, on social media?

    • This is a legitimate concern. It is a matter of who, rather than if we can do it. It will also test of weather we can do things differently including work and travel, and organisation of our day. Having said all this, this all pales in comparison to the number of lives that will be lost by the end of this. If we plan knowing this piece of information we will reduce the ultimate number, ignoring it may send us straight back to square one. For example, we already know that intermittent lock down leads to a sudden resurgence in figures from Hong Kong and South Korea – so this is not entirely just hypothesis based.

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