Covid-19 – collection of facts

Argumentations of Facebook tend to go around in circles, and new people join who didn’t read the previous messages which makes everything totally confusing. For this reason I will here try to summarise what I believe I know with relevant references.

Links

What is it?

SARS-Cov-2 is a virus of the Corona family, that causes the disease Covid-19

How does it spread?

WHO says “… spreads primarily through droplets of saliva or discharge from the nose when an infected person coughs or sneezes, so it’s important that you also practice respiratory etiquette (for example, by coughing into a flexed elbow).”

A virus can infect people who are not immune. Immunity can be obtained in two different ways; through vaccine and through having the disease.

Who gets sick and die from it?

Anyone can get sick. If you are exposed you can be sick.

A portion of this getting sick, need medical attention. A portion of this need ventilators a portion of these full ICU. And a portion of these infected will die.

Looking at a snapshot of the Swedish statistics it’s appears to be more common the older you get. Given that Sweden’s population growths, not only by immigration but also by births and by the fact that the older you get, the more in each age group has already died. This means that the number of cases is quite uneven from the general population in the respective age groups. What is quite clear is that mortality is drastically higher with age.

Spreading scenarios

Background

If you haven’t seen this – DO watch it!

It explains the inflection point, when the growth factor is under 1 and things are slowing down. And it also explains why small changes ins spread can make a huge impact.

1) Untamed spreading

This means that nothing at all is done and the virus can spread like wildfire. Depending on how contagious the virus is, it spreads until a point where immunity kicks in and there are no real new people to be infected. This exponential growth is like a pyramid game, which collapses when there are no new targets.

One can argue that this is natures way, but humans tend to want to minimise mortality. This scenario has one clear effect that causes avoidable deaths and that is that the number of cases grows so fast that the health care system will inevitably collapse under the pressure of the new cases. No country could be prepared for a population of which a percentage need medical attention, and a portion of this also will need ICU. No country has that sort of ICU capacity.

2) Managed spreading

Keeping the spread down to ensure that the medical system can cope seems to be one of the prevalent strategies. This is known as “flattening the curve”.

Tools for mitigating spread is in a separate section.

Please mind that the “area under the curve” – the integral – is the same. The spread will still propagate until you reach the inflection point, wherafter the spread will slow down until it’s reached all it can reach and fade out so if you manage to press the curve down, it will last longer.

The fastest way to allow the disease to get to the point where it can no longer spread, with a minimal mortality, is to ensure the spread is below the capacity of the health care systems maximum (passing this limit will cause avoidable mortality), but not too much under the capacity as this will mean the mitigation tools must me in force longer that needed.

And please mind – in this scenario you want a little bit of spread. Not too much and not too little. A perfect time for the Swedish word “lagom”, which means just that. Not too much and not to little.

3) Eliminate spreading

In the very early phases of spread, you only have import cases. In this phase one can try to find the cases and do contact tracing with the ambition to find all cases and take them out of circulation for totally eliminating the spread.

This is a valid tactics for very early phases when you don’t have a general spread. Some countries have managed this tactics, like New Zealand.

Some reflections;

It’s a lot easier for island countries to execute this tactics as the borders are very hard perimeters.

It’s also a lot more difficult for democracies, where a government can’t order welding of the doors of the population to ensure they don’t get out.

And possibly more importantly; without relevant immunity, these countries are still totally exposed. They will inevitably see the advent of spread again multiple times.

Minimise spread

There are a number of tools accessible to try to manage the spread.

Given that the virus predominantly spread through droplets, then mitigating the spread is mainly about avoiding the droplets to reach anyone.

Keeping distance to others will ensure no one can get hit by droplets. The debate here has been on an exact distance. That is as silly as an expiration date for food. This is not a binary but greyscale. The further away the safer. The probability is probably really low at one meter, and naturally even lower at two meters.

And if anyone with even the smallest symtoms stay home, then the contagious droplets can’t hit anyone.

Face masks? Well I think this is a good summary; Wearing one to protect others make sense, but staying at home when you are sick make a lot more sense. Wearing one to protect yourself is near pointless. You will still have pee on your pants and, assuming it even works at all, it will have virus on it so unless you handle it properly your will get it from the mask anyway.

The virus could also live for a period of time on surfaces from droplets spread. Getting it on your hands is not going to infect you, but if you touch your face, including eyes, there is suddenly a clear path into your body. For this reason, the recommendation is to clean your hands (properly!) and not touching your face.

Travel restrictions? Well minimising travel minimise the exposure, but this is only relevant if the spread is very different in the different areas. If you have the same sort of spread, then travel between them add no extra risk.

There could of course also be asymtomatic spread. This is relevant for all the scenarios where you need to identify all cases. But if your scenario is just aiming to flatten the curve, then this could be one of the small sources of spread that can happen without it being any problem.

Immunity

You can read, even on the WHO webpage that there is currently “no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection.”

Having said this, the Swedish autority says:
“It is unclear how long immunity against COVID-19 lasts after an infection. Based on previous experience, there is reason to believe that immunity will last long enough to prevent people from getting infected several times during the same season”. More was said in one of the recent press releases.

For all we know, it seems reasonable to assume that you will be immune long enough for a vaccine to be developed.

Vaccine

There is a general race to develop a vaccine. There is none at the moment.

There are two aspects here;

People are looking at if existing drugs might work. It seems some drugs can shorten the hospital stay, and there seem to be promising trials here.

But in general we need a vaccine that will cause immunity. You see statements that people expect to have one in a few weeks or months from now.

Please mind that establishing a substance that is a candidate is very much different that having a product on the market. The certification process is rather long (US example) to ensure that we don’t get new cases such as the Thalidomide scandal. Trying to save people, but ending up seriously harming millions is not the way forward.

Statistics

There are immensely much statistics available, and it seems common to just compare it. Swedish mortality is one popular figure from a Swedish perspective.

Number of cases – these are the number of found cases. We know that in most countries, only a fraction of the population is tested. So thinking the registered cases are the number of real cases is grossly misleading. The estimated number of unknown cases is the vast majority. This makes mortality and general spread computations very difficult.
Please mind that if you consistently measure the same way, you can still extract relevant information on trends and make very good estimated, even if the numbers themselves are not relevant.

Mortality – There seems to be very different ways to compute this. People die OF Covid-19 and people die WITH Covid-19. A patient with terminal cancer that gets the virus – what is then the CoD? Some countries don’t pick up metrics from long term stays for the elderly. And some countries don’t have compulsory centralised reporting. And also there is a general issue of day of death and day of reporting death. We see here a general lag, that deaths during weekends are reported only a few days later which makes graphs based on report date totally wrong. For people wanting to push forward a thesis, cherrypicking data has never been easier.