Corona Virus and Basic Science

This post was prompted by my friend Craig, who wrote in a comment to a Facebook post:
"You know more about health care than the average person. Can you try to post 2x as much information (I just re-posted your WHO link) as outrage?"

He made a valid point in his comment. I happen to have a Ph. D. in biology, which included immunology and microbiology. I have been working in the biotech field ever since, and happen to have a certain affinity to math and statistics that perhaps is rare. Due to my background, some things are obvious to me that may not be intuitive to most people. Therefore, I'll try to share some of my understanding here. I'll use a "Questions and Answers" format that reflects on some of the common questions, statements, and misunderstandings.

Why is the Corona virus such a big deal, when so many more people die of other diseases?

This is indeed a valid question. The answer has several parts:

1. The corona virus (officially named SARS-CoV-2) is highly infective.
2. It is a new virus that is very different from others.
3. The corona virus is very dangerous to a subset of the population - in particular the elderly and people with pre-existing medical conditions.

Let's start with the highly infective part. Looking at clusters of early infections, it has been determined that every infected person infects, on average, about 2 to 4 other people. Those are just averages - there have been some cases where a single person has infected more than 20 others. But let's just look at the lower number of 2 new infections for now. The first person infects 2 others; these two infect 2 more each, for 4 new infections; those 4 infect 8 others; and so on and so forth. This is called an "exponential" growth. If it takes 10 days for a new sick person to infect others, let's see how the numbers develop over time:

Day	Infections
1	1
11	2
21	4
31	8
41	16
51	32
61	64
71	128
81	256
91	512
101	1,024
111	2,048
121	4,096
131	8,192
141	16,384
151	32,768
161	65,536
171	131,072
181	262,144
191	524,288
201	1,048,576
211	2,097,152
221	4,194,304
231	8,388,608
241	16,777,216
251	33,554,432
261	67,108,864
271	134,217,728
281	268,435,456
291	536,870,912

Within less than a year, this would result in more than 500 million cases! Now please note that the times given above are slower than what actually happened. The first case was reported in China on December 31, 2019, and the first cases in other countries about a couple of weeks later. 70 days later, the total number of confirmed cases had risen to more than 114 thousand cases (according to https://www.worldometers.info/coronavirus/). The actually observed number for each doubling of the number of confirmed cases is closer to 5 days in many countries.

Now let's look at why it matters that this is a new virus. This means that practically nobody has been exposed to the virus before the end of last year, so there is no immunity to it. Once the virus infects a person, it will multiply until the immune system mounts a response, which takes about 10-14 days. Until this happens, the infected person "sheds" the virus in large numbers, thereby infecting others.

For "older" common viruses like a cold virus or influenza, there is generally a substantial part of the population that has been exposed to the virus before, and still has some immunity to the virus. Think of the virus as a card counter walking into a casino: if he's been there before and is known, he'll be spotted and kicked out right away. If he's never been there, the casino will need some time to figure out what he does before they can kick him out.

So, what would happen to the numbers above if half of the population had been infected with it before, and still has a rapid immune response to it? Of the two people infected, one would "squash" the virus right away, and not infect others. So, every newly infected person would end up just infecting one other person, and the total number of new infections would never be higher than one.

The discussion above is somewhat simplified, since it ignores effects like mutations, "wear off" of immunity, and others. But the general principle it shows is correct: if a new infectious disease spreads exponentially, small numbers early on will balloon into very large numbers very quickly. To stop the spread of the disease, it is essential to drop the "average infection spread" rate to less than 1.

But the corona virus is not much worse than a cold for most people!

This is an argument that is quite often heard, and there is some truth to it. In the general population, about 4 out of 5 people who are infected will have symptoms that are comparable to the common cold. However, every 5th to 10th person will develop a more severe lung infection that can turn deadly. The infection is generally more severe the older the patient is, and also for patients with pre-existing health conditions. For some subgroups, more than 10% of the infected patients die, even with intensive care. That is substantially worse than for the common cold and even influenza.
The numbers are smaller for young, healthy people, but they are not zero.

But won't we have vaccines soon?

Unfortunately, there has been a lot of misinformation about vaccines against the corona virus. From a scientific perspective, the progress in understanding the virus has been absolutely amazing, and the same is true for efforts to develop a vaccine. It is quite possible that vaccine candidates will be developed in record time, perhaps less than 6 months. However, these will then need to be tested in clinical trials to prove that they are safe and effective. Such clinical trials typically take several years; according to experts, even highly accelerated trials cannot be completed in less than a year. Therefore, corona virus vaccines will not become available for at least a year, possibly two year - too late to stop the spread of the disease if it continuous at the current rate.
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I have to stop here for today. For additional information about the corona virus, please check the World Health Organization's website and the CDC website,

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This post was originally posted on 3/9/2020 at https://boardsurfr.blogspot.com/2020/03/corona-virus-and-basic-science.html