Welcome to another MedCram COVID-19 update. As we look at our Johns Hopkins coronavirus tracker, we can see where the infections are in the world. Recently they’ve updated this to actually show a little bit more in terms of location. So you can actually look and zoom in as you can see that the number of cases is starting to rise quite precipitously.
欢迎来到MedCram COVID-19的另一个更新。当我们查看Johns Hopkins冠状病毒追踪器时，我们可以看到世界上感染的地方。最近，他们对其进行了更新，以实际显示更多的位置信息。因此，您实际上可以进行查看和放大，因为您可以看到案例数量开始急剧增长。
I want to highlight this free app called the COVID-19 Tracker that was developed by a retired OBGYN physician in Florida and his team of developers at a company called Healthlinked. To look for additional trends and clusters of cases, they’ve created a platform for users to report if they have COVID-19-like symptoms and if they’ve been tested for it. As you can see this app has already become one of the most popular medical apps. As testing availability and challenges continue in the United States and other countries, apps like this could be a helpful tracking tool for hospitals and communities.
我想强调一下这个免费的应用程序，称为COVID-19 Tracker，该应用程序由佛罗里达州的一位退休的OBGYN医生及其在名为Health Linked的公司的开发人员团队开发。为了寻找其他趋势和病例群集，他们创建了一个平台供用户报告是否有类似COVID-19的症状以及是否已经接受过测试。如您所见，此应用程序已成为最受欢迎的医疗应用程序之一。随着测试可用性和挑战在美国和其他国家/地区持续存在，类似这样的应用程序可能成为医院和社区有用的跟踪工具。
It’s finally time to talk about immunity. This is a complicated topic, so we are going to go through it fairly slowly but at a rapid pace as you’ll see. You’ve got a cell. In this case, the cell has the ACE2 enzyme, which is the receptor for the virus. Here comes the virus, and on the virus are spike proteins, and it is these spike proteins that allow it to bind and come into the cell.
But inside this virion is an RNA molecule, and it’s this RNA molecule that gives instructions to the cell to make more viral particles. So what you get as a result of that are more viral particles.
Of course, each of those viral particles have their own RNA, which is copied from the original. But remember when that virus particle fuses with the cell, that membrane fuses with this membrane. Then the cell shows that it’s infected because it has those particles on the surface as well. So the general way that we’ve been testing for the virus is by looking at specifically the RNA, and that’s the testing that’s been done up to this point.
The technique that is used is called reverse transcriptase polymerase chain reaction or RTPCR. It takes a little fragment of that RNA, and it finds a specific sequence that’s unique to that sequence, and it copies it and then it takes that and it copies it, so it can amplify from RNA a bunch of DNA which looks just like it.
Because we have a certain code in that DNA that’s unique to that and therefore is unique to this RNA, we can put onto it a nice thing that lights up that will bind called a probe. If we see that this thing lights up, huh, we have a positive test. If on the other hand, we don’t see that, then the reverse transcriptase won’t recognize the specific sequence of that RNA, which is specific to this virus and no other, it won’t amplify it and we will get a negative result. This is how we test whether or not somebody is positive for COVID-19 or negative for COVID-19.
Unfortunately, based on the statistics that I have seen, notwithstanding some of the reports from South Korea versus their testing, I have seen anywhere from a 60 to 70 percent sensitivity, and some of you may see different numbers. Sensitivity tells you what percent likely that if somebody is negative, then you can rule it out. Though if someone test negative for coronavirus or negative for COVID-19, then there is, in this case, a 30% chance that they could still potentially have the disease. When you’re talking about isolating somebody, what you really want to have for sensitivity is something as close as possible to 99 or a 100% sensitivity.
So that’s been an issue with regard to this type of testing. Obviously this is the kind of testing that you want to do in the acute situation. If someone is infected with this coronavirus, and they have a bunch of these viral particles floating around, it’s going to be easy to detect whether or not they are positive. If the person has recovered, and there is no more RNA, then their test is going to be negative. If their test is negative, and here’s the key point: if the test is negative, there are two possibilities: number one, it could be a false negative or number two, they could have cleared the infection.
Here comes the issue with regards to reinfection, and that’s been the real key question up to this point. If you do serial testing on somebody, and you get something that looks like this positive, positive, positive, negative, negative, positive, positive, positive. Let’s say you tested them eight times in this situation. What is the reason why this is positive, is it because these were false negatives or is it because they truly were negative and then they got reinfected again? You don’t really know especially when you have a sensitivity that is less than a 100%.
Now generally speaking, when you do actually get immunity to the virus, what occurs at that point is antibodies are made to the virus, and specifically it’s going to be these proteins that are on the surface that are going to be the easiest to make antibodies. Antibody typically looks like this, it’s got a nice constant protein, and here are the variable ends, here with these being hypervariable where you can actually have different protein confirmations that will fit perfectly into this type of a spike protein.
So when you make these kinds of antibodies, the antibodies will signal out these types of cells and mark them for destruction by other parts of the immune system. In terms of a timeline, starting from zero here, generally speaking, what you would see the positive results at this point when you have the illness until finally you recover and the virus is no longer detectable, and that would be the reverse transcriptase PCR test, that’s this test over here. Then at some point, you’re going to develop an antibody response which is then going to be picked up. So these antibodies hopefully will give you immunity to this virus for the rest of your life. This is why you get vaccinations for measles, mumps, rubella, etc.
These are called immunoglobulins, but they’re different types of immunoglobulins, there are immunoglobulins that occur early in the immune response, and that’s called an IgM. So M is the first one that you would see and then later on, you’re going to get an IgG molecule instead. If somebody were to be positive on an IgG for a specific virus, then I would say you, generally speaking, had immunity from an infection a long time ago. But if your IgM was positive then I would say, ah, this is an antibody to a viral protein that must have happened just recently, maybe in the last few weeks or even days, depending on the immune response. Generally speaking, it’s more along the lines of weeks to a month or so.
What about testing for that? Well, the way that we test for these antibodies, scientists manufacture little portions of those spike proteins, but they are manufactured, and so if they mix their reagent with the blood from the patient which may or may not have antibodies, you’re going to see here that those antibodies are going to mix, and they will have a certain thing that occurs when these things mixed together, and it will turn out to be a positive test, and they can tell based on the test which we won’t get into, whether it’s an IgM or an IgG.
So this type of testing here on the right side of this line here is just now starting to come on. This could be potentially important because even though you might not have symptoms of the original infection, you will be able to know whether or not you have been infected using this kind of a test, and we will bring up other applications of this later on in this video. But understand that there is a difference between PCR testing and antibody testing. Antibody testing is checking to see whether or not you have immunity against the virus whereas the reverse transcriptase PCR is looking to see whether or not you actually have viral particles still inside your body.
So the question is in this situation, is the patient testing falsely negative because of these poor sensitivities on these reverse transcriptase PCR’s or is the patient really becoming infected again? There was a non-peer-reviewed article that recently put some of those questions to answer. This article set out trying to determine whether or not infection with the COVID-19 disease with the SARS-CoV-2 virus conferred immunity to the host for repeated infections afterwards. Now, let’s go over what they did, and I want to let you know that this does involve animal research, in this case, rhesus monkeys, which are fairly close to us in terms of genetics.
They took four rhesus monkeys, and they infected all four of them with the SARS-CoV-2 virus. All of them had similar symptoms, the symptoms and signs that you would imagine. They lost a little bit of weight, they showed signs and symptoms of the virus. Furthermore, they checked viral loads using that reverse transcriptase PCR that we talked about, and those peaked at about three days in all of the monkeys.
Of note, they check not only the nasopharyngeal swabs, but they also did anal swabs to make sure that they had checked for viral shedding in both places, and the peak was around three days after the initial infection. They sacrificed one of the animals, and after evaluating the monkey they went to go look to see exactly where the virus ended up in that body. They were able to see that the virus was in the nose, pharynx, which is the mouth, lungs, which is where most of the virus hung out, the gut, spinal cord, the heart, skeletal muscle and the bladder.
Then what they did in the remaining three monkeys is they measured antibodies at day 14, at day 21 and at day 28, and what they saw in those three remaining monkeys were all of the things that you would notice to see if someone had immunity, which was basically there were increasing signs of antibodies being made, showing that these monkeys were recovering from the initial infection of the SARS-CoV-2 virus.
Of note, they looked at the chest x-rays on day 28, and the chest x-rays were negative. They were essentially normal at that point. The other thing that they did was check the viral load at that time as well using reverse transcriptase PCR, and in all of them, the viral load was all negative. So at day 28, we essentially have recovered primates without an abnormal chest x-ray and with undetectable viral load.
What they did on day 28 was they reinfected the remaining three monkeys and monitored them. Other than an initial spike in temperature in all three of them, they showed none of the signs that they had back here with the weight loss and the signs and symptoms that you would expect with a viral infection. None of those signs were present other than a very small spike in body temperature which quickly went away.
And after about five days they sacrificed one of these animals and looked to see if there was any kind of abnormality or virus anywhere, and they looked in all three of these a total of 96 times to see if there was any virus, any viral load using RT-PCR, and the answer in every single case was none.
When they looked at that sacrifice monkey after five days, they showed that there was no viral replication in all tissues, as well as no pathological damage and viral antigen in lung tissues. They go on to say, ‘’therefore our results suggested that the monkeys with SARS-CoV-2 infection after recovery could not be reinfected with the same strain. Longitudinally, the monkey that had undergone single infection in this study did not appear to show signs of recurrence after the recovery, either’’.
Taken together the team concludes: ‘’our results indicated that the primary SARS-CoV-2 infection could protect from subsequent exposures which have vital implications for vaccine design and disease prognosis’’. That is not to say that it would be unusual to have multiple infections of the same virus. This was documented several times in his reports on the epidemic of smallpox in Trinidad from 1902 to 1904.
On page 83, Dr. Seheult talks about second attacks, the possibility of second attacks was recognized as far back as the 10th Century by Rhazes, the Arabian Galen, and his experience has been confirmed by many observers up to the present day. He goes through and actually documents in several patients that he attended to in Trinidad on people who had multiple bouts of smallpox, even some that had been vaccinated successfully. And who is the author? Dr. Murray Francois Raoul Seheult who happens to be my great grand uncle. He was the top surgeon in the colonial hospital in Port of Spain, Trinidad.
在第83页上，Seheult博士谈到了第二次袭击，Rhazes，Arabian Galen早在10世纪就认识到第二次袭击的可能性，直到今天，他的经验已得到许多观察家的证实。他仔细检查并实际记录了他在特立尼达（Trinidad）接受过治疗的几例患者，这些患者患有多发性天花，甚至有些人已经成功接种了天花。谁是作者？穆雷·弗朗索瓦·拉乌尔·塞休特, 特立尼达西班牙港殖民医院的高级外科医师, 也是我曾祖父的兄弟。
Despite this though reinfection is a rare thing. In this case, in the SARS-CoV-2 situation it seems as though the virus follows what we normally would see, which is if there isn’t that much of a change in the virus, hosts develop immunity to it.
So if that’s the case, can we have blood tests quickly that would check for antibodies? It could be very helpful if we could check for antibodies because we could see who was actually infected, how widespread is the infection. If it is widespread enough, you might be able to actually at 50, 60 even 70 percent get into herd immunity where the virus would not spread as fast, and you would not have to do isolation.
In addition to that, you wouldn’t have to worry about personal protective equipment in healthcare providers who already have antibodies because they wouldn’t be able to get the disease again.
Here’s an article that was published in Science that looks for new blood tests. They basically go over the same things that we’ve been talking about, companies have been racing to develop antibody tests.
Here’s one out of Icahn School of Medicine at Mount Sinai. They posted a preprint yesterday describing a SARS-CoV-2 antibody test that they’ve developed. It’s a relatively simple procedure and other labs could easily scale it up. Then they go on to describe exactly what we’ve talked about, where they find that this spike protein on the outer coat to see whether or not it will bind to antibodies if they’re there, and if they do bind to these receptor-binding-domains as we talked about, then it would trigger a detection so that you could see whether or not the antibodies are there.
Here’s another antibody test, BioMedomics, who is still seeking FDA approval on this COVID-19 rapid diagnostic test. You can see here that it’s fairly simple. We’ll put a link into the description below regarding this, but in terms of the sensitivity and specificity, let’s take a look at that.
This was published in the Journal of Medical Virology, the Development and Clinical Application of a Rapid IgM. Remember we talked about IgM being in the acute phase and IgG being in the more chronic phase, combined antibody test for SARS-CoV-2 infection diagnosis. The overall testing sensitivity was 88.66%, meaning that if you had a negative test you could be 88.66% sure that that was not a false negative result.
Additionally, specificity was 90.63%; that means that if the test was positive there is a 90.63% chance of it being a true positive. Again, high sensitivity means that if it is negative, you can rule out; high specificity means that if it is positive you can rule in. In both cases here, we’ve got good results.
So we hope that this test gets FDA approved soon so that we are able to do antibody testing to see who has had the disease already, and who may not have known it. That’ll give us an idea about herd immunity and how fast this virus is going to continue to spread. Remember that if 50 to 60 percent of the people in a community already have tested positive for the virus, it is very difficult for that virus to spread much more. Also, healthcare workers can be tested, and if they’re positive and have already had the disease, that could potentially save equipment for those that have not yet tested positive.
While we went over a lot of things today, I would offer you a couple of reminders for those health care providers that want a refresher course or to learn it for the first time, don’t forget our free course on updating and learning about ventilator management.
I hope to over the next number of days this week go over practical things that we can do to improve our immunity as this virus continues to spread throughout our community.
Thanks for joining us.