While you can see some patterns in COVID-19's victims (it is more likely to affect older people and people with chronic lung diseases, diabetes and weakened immune systems), there are a lot of stories that seemingly make no sense. So why do many healthy young people also get struck down by the virus? How does the virus choose its victims?
It all gets even more confusing, since according to recent scientific studies, only around 20% of infected develop any symptoms, while around 80% make a group of "silent spreaders". But what is the difference between people from those groups? The investigations on this topic are booming right now, so the information might be changing very frequently. To understand those patterns better, we need to know how the virus works and how it kills.
What happens with the person who is infected with COVID-19?
Coronavirus basic mechanism the same as for other viruses - it enters the cell and makes it replicate itself over and over. However, not every exposure means infection - the latter only occurs if the virus identified the cell as the one it needs to establish an infection. That causes direct damage and infection to the cells in the lungs, making people get fever and cough as well as some other symptoms. After that phase, some people get better, while others develop severe inflammation in their lungs which is likely a result of their immune system overreacting to the infection.
After the first encounter of the virus or the bacteria, the immune system begins to fight the invaders by releasing molecules called cytokines that function as signals for the cells that there is a problem. The stronger the immune response, the stronger is the chance to kill the infection, which is why usually children and young people are a lot less vulnerable to COVID-19. When the intruder is defeated, the immune system should shut off. Should, but it doesn't always do that.
In around 15% of cases of people battling a serious infection, the immune system keeps raging after the virus or bacteria are no longer a threat. The release of cytokines keeps going non-stop, making the body very exhausted while attacking healthy organs such as lungs or heart, which may eventually lead to death. This phenomenon is also known as cytokine storm. Those are known to affect people of any age, and certain cases from Italy and China exactly match the clinical outcomes of cytokine storm.
Since that overdrive normally occurs pretty rarely, there aren't many known treatments for it at this moment.
For the case of 42-year-old patient from Paris, doctors decided to try tocilizumab, a drug that is used to soothe an immune system in distress. After a few doses of the drug, the symptoms of fever disappeared and oxygen levels went back to normal, which indicates that tocilizumab might be an effective tool to fight the virus.
But, of course, that's only one of many interesting cases caused by the virus, and while some patterns are there, it still isn't known if it's just the immune system who is responsible for the lethality of the virus. The information we have right now is still not enough for us to learn the killing mechanism of the virus or the possible treatment for it.
What are the possible ways of treatment that are being tested right now?
The first method is the one described above - making sure that our immune system doesn't hurt us by muting the activity of interleukin-6 - a cytokine that is associated with an over-exuberant immune response.
The other idea is to use the classic method of treatment and preventing infectious diseases - passive antibody therapy. It involves the administration of antibodies against a given agent to a susceptible individual for the purpose of preventing or treating an infectious disease due to that agent.
In contrast, active vaccination requires the induction of an immune response that takes time to develop and varies depending on the vaccine recipient.
Thus, passive antibody administration is the only means of providing immediate immunity to susceptible persons. For passive antibody therapy to be effective, a sufficient amount of antibody must be administered. When given to a susceptible person, this antibody will circulate in the blood, reach tissues, and provide protection against infection. Depending on its amount and composition, the protection conferred by the transferred immunoglobulin can last from weeks to months.
The high amount of people who already recovered from the disease allows getting the antibodies relatively easily. Setting up the whole support system based on that method doesn't require any in-depth research and can be done in a decently short time.
A combination of that method and strict quarantine might lead to slowing down the infection rate if the passive antibody therapy will prove its effectiveness. However, recent discoveries show that there might be a problem with that.
According to scientists of Fudan University, after analyzing the blood samples of 175 patients from Shanghai, who recovered from COVID-19, it was discovered that around 1/3 of the group had an extremely low amount of antibodies, and 10 patients had no antibodies at all.
Researches also found an interesting pattern - the amount of antibodies gets higher with age. Recovered patients in the age group of 65-89 had 3 times more antibodies than the people from the 15-39 group. Around 30% of patients couldn't develop a high number of antibodies after the infection. This research indicates a much lower effectiveness of passive antibody therapy, but more samples from different places should be analyzed before making this conclusion.
The other strategy is to inhibit the replication of the virus in vitro using the drug ivermectin. According to the recent study of the Australian researchers, ivermectin can lower the amount of viral RNA in cells in 24 hours and delete it from the organism in around 2 days.
To test the antiviral activity of ivermectin towards SARS-CoV-2, Vero/hSLAM cells were infected with SARS-CoV-2 at an MOI of 0.1 for 2 hours, followed by the addition of 5 μM ivermectin. After 24 hours, there was a 93% reduction in viral RNA present in the supernatant of samples treated with ivermectin and after 48 hours the numbers reached 99.8%.
Normally ivermectin is used as a treatment for parasitic infections, but the drug has proved to be effective against a broad spread of RNA-viruses like HIV. However, it is important to understand that all tests were made in vitro, so further tests are needed to find the correct dosage for people and to realize the effectiveness of the drug.
The mechanism of how ivermectin interacts with viruses also requires additional research. It is likely, that it blocks viral proteins that allow the pathogen to infiltrate the cell, but it is unconfirmed.
It is important to say, that all of the methods above are still being tested and none of them are confirmed as being always useful or applicable.