Everything you wanted to know about COVID-19 (Corona virus) but were afraid to ask
I was trying to pull my knowledge of Coronavirus matters together in one document for something and thought I’d post here too in case anyone might find it useful. I’ve abbreviated some concepts for easier understanding.
Summary
COVID-19 is an important illness. Most who will get infected will be quite unwell for several weeks but will recover. Unfortunately, some will become more severely ill and a small percentage will succumb to the effects of infection. Many groups are more vulnerable but there is a lot we can and must do to change the course of this infection for ourselves and the rest of our community.
Glossary
· COVID-19 this is the disease (COrona VIrus Disease discovered in 2019)
· SARS-CoV-2 (the name for the virus causing COVID-19 illness Sudden Acute Respiratory Syndrome Corona Virus 2, the first one was in 2002/03)
A good succinct visual summary of COVID-19 from the World Health Organisation can be found here
So what is COVID-19/Corona virus?
Corona viruses are a common group of viruses that infect a range of animals and humans. The “Corona” term reflects a corona-like structure when these viruses are visualised under a specialist electron microscope. Viruses are incredibly tiny and technically the simplest form of life, some would argue that they aren’t even alive but that is an academic point for another day.
At their most fundamental viruses are basically pieces of genetic message information designed to hijack cells to produce more of that message. Most viruses bind to very specific receptors (this point will become important later) on particular cells. Once bound they inject their genetic info into that cell and use clever programming to hijack the cell to make lots more of them. Uncontrolled, this hijacking could destroy the cell or the whole organism that the cell is found in. However, animal cells have several levels of tools with which to battle the impact of viruses. This battle between cells and viruses is at least a billion years old and it is estimated that up 1/20th of human genetic information is remnants of genetic info that came from viruses, a reflection of that battle over an unimaginable amount of time.
Because viruses need to bind to specific receptors they will usually only infect specific cells in a particular species of animal, at least initially. A few, rabies for example, can more easily jump from species to species but that is thankfully relatively rare and viruses usually only infect a narrow range of hosts. In some viruses, the means of storing the genetic information is relatively unstable and can change or mutate over time. Every now and again that mutation can allow a virus to “jump” from one species to infecting another.
Where did Corona virus illness come from?
Genetic analysis of the virus behind COVID-19, named SARS-CoV-2, shows strong similarities to other corona viruses found in bats and there is reasonably strong evidence that mutations in a bat Corona virus led to the current strain. It is also likely that it jumped to another species of animal before mutations allowed it to target humans. Claims that it was engineered in a lab are simply untrue. Similar mutational driven species jumps have caused serious corona virus outbreaks in humans, including SARS and MERS.
In humans the strains of Corona viruses (until now) infect cells of the throat and lungs and are responsible for about 1/3 cases of colds and similar illnesses. In healthy people these previous strains are highly contagious, annoying but usually self-limiting. Because this is a new virus in humans no one has immunity and everyone can potentially be infected.
How does Corona virus cause problems?
The SARS-CoV-2 virus binds to a specific part of lung cells called ACE2. This allows it to infect 2 important cell types in the lung. Cells that produce protective mucus and cells that have tiny hair like appendages on their surface called cilia. Both cilia and mucous are critically important for protecting the lung from damage and infection. Mucous captures dead cells, dirt and bugs that find their way into the lungs. The hairs of ciliated cells move in one direction, much like how the wind blows a field of ripe barley. That miniscule but constant movement moves mucous up against gravity and carries with it all the material that would otherwise lodge, damage and infect lung tissues out of our lungs and into our food pipe, where the actions of the stomach render it much safer.
This mucous cilia partnership is very important and conditions where it is damaged have very high rates of lung infection. For example, in the disease cystic fibrosis there is thickening of this mucous barrier and sufferers are at constant risk of chest infections. Cigarette smoke tends to paralyse the movement of cilia and hence smokers too have higher rates and greater severity of lung infections.
Our lungs have another way to get rid of dirt and infection- the cough. A coordinated movement of various chest muscles rapidly forces air out of the lung. In so doing, liquid mucous can be helped move upward.
How does the virus go from one person to another?
In parasitising key protective cells, the Corona virus is given unfettered access to more and more of the lung. The hijacked cells begin producing large amounts of new virus which mixes with the mucous bathing the lung. The whole of the breathing apparatus therefore becomes coated with billions of individual virus particles. The combined actions of cell damage and growing infection stimulate coughing as the lungs try to rid themselves of the burden. The action of coughing tends to move mucous upward but is so violent that it makes many small droplet particles consisting of mucous laden with new virus and in so doing the virus escapes its initial host (sneezing similarly produces virus-laden particles). So while an infected person breaths out they can emit a small number of virus particles (and hence there is a possibility of risk within a short radius), this is not thought to be an efficient way for others to get infected with this current virus. The virus also does not drift around more generally in the wind or the air. The main cause of infection is these droplets of mucous expelled at force. If someone is close by they can breathe in these droplets and the virus attack their ACE2 receptors in lung cells and start a new infection. The droplets can also survive on surfaces, including the skin of the hand, for at least several hours. Droplet are readily transferred from surfaces onto the hand, if the hand touches these surfaces (called fomites). If the hand comes near routes that avoid the skin barrier, including the mouth, nose or eyes, it can allow virus particles to the cause infection in that person. All prevention strategies are based on this understanding of how the virus spreads from person to person. Similar routes of transmission are seen with all other respiratory viruses, for example various flus and colds.
Our skin is an incredibly versatile and important barrier to the entry of various microbes viruses, bacteria and bugs. The Corona virus needs to get past that barrier if it is to pass on to a new host and form a new infection. In coughing/sneezing the emitted droplets are temporarily airborne. The droplets are proportionately heavy and tend to drop to ground within a short distance, a few of feet, depending on various conditions. If another person is within the immediate range of these droplets they risk breathing in these particles, giving direct access of the virus to a new host and establishing a new infection.
Because these droplets can deposit virus particles on a variety of surfaces (fomites) these surfaces can be a significant source of contamination. Equally if tissues are used, they can also become a significant source of infected material. Our hands regularly make contact with all types of commonly used surfaces around us. For example, doors, handles, chairs etc. most humans also have regular habits of touching parts of the face and the mouth. For example, perhaps up to 9/10 of us pick our noses (permitting both the transmission of virus out and access of virus into the nose and breathing tubes). Hands that have contacted droplets can therefore be a major route of transmitting viral particles across the skin barrier and causing new infection.
COVID-19 does not simply drift on the air. It does not arise out of thin air and can only directly travel a distance of a few feet. This means that my neighbour next door could be infectious and once we were a distance apart and did not share common contact with surfaces there would be no risk of my contracting the same infection.
What happens once the virus gets in?
Once some virus particles get in and bind to cells they can start to hijack the genetic machinery within those lung cells to make more copies of themselves. Some virus particles will get damaged or bind to other things, including mucous. So typically it will take a few virus particles to get to respiratory tract before and infection is ensured. Gradually, the cells produce more and more virus until they leak or burst massive amounts of virus. Other functions of these cells mostly stop. As virus leaks out of one cell, it will spread to more and more cells and a larger amount of lung cells will start making virus.
Lets look at this process from two different angles:
1) Initial effects on the infected person.
Initially only a small number of cells are infected and a newly infected person won’t notice anything. As more cells become damaged signals are released that suggest to the immune system that an invader is in residence and attacking the lung. These signals will be both physical and chemical. Physical signals will tend to make the person cough or sneeze more readily. The infection is usually deeper in the lungs and hence a runny nose is not a common symptom of this illness. The chemical signals in the blood trigger a number of non-specific and specific immune reactions. One of the early non-specific ones usually includes development of a fever. The raised temperature, chills and sweating are part of the immune response helping coordinate and optimise the reaction of the body. Often a person will usually feel tired and unwell as these non-specific symptoms begin to show. Specific specialist immune cells will also be recruited and start to migrate to the lungs and be stimulated to grow to produce sufficient cells and immune materials for the battle that is commencing there between the virus and the defences of the body. In the blood stream a wide range of antibodies will be produced until that one can be found which will bind to the virus.
2) External effects
In the early stages of infection, no symptoms will be evident and there won’t yet be enough virus being produced to be released from the lungs. As the amount of virus being made increases, it can increasingly be found in the upper part of the airway, the nose and mouth. This typically takes a few days and it is only at this stage that there will be enough virus for a special test to find virus. With this Corona virus, it does appear that some individuals can start producing enough virus to potentially infect another person after roughly 3 days. It is thought that while infections can be passed on at this pre-symptomatic state, it is the initiation of symptoms which acts as a great aid to the virus in spreading itself much more efficiently. Symptoms can be evident in some people 5 days after the first infection. For unknown reasons symptoms may take longer to appear in others but most (but not all) people will show symptoms within 14 days. 14 days is therefore typically used as the “quarantine period”. So if a person who might have been exposed to virus is kept away from others and monitored for 2 weeks and neither shows symptoms nor can virus be found in their nose by 14 days, they are regarded as non-infectious.
On average and roughly speaking one infected person will infect 2.5 other people during the course of their infection. There are roughly 5 days between one infection and it being passed to another. This number may sound small but means that if we start with one person on day 1 of a month, by the end of the month (30 days, 6 cycles of 5 days) 244 people will now be infected (2.5 x 2.5 x 2.5 x 2.5 x 2.5 x 2.5). So within a month 1 person infected will usually become 244 total cases, unless measures are implemented to stem the growth spread of infection. Uninhibited, by the end of the next month that number of cases will have become 60,000, all from one single case.
What does the infection do?
The typical symptoms of Coronavirus infection and the percentages of people displaying these is captured in the graph above. Almost all (9/10 people) will show a fever. The general symptoms are similar but not identical to colds or flu as compared below
Coronavirus can be distinguished from typical winter colds by its absence of a runny nose. Breathing difficulties are also much more common with Coronavirus than Flu.
Different individuals will react to the virus in a very large variety of ways.
All age groups can be infected and pass on infection but children almost always seem to bounce back quickly. The low symptom burden among children and young people can cause problems, since they may be carrying the infection for a time to vulnerable people (like grandparents) around them showing symptoms. Winter colds and sniffles are also still common among this age group at the minute so it can be hard to know what infections they may be carrying.
In adults, the immune response will become more specific and start to more selectively target the virus, and cells producing the virus. Virus shedding will peak and start to decline and the person will become less infectious until they can no longer infect another person and become immune to further infection.
Various different aspects of an individual’s immune system and background health will dictate what happens next. Many children have a relatively mild infection and their immune system curbs the virus until they recover. Some children do get sicker but among the tens of thousands of cases reported across all ages few children have died.
In some adults below the age of 50, their immune system will effectively curb the effects of the virus and they will have “mild” symptoms. Fever, tiredness, coughing etc. Although very unpleasant, most of these symptoms will resolve in 2–3 weeks. Most symptoms are seen in people 30–69 years of age. Mild cases can be effectively managed at home although these people will be quite sick, infectious and unavailable for work. Mild is still very unpleasant and very consequential for the person and those around them. It really means simply that they don’t usually need a long time in hospital or specialist care.
In a portion of adults, the physical effects of the virus will reduce the effectiveness of their lung defences against illness. Such individuals will develop a more severe illness and get an overt infection of their lungs, either by SARS-CoV-2 or by other opportunistic infections. This is called pneumonia. The infection will lead to shortness of breath, complete debilitation and is very frightening. Again in most young to middle aged adults, supportive care will see these symptoms resolve, although a person may be seriously unwell for a longer period of time. A high portion of these individual will need to be managed in a hospital environment but will recover after a few weeks.
Among an average, mixed age population, for every 100 people infected 80 of them will have mild or moderate disease. This means their disease was impactful, sometimes needing care in a hospital, but they recover. In the case of a further roughly 14 of those 100 people, the disease becomes severe, requiring significant supports in hospital. Among the remaining 6 or so people they will become critically ill and require major intervention to help keep them alive. These interventions can include being placed on a machine to make their lungs breath for them, taking their blood out of their body and putting oxygen in artificially. Their organs may begin to fail and they can die from these effects. Although the numbers differ from country to country (and are always better in health systems which have sufficient capacity to treat all patients), roughly 1–3 people per 100 succumb and die from their illness.
This is visualised in the graphic below from the WHO.
The burden of serious illness is not borne equally among all strata of those infected. Serious illness and death can occur among all age groups but are more common among those who are older and/or have other health conditions
The figure below shows the likelihood of dying among people of different age (orange) superimposed on the likelihood of people being infected by their age (blue).
Age is an independent risk factor because as we get older the function and reserve of all of the organs and systems in our bodies declines. This means that when challenged, it is more likely that the capacity of these systems to keep us well will be less and this gets to be a bigger issue, the older we are.
Impact of other already existing illnesses (Prexisting co-morbidities)
Analysis of the levels of deaths among people with different diseases shows that these illnesses can also play a role in the severity of the disease. Such data is complex to interpret because as people grow older they will tend to have underlying disease aswell, but there is no question that being older and/or being treated for specific conditions will increase the likelihood of much more serious consequences including dying. Older people and those with these conditions therefore need special protection.
How do people die from a corona virus infection?
In those who are susceptible, thankfully a minority, infection may result in a number of different potentially fatal effects on the body.
In some individuals, the damage and infection (pneumonia) in the lungs becomes so severe that they cannot put enough oxygen in their blood stream to support life. This infection can be from the virus itself and/or from other organisms growing and damaging lung tissue. The massive infection in such situations tends to deplete immune cells reducing the ability oif the body to defend against other illnesses and diseases.
In some people the growing level of virus infection triggers an amplified and cascading reaction among large parts of their immune system. This is called a cytokine cascade or cytokine storm and can become critical over minutes to hours. The cascade triggers a body wide malfunction of the immune system, disrupting and damaging most major organ systems which then began to fail. Death can occur due to multiorgan failure.
The parts of our body that control blood flow and pressure can be a target for the illness and in some people existing damage to blood vessels and blood flow can be amplified, causing signs such as blood clots. Again, organs may begin to fail as part of a large cascade of malfunction. The virus may also begin to spread more widely in the body.
In some individuals who initially present with pneumonia, they may initially appear to respond to treatment for a week but can then rapidly deteriorate as these other infection consequences begin to impact organ function. Hence, those in critical care will require major hospital interventions, are at high risk of death or may have permanent serious damage to organs, such as the liver or kidneys if they do survive.
On a side note, those in critical care will typically be shedding very large amounts of virus and pose a much greater threat of infection to healthcare workers looking after them. Hence specific extra protective equipment will be required as well as specialist isolation procedures.
Treatment and vaccines
Because this is a new virus there are no medicines proven to affect the course of the disease. Some experimental medicines already being examined for use in other serious viral illnesses may give a minor to moderate effect on the growth of the virus in people who are seriously ill, however, we will only know if this is the case when the results of clinical trials emerge in the next year.
Again because the virus is new there are no vaccines to immunise and protect people from infection. Corona virus uses RNA as the genetic information with which is propagates from one cell to another. RNA is less stable than DNA (which is used in all of our cells for this purpose) and hence has a higher rate of changes or mutations than DNA-based viruses. ThiS higher rate of mutation will make it more difficult to identify and develop a vaccine to protect against the disease into the future. Vaccines also take months to years to be shown to be safe and effective. Hence a vaccine will not be part of any large scale management strategy until at least 2022 and may not be technically possible at all. We still do not have a vaccine against the last corona virus outbreak, SARS, which occurred in 2002/03.
Transmission and its controls
As mentioned already, Corona virus is passed from one person to another on droplets containing individual virus particles. This is identical to other viruses that infect the lungs. While the information can seem daunting, this knowledge points to the Achilles heel of the illness. Preventing those droplets from getting from one person to another will stop the infection passing to other people. Although people can be infected from contact with people in the community (or the droplets they produce onto various surfaces), analysis from China indicates that much of the disease burden comes from the home environment, that is people who live under the one roof passing infection to one another. The WHO estimates that there is roughly a 1/10 chance that one person being infected in a household will pass on the infection to another person living there. Infection, even in the same household, is therefore not an inevitability, especially if control measures are used.
What are these control measures?
Since droplets carry the virus, preventing these droplets spreading to others is the most important thing that an individual can do. The measures sound simple but if everyone did them, we would have no Coronavirus and nor would Flu or Colds be spread either.
1) Catch the droplets before they leave. Many people sneeze or cough and spray out droplets, or if they try to catch it they use their hand. The former leads to an immediate mist of virus droplets around a person, the latter usually produces the same mist but also ensures that the surfaces of the hands, and any person or surface touched by those hands also becomes contaminated. While not fool proof, coughing into the crook of the elbow is more likely to catch larger droplets and is also not a surface that typically comes in contact with other surfaces. Sesame street showed us how to do this. https://www.youtube.com/watch?v=QW1yodZJpG8&feature=youtu.be
2) Use a disposable tissue. Again not fool proof but disposable tissues can help reduce the extent of spray. The tissues can then be safely disposed of in any bin where the droplets will dry and die off over hours and droplets on the hands removed and killed by washing.
3) Hand hygiene. Hand hygiene, washing hands, is the single most effective tool in reducing the burden of human infectious disease and is useful against a wide variety of diseases. Droplets of viruses can be invisible but easily be used to pass virus particles onto other people of to bypass the protective measures of the skin. This is because humans are tactile and use their hands for communicating, directly interacting with others, to fulfil nervous habits (eg finger in mouth, pursing lips etc), to rub irritations, eg itch eyes, and to remove deposits in the nose (9/10 of us regularly pick our noses). Again this sounds too simple to be true but the most common of soaps and warm water is amazingly effective at inactivating viral droplets. Alcohol-based handwashes are also effective, especially in situations where sinks and taps are not easily available. Regular handwashing is useful but when used tactically can be hugely effective. Many of us use public transport for example where there are many surfaces we must contact with our hands. However, tactical handwashing when we get to home or work can inactivate virus and ensure that these areas remain uncontaminated for ourselves and others.
4) Identification and isolation of those who are infected is a more complex but highly useful tool in curbing person to person transmission. In reality infected people are quite inefficient at passing infection to others. Think how many people you might meet over a 2 week period. By testing people and removing them temporarily from other contact, there is a major opportunity to break the transmission of virus between people. Testing has to be used with caution though because it only paints a picture of infection at the time of testing. There can be many many more people infected than testing shows. It can take time for an infection to show up through testing once it has been transmitted to a person, for example.
5) Social distancing and isolation can also have major impacts, again stopping the viral droplets from getting an opportunity to get to infect another person. Humans are a gregarious species though and vast swathes of our economy are ultimately dependent on bringing people together. So our travel industries, dining and entertainment all bring people closer together. Hence optimal strategies need to be employed that are effective but also cognisant of the impact of disruption on economics, political and mental health.
6) Extra measures for protecting the vulnerable. The various groups who are at elevated risk of serious consequences should they be infected have been outlined. More stringent adoption of these methods can specifically protect those people from infection from the rest of the community. Individual rigorously employing good etiquette and hygiene practices around those at greater risk can form an important shield against them acquiring infection.
Once established these measures can greatly control and curb the numbers infected and ill and greatly help the capacity of our various systems to manage illness and give highest likelihood of eventually overcoming the disease. This is illustrated by the visual below comparing ineffectual measures which allow near exponential spread from those where adequate measures are put in place and all of our systems can better control disease. This is the basis of the focus on “flattening the curve”.
The role of information and misinformation
Most people know very little about health and disease matters and when a new illness arises it can be frightening to the point of being paralysing We live in a modern information rich environment, with 24 hour news, various social media platforms and apps and easy global connectivity. It can therefore be hard to dissect out the details that we best need to keep ourselves healthy. In such times, it is vital that good quality information is readily and available and communicated effectively to people in a manner that they can understand and utilise it.
We can all play a part in doing this and adopting evidence-based approaches and thereby adjusting positive social norms that make our community better able to reduce transmission of illness.
Conversely, a media rich environment combined with fear allows for the ready propagation of material which can create undue panic or leave people vulnerable to financial or emotional exploitation. For example, false claims about treatments or cures can leave people out of pocket and operating under dangerous assumptions about how to protect themselves. Focus on materials that have little use, such as masks, may perversely expose those taken in by misinformation to elevated risk. We can all play our part by immunising ourselves against this misinformation and not passing it along to others in our social circle, therefore protecting them just as effectively as hand washing etc. False claims about breathing techniques or water sipping not only give a false sense of impacting the disease but can also greatly increase stress and anxiety when people continually receive them from people they trust. Wild rumours about neighbourhood infections, or shortages of essential goods in shops can generate wider panic essentially guaranteeing that these items won’t be available, especially for those who are older or infirm and may most be in need of those goods. Yes there may be disruptions, these are much more likely to be as a result of panic buying than supply chain issues. Careful preparation can ensure that we all in our community have what we need to keep all of our community supported. Corona virus is a public health problem and the solutions that protect all that we hold most dear, ourselves, our partners, our children and our older loved ones all rely on a public community approach.
Be nice!!
One final point, in times of stress it is easy to forget that everyone is stressed. Small kindnesses can be enormously more important than normal. At times like these we do well to realise how interdependent we all are on one another, locally, nationally and globally. Without the lady on the shop till, we have no access to soap or food. Without the delivery driver working hard, we won’t have basic goods either. The guy in the phone company, well he keeps us connected; and finally, doctors and nurses, we might be critically dependent on them to care for ourselves or a loved one. A smile, a thank you or a kind word helps keep life civil and worthwhile and just shows that no matter our creed, colour or ideology, we all value the part that each and everyone of us will play in getting through this.
Some useful resources.
In Ireland our public health authorities have generated a wealth of useful information resources and guides
These can be found here
https://www2.hse.ie/coronavirus/
More details for professionals here
https://www.hpsc.ie/a-z/respiratory/coronavirus/novelcoronavirus/guidance/
The WHO conducted a detailed analysis of the initial outbreak in china.Their invaluable report can be found here https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf
The CDC information pack can be found here https://www.cdc.gov/coronavirus/2019-ncov/index.html
The ECDC have a collection of resources and guides on their website https://www.ecdc.europa.eu/en/novel-coronavirus-china
Global and national cases can be viewed on an interactive tool here https://experience.arcgis.com/experience/685d0ace521648f8a5beeeee1b9125cd
