Covid-19 update… ‘coz you haven’t had enough of it already!

​What have we learned so far about Covid-19?

1. It spreads pretty well; each person infected and not isolated tends to infect another 2-3 people which can lead to an exponential growth in number of cases (currently over 80,000)
2. The incubation period is an average of about 5-6 days
3. The mortality outside of China is <1% (if you discount Iran which heavily skews the data with 15 deaths from only 95 cases)
4. If you put 3000 people in a closed environment with Covid-19 (Diamond Princess cruise ship) 695 people (23%) will get Covid-19
5. The World is putting a huge amount of effort into isolating areas with Covid-19 including Hubei province and yesterday Northern Italy

So how do we interpret what we have found out about Covid-19?

1. It spreads quickly and easily from person-to-person if we don’t employ the basic hygienic measure of strict hand hygiene, cough etiquette (use a tissue and wash your hands) and don’t mix with healthy people if you are unwell
2. The health impact of this infection on the majority of people is that it causes a mild infection a bit like the common cold or mild influenza; however if you are frail and already in poor health then the infection can be more severe (just as with influenza)
3. It is unlikely (and never was likely) that the measures taken by the global community will prevent the spread of Covid-19 around the World

 
What don’t we know about Covid-19?

1. The true mortality; at the beginning of an outbreak mortality data is skewed to severe cases with a higher mortality as only the sickest present to healthcare settings and get tested, the true mortality will be less than this
2. What is going on in countries with poor surveillance systems such as Sub-Saharan Africa; if Covid-19 gets into areas of the World with poor healthcare infrastructures with populations who are malnourished the mortality in those countries will be much higher than for us in the developed World
3. How many people are dying FROM Covid-19 and how many are dying WITH Covid-19; some of the people dying with a positive test result may be dying for another reason e.g. heart attack, cancer, etc. in which Covid-19 didn’t kill them but their death skews the mortality data
4. What is the impact of all of the resource being put towards controlling Covid-19 on other areas of healthcare; could people be coming to harm because of the distraction and redirection of resource?

 
So let’s have a look at some of what we know about Covid-19 and see if we can use this to explain some of the public health measures being employed at the moment.
 
The current management of the Covid-19 outbreak is based upon:

1. Reduced exposure to potentially infected people by restricting movement of people to or within outbreak areas
2. Rapid detection of new cases based upon broad definitions for potential cases
3. Isolation of new cases to prevent further spread
4. Self-isolation of exposed people so that if they become infected they don’t infect others
5. Quarantining of people with high-risk exposure until they are outside of the incubation period

 
All of this is designed to try and limit and slow down the spread of Covid-19. I suspect that trying to contain Covid-19 is like trying to turn back the tide, however slowing its spread does have a value.
 
Okay, so what happens if we slow the spread down?
Not only will this move any potential outbreak into the spring and summer when there is supposedly less strain on the NHS (yeh, really! Does the NHS actually experience a time where there is “less strain”). However in spring and summer people are less likely to be inside spreading their viruses around. The main benefit of slowing down the spread of the infection is that the overall peak of infection is less, so the impact at any one time is also less.
 
Consider 1) that everybody with Covid-19 might infect 3 other people and 2) they become unwell in 5 days. In my graph below (based on very crude and basic maths!) I have assumed that every infected patient infects 3 people who become symptomatic on day 5. These original patients and the new cases then infect 3 more people each, who again become symptomatic five days late (I’ve assumed at this 10 day mark the original patients are better). If we start with 100 patients and then follow this graph out to 1 month you can see that by this stage you will have over 400,000 infected patients to deal with!
 
What happens if we manage to reduce the number of new infections to 2 new patients per patient with a 5 day incubation period (by isolating and using PPE)? At 1 month this will reduce the number of cases to 73,000 patients. But if we manage to increase the incubation period to 7 days rather than 5 days (by delaying transmission by 2 days e.g. isolation and PPE), at 1 month we only have about 26,000 cases. These precautions slow Covid-19 down and this is why we have control measures in place at present.

Click for larger image

​In fact the number of people infected by a patient is known as the Reproductive Rate (RR). An RR of 2 means each infected person infects 2 other people, an RR of 15 means each infected person infects 15 other people. This number is important in outbreaks because if you can bring the RR below 1 then the outbreak is unable to sustain itself and burns out.
 
So this is the crux of all of the public health measures being taken globally. They are trying to get the Reproductive Rate to less than 1, so the outbreak burns out, whilst reducing the speed of spread so that the overall impact at any one time is minimised.
 
So if Covid-19 isn’t that bad why all the fuss?
Okay, some people are going to come to harm from Covid-19. The frail and the immunosuppressed and others with lots of comorbidities are at risk of serious infection with Covid-19. But that’s the case from all respiratory viruses such as influenza, Respiratory Syncytial Virus, Adenovirus, etc., etc. all of which we see as many thousands of cases every year. Therefore Covid-19 is going to cause infection in some people, and will probably replace the cause of their mortality from one of the more common viruses.
 
I think the main issue around Covid-19, and the main reason for the current public health strategies around the World, is to reduce the impact on the economies of affected countries. I know that sounds very cynical (and I am a cynic!) but even if it’s not the major reason it is a very real issue.
 
Think about it. If 20% of the population get Covid-19 and either are off work sick themselves, or having to be off work to look after sick children, then the economic impact of that missing workforce will be enormous. Factor in the number of healthcare workers not able to work because they have acquired the infection (including outside of work as well as from patients) then you can start to see the scale of the problem with people being unable to work.
 
Just look at what is happening to industries dependent on Chinese manufacturing which has ground to a halt in the worst hit areas of China. The same thing will happen in any country with sustained and uncontrolled transmission of Covid-19… at least until a large proportion of the population has had it and become immune, at which time transmission will start to go down, the RR will drop below 1, and the outbreak will burn itself out…
 
The other big problem PHE are going to have is repositioning the message from “killer deadly virus” to “it’s just like any other common cold” when Covid-19 is widespread in the community; I think the PHE might need a marketing agency to change this message for them.
 
At the moment there is a huge amount of amazing work being done to try and contain the virus, which currently involves: wearing hazmat suits, face masks, repatriating infected Nationals, testing an enormous amount of foreign travellers and self-isolating school children who have been on half-term skiing trips!
 
Once the government are no longer trying to contain Covid-19 (their 4-part plan is – Contain, Delay, Research and Mitigate) people will come into contact with Covid-19, and most of the patients will be related to cases who aren’t even known about (e.g. can you remember who you actually caught your last sore throat from?). When we get to thousands of cases, and widespread transmission in the community, this is when there will be no value in using PPE to prevent transmission in the healthcare setting, infection will be happening outside the hospital, just like flu does. The PHE message is likely to be one of “treat like any other respiratory virus and don’t worry about all of the space suits!” However this is going to be hard for everyone (medical staff, patients and the general public) to grasp. It is not because the danger from the disease has changed; it is that there is no longer a purpose in wearing the PPE. This is different to a viral haemorrhagic fever like Ebola, where the PPE is there to protect the healthcare staff from dying because Ebola has such a high mortality even in fit and healthy individuals. Covid-19 is not really the media’s “killer deadly virus”; Covid-19 is and will be as bad as many of the other respiratory viruses, which do have an associated mortality rate, especially in vulnerable patient groups.

Currently for Covid-19 the actions are all about contain it or slow it down, however watch this space as the advice will change if/when “containment” fails, then it will be cope as best we can with the influx of respiratory illnesses using all our “spare capacity!” :-)
 
… and then when this is over, we can all get back to our normal jobs… at least until the next big thing in the world of “woohoo it’s a new… virus, bacteria, parasite, fungus”.