Coronavirus: This is what we do and don’t know about Covid-19, explained by a virologist
University of Cambridge virologist Dr Jane Greatorex worked in Sierra Leone on the Ebola outbreak and for Public Health England during the swine flu epidemic.
Senior tutor, undergraduate and graduate tutor and director of studies in pre-clinical medical and veterinary sciences at Lucy Cavendish College, she was responsible for streamlining and improving HIV diagnostic services at Addenbrooke’s Hospital and maintains an active research interest in the influenza virus, most recently working on the shedding and survival of H1N1v, or swine ’flu.
Is it possible Covid-19 has been in the UK longer than we thought?
I understand where this idea is coming from because over the winter we did have some very long-lasting colds that a lot of people found very hard to shake off that also did combine with a cough. We had quite a lot of respiratory infections, full stop, over the winter. The answer is there’s a huge amount of genomics and sequencing gone into looking at where this virus came from.
There is no indication it came from humans so it would be quite remarkable for it to have been knocking around sooner than we thought. It is most related to animals found in Chinese markets, unfortunately. It can’t have arisen here.
Was it already here? No. Why would we then see it breaking out in China? The way it has spread would indicate that is where it has originated. We have had other infections over the winter that people may be confusing with it and the most persistent was a productive cough that people couldn’t shake, but that’s not the same thing.
Can you build up immunity to the virus?
We hope so, otherwise in China where you had massive numbers of cases it would have taken a lot longer for the drop in cases to start. You would have seen people in the most populated areas of the country keeping getting reinfected and that doesn’t seem to have happened. Modellers would have seen a difference if you were getting reinfection.
When will we know for sure?
To look at immunity takes a while. For example, with swine flu we didn’t really know how many people had been infected for nearly 12 months after the event because you have to give everyone’s immune systems time to respond and it takes weeks before you get that secondary response. What you are looking for in tests to check immunity is for antibodies. There’s an immediate immune response which says there’s a virus in your cells. From that innate response your body builds on that so that next time you meet the virus you should be immune but it could be a month down the line before you have a proper IGb (immunoglobulin) response.
If you imagine trying to chase up all those Chinese people who were infected – it is a really difficult thing to do. It will take a while to get enough data to show that people do mount a good response every single time. That’s what they would be looking for from everybody who is immunocompetent rather than those who are immunosuppressed, such as diabetics.
Can you relapse after recovering from the virus?
That doesn’t happen with these respiratory viruses. The symptoms that drag on are your body’s response to the virus but the virus is gone after a few days. I take great umbrage at the lengths of time you are meant to be infectious for because it is just not true. Nine days is nonsense. You don’t excrete a live virus that long.
Those studies are not checking for live virus, they are checking for genome. They do something called a PCR test (polymerase chain reaction), which is the test we are using to diagnose patients. It doesn’t tell you that you have live virus in your nose, it tells you have had it. For about 72 hours of a viral infection you have a live virus. In children it can last for longer – four or five days have been observed in flu.
So, there’s a big difference between how long we can detect the virus and how long they can infect someone else. With this coronavirus the only way you can say, yes, they are still shedding live virus, which is the only thing that will infect someone else, is if you take that sample from the patient and extract it and put it on tissue culture cells and then see it growing. That is done very rarely. There are not a lot of studies that look at live viruses. It is very easy to do PCR tests. It is harder to do live virus studies.
How long are people contagious before symptoms appear?
The likelihood is up to 48 hours before. The symptoms are your body’s response to the virus. This is what is called an acute virus, so its way of dodging your immune system is to get into the upper respiratory tract and get through the epithelial cells into your system and replicate like mad.
The way these viruses have evolved and the way your body responds is an acute inflammatory reaction so lots of histamine and something called cytokines are produced that ramp up your immune response. One of the first things to appear is that temperature because the virus is affecting a big area, your whole upper respiratory tract. You get a big cytokine response your temperature shoots up you feel horrible.
With this novel virus you get a dry cough form. That initial irritation and the cough is what the virus has evolved to produce. That cough is what sends the virus onto its next host. What we think of as the cold or the cough is actually your body’s response to the infection in the cells. These symptoms last much longer than the virus is live.
For whatever reason the common colds, which are also a type of coronavirus, don’t cause this same response.
Influenza always does. Influenza also causes pandemics because something about that virus causes a larger immune response.
If you get a persistent cough now, is it likely to be Covid-19?
I think it is becoming increasingly so. At this time of year we have passed the influenza A season. We are coming to the tail end of influenza B, so now it is most likely to be Covid-19. The virus has quite distinct symptoms, that dry cough, spiking temperature. It’s not like an ordinary cold.
Are pregnant women at risk of passing the virus to their baby?
As with all viral infections, when you are in your first trimester it could cause problems to an early foetus. However, there’s no evidence that during the later stages of pregnancy or during birth that you are going to infect the baby. I’m sure if you are coughing with coronavirus when the baby is born, they would separate you from the baby.
Why do children seem to be less affected?
We don’t really know why that is. There are a lot of unknowns at the moment. My worry over that issue is we are basing it on the Chinese and Italian data which are from populations that have a very high proportion of elderly people. Northern Italy and the whole of China have massively long-lived people so the data may be skewed.
We have to draw some conclusions because the Chinese data is massive but we have to be cautious of applying it to our own situation because we are a very different demographic here.
Is the data from China trustworthy?
Yes, there is very good data. The studies that have been done are excellent and so rapidly produced but it is all about the context in infectious diseases. There will be some genetic differences in the way that we respond to diseases. That’s not unheard of. So I have a bit of wariness. The data that is coming out of here matters the most and Public Health England is looking at that.
Will the government’s plans work?
Julia Gog is a mathematician in Cambridge who did a lot of studies post swine flu and then recently did one called Pandemic, which looked at people’s daily movements and the effects on the spread of the virus. They mathematically modelled all the data post-swine flu and looked at all the mitigations you could put in place like closing schools and stopping sports events and making people work from home.
All of them had relatively small effects. The one thing that seemed to have a massive effect was stopping travel and saying to people you must stay home. But that is the hardest one to bring in and it has massive other consequences. We have done so much work on this since swine flu. They are not the same but you can draw a lot of similarities looking at the best approach.
When you worked on swine flu did you consider having the army ring towns to stop travel?
It was modelled to see if it would be effective. But it's really hard to enforce in big places like London. It was talked about and thought about. You have to think about extremes like that because with swine flu, a flu epidemic the levels of death we were thinking about then were so huge and that virus spread very fast. It was in Scotland within two days of being discovered. I’m not working with the government now.
How long will the pandemic last?
There is quite good modelling on this, one model says it will peak around the end of April, which would be great - I think that is quite optimistic. Then one takes it as far as May. It will start dying off but its not going to die off in time globally to help the Olympics. It is helpful that most mass international sporting events are not going ahead with all the international travel.
Basing it on flu, which is the only thing we can compare it with, when we have had pandemics in the past there has been a bit of a peak around school time. It might tail off in July and August. And there might be a little peak in September when the little horrors come back. They are like virus factories!
There was a very good study on swine flu at Eton school, because it is a captive population. About 20 per cent of the boys there showed symptoms during a pandemic with a virus that wasn't meant to infect young people that much butand between 70 to 80 per cent were actually proven to be infected, which is fascinating because they all thought they were well. Whether those children would have been infectious, I don’t know.
More by this authorAlex Spencer