Updated on February 21th 2020, written by Dr David Owens.
We continue to get more data and information is evolving on a daily basis. I will continue to update this information in terms of:
The Disease: What will happen to me or my family if we catch this virus?
The Epidemic: How likely am I to catch this virus and is that risk changing?
The Director General of WHO gave an update on the analysis of the first 44,000 cases of COVID-19 in China. In this analysis 80% of cases cause mild disease, 14% severe disease and 5% critical disease. I have previously explained the difficulty of measuring mortality early in epidemics here. The mortality of this disease will ultimately depend upon the ratio of the number of severe cases to milder cases. We do not yet have an accurate and widely available test which allows us to distinguish the numbers in the population who died in hospital, were hospitalized with less severe illness or had mild illness and never went to hospital. It is my analysis that the evolving clusters outside of China (see below) suggest a larger number of milder cases and as explained previously, although counterintuitive, the more infectious this condition the less severe it is likely to be on a case by case basis. It is too early to be certain what the final case severity will be but for the reasons previously described, early mortality rates from previous epidemics are frequently downgraded with time. I think that is likely to be the case here.
Highest fatality rates are for people over 80 which is the same for all infections. There have so far been no fatalities in children and under 40 years of age the mortality is 0.2%. The high mortality in health care workers is likely to be explained by high viral load. Health care workers have always died in epidemics. They are working with the sickest people and we know that in many infections the amount of virus which an individual is exposed to is related to the severity of the disease that they suffer.
There is a significant increase in risk of males to females with highest risk in older males. Dr. Judith Mackay, a respected public health doctor suggested in a response to our initial article that this difference may be due to smoking. She points out that 50% of males in China smoke in comparison to 3% of females. We would certainly agree that part of the public health response should include advocacy for healthy living including exercise, healthy diet and not smoking. Further research will be needed to quantify these risks but it is another reminder than we must not take data from one cluster of disease and assume that it will always behave in the same way in different circumstances or different populations.
The current mortality in China after the change in reporting criteria is 2.9%. In the rest of the World excluding China it is currently 0.9% (11/1,237). These figures may increase if more of the currently ill people die. They may reduce if there are a lot of people who have mild infections.
An important recent study of 9 pregnant women suggested that the pregnant women in the later stages of pregnancy had a disease severity similar to non-pregnant women1. The infection did not transfer to their babies. Obviously, this will also be very important information.
The cruise ship and the international clusters including Hong Kong will give very interesting information about the infectivity and severity of COVID-19.
There are currently 69 cases in Hong Kong. The last CHP analysis revealed median age 59 years. 15 were imported cases and 37 possible or definite local cases. There were 13 individual clusters including the reported 11 out of 19 people who shared a hotpot meal. There is some spread within families. Importantly some of the confirmed cases have mild illness. The infected passenger on the cruise ship travelled between 20-25th January. Subsequently 634 passengers were infected. The first cluster of these people were infected between 26 and 31 days ago. Again it is important not to assume this cluster would be representative of different situations. Cruise ships tend to have older people with increased risk of other diseases. There are factors related to air quality, sanitation and central cooking facilities. There may be factors in this cluster which will later be shown to have facilitated spread. Regardless, the obvious infectivity in this situation in addition to the cluster involving 20 people in six countries which can be traced to a conference in Singapore2 between 20 and 22 January 2020 would support the suggestion that this illness, at least in some circumstances, is quite infectious in person to person contact and again would suggest a significant amount of unrecognized less severe illness in China which would again mean that the initial mortality figures on a case by case basis will have likely been exaggerated.
Although the virus can obviously be infectious in certain circumstances, so far, in 89% of cases of COVID-19 in which the individual had a travel history to China there has been no further transmission of the virus. This would suggest that most transmission occurs as people become more unwell and would generally be good news in terms of the potential for public health controls at least in the majority of circumstances.
There is no doubt that this is an important illness and some people will have severe complications. A notable feature of this illness is that some cases deteriorate and develop severe breathing difficulties. A disease with a low mortality can still cause significant impact if widespread. It can cause severe strain on health systems and this is the reason for the public health response.
As I have previously explained. Questions about the disease relates to the question what happens if something bad happens to me or my family? These are What If? questions. In order to understand the risk of this bad thing happening we need to replace these questions with What is the risk of catching COVID-19? To answer this question we need information. When we are dealing with uncertainties it helps to have an anchor for risk. In order to assess this risk we need to understand the epidemic.
I have given an update to my explanation of the epidemic here.
1. Chen, H., Guo, J., Wang, C., Luo, F., Yu, X., Li, P. J., et al. (2020). Clinical characteristics and intrauterine vertical ... Retrieved February 14 2020, from https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30360-3/fulltext
2. Coronavirus disease 2019 (COVID-19) Situation Report – 24. (2020, February 13). Retrieved from https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200213-sitrep-24-covid-19.pdf?sfvrsn=9a7406a4_4