COVID Q & A – Severity of Infection


Naturally Speaking’s blog series on COVID-19: scientifically-informed, data-driven answers to your burning questions about the coronavirus pandemic

Severity of Infection with COVID-19

This post comes in two flavours:

  1. Short and sweet – bite size summary
  2. Hungry for more? Look no further! This version includes a bit more detail and links to further resources.

If we don’t answer all your most pressing questions, please feel free to post them in the Comments section below – we’ll do our best to respond. We’ll also aim to provide any updates as advice and knowledge evolves.

Q. Why do some people respond better or worse to the virus than others? 

A. We don’t know yet. Clear risk factors include age, diabetes, high blood pressure, obesity, respiratory problems/ asthma, immunocompromised/HIV and other comorbidities, which are present more in the elderly. Men also seem to have more serious disease outcomes than women, with twice as many COVID-19-related deaths, although the reasons for this are not fully understood. It has been suggested that these differences might be due in part to overall health differences between men and women, and/or sex-related differences in immune response.

An excellent review paper (still in pre-print) recently summarized the characteristics of nearly 17,000 patients that presented with severe COVID-19 in the UK. The median age of those who presented to hospital with serious cases was 72, with the middle 50% of cases (interquartile range) aged between 57 and 82. The main comorbidities were cardiac disease (29%), diabetes (19%), non-asthmatic chronic pulmonary disease (19%), and asthma (14%). Just under half of the overall hospitalized cases included in the study (47%) had no known comorbidity. A higher proportion of cases were in men (60%), who also had higher levels of mortality.

An article in Science magazine nicely outlines the complexity of COVID-19 and the various ways it can affect the human body, impacting not only the respiratory system, but various other organ systems as well. The heart and kidneys appear to be particularly affected, with blood clots, vascular damage and/or kidney failure often contributing to disease severity.

SARS-CoV-2 enters host cells by binding to a particular enzyme, ACE2, while another enzyme, TMPRSS2, facilitates the fusion of the virus with the host cell. A recent study based on Italian patients suggests that levels of TMPRSS2 expression (how much of this protein the host produces) could be another risk for COVID-19 severity, although this needs further validation.

Q. What is the risk of COVID-19 for children and young adults? How important are they in spreading the virus?

A. Younger people are much less likely to become seriously ill or to die from COVID-19. However, children seem to be as likely to become infected as the rest of the population, with similar viral loads. Children could therefore be playing an important role in the transmission of the disease, although this requires further study. Given the current uncertainty around the role of children in COVID-19 virus transmission, it is difficult to evaluate what kind of impact school closures (and re-openings) might have on reducing virus spread, although it is currently believed that this is less important than other social distancing measures. It has been hypothesized that disease severity is linked to something called a cytokine storm – an excessive inflammatory response generated by the body’s immune system to try to get rid of the virus. The under-developed immune systems of children may be less likely to develop this type of immune response, consequently protecting them from some of the most harmful effects of the virus that ironically come from the body’s own ‘protective’ response.

Another factor that might contribute to differences in the severity of coronavirus-related disease across age groups is the interaction between COVID-19 virus and cold viruses, which are very closely related, and probably use the same receptors in the respiratory tract for entering the host. Since children are so often exposed to viruses that cause the common cold, this might interfere with COVID-19 transmission, resulting in a milder form of illness.

Q. There seem to be conflicting messages about asthma being a risk factor for COVID-19. What is the current evidence? 

A. Given that COVID-19 has been primarily thought of as a respiratory disease, it is perhaps surprising that asthma and other chronic respiratory diseases have so far not been among the most common comorbidities in reported cases. It seems that those with mild or moderate asthma are unlikely to be more at risk of becoming infected, or of having more severe disease. Consequently, simply having asthma does not necessarily mean that people should be ‘shielding’ (severely restricting their contact with other people to reduce their chances of becoming infected). The British Thoracic Society provides guidance on making this decision. Those with severe asthma, and particularly those on certain types of medication, are considered in the group at very high risk of severe illness from coronavirus. UK medical guidance encourages those with asthma to continue taking their medication, with the goal of keeping their asthma in check. 

Q. Is COVID-19 more or less severe than the SARS coronavirus? How does it compare with the flu virus?

A. COVID-19 seems to be more contagious, but with less severe symptoms than the 2003 SARS virus. The case fatality rate for SARS was estimated at around 15%. It is difficult to estimate the overall case fatality rate of COVID-19 because most of the less severe infections go unreported, and strategies for testing vary widely across the world. As testing increases, so too will the number of confirmed cases – including those that are less severe – which will lead to a decrease in the case fatality rate. The best available current estimate of the fatality rate for overall infected cases is about 1.4%.

Feature image is original artwork by PhD candidate Chiara Crestani, ©2020.

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