As more information about SARS-CoV-2, the novel coronavirus that causes the disease COVID-19, is unveiled, researchers are gradually piecing together the larger puzzle of just how this virus evolves, spreads, and infects its hosts.
Most recent figures confirm more than 200,000 cases around the world, resulting in nearly 9,000 deaths. However, it is important to note that this number is changing by the hour. To understand what the research community does and doesn’t know about COVID-19, IFLScience spoke with Dr Ellen Foxman, Assistant Professor of the Department of Laboratory Medicine at Yale University School of Medicine. She notes that there is still much to be discovered about the virus and information is changing rapidly. She adds that a thorough review of known research is also available here.
IFLScience: Can you please outline the key stages of infection in people and how long each typically lasts?
Dr Foxman: We are still learning about this virus, but for the people who become ill, the time from exposure to the onset of symptoms is generally around five to seven days, but can range from zero to 24 days. The most common symptoms are fever and cough. Many people also report sore throat and muscle and joint aches. Over half of people develop shortness of breath. A large study of over 40 thousand cases in China reported that about 80 percent of cases had mild illness, 15 percent had severe illness, and 5 percent were critically ill. Hospitalized patients stayed in the hospital for 12 days on average.
However, we don’t have the full story on this yet. Early in the emergence of a new disease, the people who seek health care are usually the people who are the sickest, so most of the information that we have up to this point is from individuals with more serious illnesses. It is also possible that the virus causes mild illness or no symptoms at all in many more individuals, but we will not know this until there is more widespread testing for the virus throughout the community.
We don’t have too much data yet on virus shedding, but recent studies show that it is possible for the virus to be shed throughout the illness, and even after the patient recovers.
IFLS: What symptoms are similar to other respiratory illnesses like SARS, MERS, and influenza?
F: All of these viruses can cause fever, cough, and shortness of breath. All of these viruses can also cause severe breathing problems in some individuals, with SARS-CoV1 and MERS-CoV being the most likely to cause serious breathing problems and major illness. SARS-CoV1 and MERS-CoV are not currently circulating in the human population, so if you have these symptoms you are very unlikely to have SARS-CoV1(2003) or MERS. However, influenza and COVID19 viruses can have very similar symptoms and be difficult to distinguish without getting a test. A big difference is that for influenza, we have drugs for treatment and a preventative vaccine; however, we do not have these options quite yet for COVID19.
IFLS: What makes COVID-19 so novel?
This is a new virus for the human population, having recently crossed from animals into humans. This means that the human population does not have pre-existing immune defenses against this virus. Because of this, it is easier for the virus to spread from person to person and to cause illness.
IFLS: Even if someone is not experiencing symptoms, what should they do to mitigate the further spread of the virus?
F: The best thing to do is to limit contact with others, especially others who are vulnerable such as the elderly or those with pre-existing chronic health conditions.
IFLS: It appears that different age groups are impacted differently. Why is that?
F: That is a fascinating question. It appears that children can become infected, shed the virus, and even have evidence of lung infection on medical imaging, but still not experience very serious symptoms. This may be due to physiological differences in lung biology between children and adults, differences in the immune response between children and adults, or other factors we have yet to discover. On the other hand, the risk of having a serious illness goes up significantly with older age, with individuals over 60 being more susceptible to serious illness and people over 80 having the highest risk of severe illness and death.