Virions are generally much smaller than bacteria (about 1/100th the size); due to their small size, virions can’t be observed with a microscope using light, but must be observed with a microscope using a beam of electrons, termed an electron microscope. When viewed under a transmission electron microscope, coronavirus virions appear with a “halo” akin to the halo of the Sun’s corona, which is visible to the naked eye during a total solar eclipse.

No, not “just like” them, though there are similarities. While symptoms of the flu can be similar to COVID-19, the flu is caused by influenza viruses, not a coronavirus. The Spanish flu of 1918 and Swine flu of 2009 were caused by H1N1, a strain of influenza virus(2).

Of the seven known strains of human coronavirus, four produce symptoms of the common cold, and three produce more severe symptoms. These three include the Middle East respiratory syndrome-related coronavirus (MERS-CoV), the Severe acute respiratory syndrome coronavirus (SARS-CoV), and Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 was also called the “novel coronavirus 2019” (2019-nCoV), and is the causative agent of the current pandemic. These strains differ in key ways.

(2)  Jilani, T.;  Jamil, R.; Siddiqui, A., H1N1 Influenza (Swine Flu). In StatPearls, 2020.

SARS-CoV-2 is the virus that causes the disease Coronavirus disease 19 (COVID-19).

While many infected with the virus may be asymptomatic or develop cold- or flu-like symptoms, other symptoms (upper respiratory, nausea, vomiting, and diarrhea) have been observed(3). A startling number of cases are more severe, and in some cases the disease progresses to pneumonia, respiratory failure, multi-organ failure, and death.

The case fatality rate depends on many factors, including gender, age, underlying health conditions, and availability of healthcare. While not all cases are diagnosed, resulting in a potentially overestimated fatality rate, reports of the symptomatic case fatality rate range from 0.8% to 3%, and age correlates strongly with increased risk(4).

(3)  Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19); World Health Organization (WHO): 16-24 February 2020.

(4) The Epidemiological Characteristics of an Outbreak of 2019 Novel Coronavirus Diseases (COVID-19) – China 2020. China CDC Weekly: 2020; Vol. 2, p 113-122.

I think of viruses as incredibly efficient tiny replicating machines. They are particularly efficient because a viral particle, or virion, packs only the essentials, namely genetic material inside a protective coating, as it journeys into a living cell and hijacks that host cell’s machinery for its own purposes.

Characteristics of viruses range broadly – viruses exhibit different shapes and sizes (“morphologies”), types and amounts of genetic material (e.g. DNA, RNA), and mode/timing of replication and release from the host cell. Systematic classification of viruses proves challenging due to this immense diversity, and they have been described as “organisms at the edge of life”(1).

This is a key way viruses differ. How many people will become infected given one infected person in a population of individuals susceptible to infection (so no vaccination campaigns or naturally immunity)?

This is known as the basic reproduction number and denoted by R0 (“R nought”)(5). This metric is a number, not a rate, and varies dramatically across diseases. The R0 is reported as a range, and for SARS-CoV-2 this value may range from 1.4 to 3.9. The lower the R0 the better the chance of reducing the spread and impact of the virus, and measures currently being taken across the globe are aimed at lowering the R0.

(5)  Milligan, G.; Barrett, A., Vaccinology: an essential guide. Wiley Blackwell: Chichester, West Sussex, 2015.