Where is this virus coming from and how did it manage to infect humans? Understanding this could help prevent events like SARS or COVID-19 outbreaks in the future. Also, it will help to understand the specific mechanisms of adaptation of zoonotic viruses.

When the pandemic was declared in March 2020, there were no vaccines or tested specific antiviral therapies for the SARS-CoV-2 virus with confirmed significant reductions in mortality. The medical community at the time was overwhelmed by the rapid increase in the number of cases and the escalating number of hospitalizations and deaths. Unproven ideas, sporadic case reports, and confusing information populated the news, social media, and even technical journals. For instance, hydroxychloroquine was considered by some a miracle drug, by some ineffective, and by others damaging. Political interests and wishful thinking polluted any dispassionate assessment. It was unclear at the time the pandemic was declared whether an effective vaccine or treatment would be available within a couple of years.

In the beginning of the COVID-19 pandemic, when people were trying to understand the severity of the disease, many comparisons were drawn between this disease and influenza. These comparisons have been a major cause of confusion and misinterpretation. Comparisons with seasonal flu, the influenza virus that comes every winter, led to the idea that the severity of the disease was similar, not taking into account that the virus that causes COVID-19 is new in the population, or that, unlike influenza, no vaccine or efficient antiviral treatment is known. The other comparison was with pandemic influenza, in particular the Spanish Influenza that caused tens of millions of deaths in 1918. The virus responsible for the 1918 pandemic was new in the population, expanded quickly, and caused a significant number of deaths in young adults. That was a time of global war, when influenza viruses were not even known to be the causative agent, and treatments were less developed.

Viruses are amazing creatures. They are the most common, the most diverse, and the fastest-evolving biological entities on Earth. They infect every form of life known, “hijacking” the complex machinery of cells and forcing them into submission. Being much smaller and less complex than cells, they have a unique, tiny kit of “tools” able to regulate the essential elements of cells and to “fool” their defense mechanisms. It should be noted that viruses do not exhibit any of the life properties we usually attribute to cells (such as metabolism, development, or sensitivity) other than reproduction. What viruses practically “do” is to enter cells, their “hosts,” and use the cellular machinery to produce new virus particles. It is not surprising that many important discoveries in biology during the last 100 years have been made from, and through, viruses. Viruses have provided fundamental clues to the principles of molecular biology, such as how cells replicate and handle their information and the mechanisms that cause cancers, among many others.

The COVID-19 coronaviruses is another type of flu. Coronaviruses and influenza are very different viruses. They do not share genes, proteins, or the same way of infecting cells. The disease that they cause is also different. Most infections of seasonal influenza are in the upper respiratory tract, while COVID-19 causes common lower respiratory tract infections as pneumonias that require hospitalization and intensive care for a fraction of patients.

When the first news of the outbreak of a new coronavirus that caused pneumonia in Wuhan appeared in January 2020, it was unclear what effect the virus would have on the population and economy of the world. Despite the repeated advice of health organizations, the containment measures came too late in many places. As cases and associated deaths crept up in different countries, the global concern changed to anxiety. This anxiety hovered between the uncertainty of bland denials and of grim predictions.

Once an outbreak starts, it is important to quantify how a disease is spreading, how it is affecting the population, and how different public health measures will have an impact on its effects. Epidemiology is the study of how a disease is distributed in a population, and of the different factors that determine this distribution. These studies can help to quantify the main population factors that led to the introduction and spread of an infectious disease in the population and the conditions that are associated with the severity of the disease. Epidemiology can also be used to assess the current extent of the disease and the effectiveness of different interventions, including different therapies and public health measures. Finally, it can also help to make predictions on likely future scenarios, given the current assessment of the situation and the different measures taken.

At the end of December 2019, an outbreak of pneumonia cases of unknown origin was reported in Wuhan, Hubei province, China. The patients presented with high fever and had difficulty breathing. Some, but not all, of these cases were in people who visited the Huanan Seafood Wholesale Market, where, in addition to seafood, a variety of live animals were also sold. Other infections occurred in people staying at a nearby hotel on December 23–27. All tests carried out by the Chinese Center for Disease Control and Prevention for known viruses and bacteria were negative, indicating the presence of a previously unreported agent. A new virus was isolated and its genome sequenced, revealing a similarity with SARS-like coronaviruses found in bats. Although very similar to the virus causing severe acute respiratory syndrome (SARS) in 2003, it was different enough to be considered a new human-infecting coronavirus. Clusters of infected families, together with transmission in medical settings, indicated that the virus had the ability to undergo human-to-human transmission. A month later, by the beginning of February 2020, the virus was found in several countries across the globe, and on March 11, 2020, the World Health Organization (WHO) declared it a global pandemic. The disease caused by the new coronavirus was called coronavirus disease 19, or COVID-19.

The virus infecting humans that is closest to SARS-CoV-2 is SARS-CoV, the agent that caused the SARS outbreak in 2002 and 2003. These two viruses are very similar in their genomes, in their way of entering cells, and in some of their clinical characteristics. Since 2003, we have learned many things from the virus that caused SARS. We have learned how the virus enters cells, how it replicates, and how it interacts with the immune system. We have learned some of the main factors that contribute to the worsening of the disease. Animal models have been established, and therapies have been developed and proposed. This acquired knowledge can accelerate the discovery of potential treatments for COVID-19.

Theodosius Dobzhansky’s essay, “Nothing in Biology Makes Sense Except in the Light of Evolution,” reflects on how evolution gives a powerful perspective to biological phenomena, able to integrate disparate pieces of information into coherent narratives. Biology can be messy, with many organisms, cell types, parts, and data. The recent revolution in genomic technology has generated a deluge of data that, correctly interpreted, can illuminate the relationship between and the ancestry of different organisms, the mechanisms that give rise to variability, and how this variability enables organisms to adapt to new environments.