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.

At the time of writing there are no vaccines or specific antiviral therapies for the SARS-CoV-2 virus with significant reductions in mortality. Lessons learned from the SARS outbreak have definitely helped us to understand many aspects of this emerging virus and the associated pathologies. But no effective therapies have been developed for SARS that could be leveraged for the COVID-19 outbreaks.

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.

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.

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. Most of these cases were related to 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.

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.

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.

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.