Viruses, Pandemics, and Immunity

Last year August, science writer Ed Yong put it very nicely in The Atlantic: "you see, the immune system is very complicated". Yet, understanding it is important to understanding how the COVID-19 pandemic might evolve, why we are faced with certain public health measures, and how we can hope to combat the pandemic with tests and vaccines. In this brief book, physics and chemistry professor Arup K. Chakraborty and immunologist Andrey S. Shaw offer a general introduction to how our immune system reacts to viruses, and how our medical inventions help out.

I was particularly looking forward to this book. Amidst the growing crop of books on COVID-19, the immunological details have been somewhat neglected. Kucharski's The Rules of Contagion looked at the epidemiology of disease outbreaks but was written just before the pandemic materialised (the paperback addresses this to some extent), while Rabadan's Understanding Coronavirus does what it says on the tin, focusing on the virus, SARS-CoV-2, and the disease, COVID-19.

Viruses, Pandemics, and Immunity is nicely balanced in the way it treats all the relevant elements to understand this topic. You get two chapters with history, introducing you to early procedures and to important scientists such as Edward Jenner, Robert Koch, and Louis Pasteur. By the end of it, you will understand the difference between variolation and the vaccine methods of respectively Jenner and Pasteur. This is followed by three chapters with the scientific nuts and bolts, looking at viruses, the immune system, and epidemiology, and two final chapters looking at the medical countermeasures of antiviral therapies and vaccines. In all of these chapters, details and findings on SARS-CoV-2 and COVID-19 are highlighted.

I admit that I found the middle three chapters a bit hit and miss. The one on viruses is, I think, great, explaining how viruses work by taking over the host cell's replication machinery, how DNA and RNA viruses differ, why COVID-19 went global while SARS and MERS – also caused by coronaviruses – did not, and how SARS-CoV-2 differs from other RNA viruses that we understand better, such as influenza and HIV.

In light of what I said earlier about the immune system, it is not surprising that the chapter on immunity is the longest. It introduces the two components of our immune system, innate and adaptive, and how both function when the body detects an intruder. The innate immune system is, relatively speaking, the simpler of the two, responding to infection immediately by recognizing general characteristics of bacteria, viruses, and fungi. The authors can describe this in five pages, including details on Toll-like receptors and cytokines. The adaptive immune system needs more time to gear up, 5-10 days in humans, and is the more complex of the two. In some 20 pages, the authors here introduce the byzantine arrangement of B lymphocytes that combat viruses directly, and T lymphocytes that destroy infected cells in the body, as well as the memory cells that both types contribute. But rather than discuss the innate and adaptive immune system in the order in which they get activated, the authors discuss them in reverse order, which I found a bit counterintuitive. Given the complicated nature of the beast, the level of detail might challenge readers not well-versed in biology, though a helpful "putting it all together" section runs you through it all again at the end of the chapter.

Similarly, the chapter on epidemiology explains the relevant concepts: the basic reproductive number R₀, epidemiological models, the effects of public health measures ("flattening the curve"), and herd immunity. The authors also highlight why different countries have been less or more successful in addressing the pandemic, something that will be explored in-depth in Fighting the First Wave. But here, too, the writing sometimes gets a bit complex. The authors spend three pages on a convoluted explanation with numerical examples to tell you that the more infectious a virus is, the higher the fraction of your population that needs to be immune before herd immunity kicks in. Furthermore, they exclusively discuss social distancing and different strategies to achieve herd immunity, from intermittent lockdowns to simply "weathering the storm". But the two other pillars of public health measures, hand washing and face masks, are not even mentioned, even though they make important contributions to reducing R₀.

The last two chapters are spot on again, focusing on the two main weapons in our medical arsenal. Antiviral therapies block one or more steps (entry, replication, assembly, and release) in the viral lifecycle and there is a brief discussion of existing antiviral therapies such as remdesivir and dexamethasone that have been repurposed for use against SARS-CoV-2. Vaccines, then, stimulate our immune system and this is where the immunological details come in again. The upcoming How to Make a Vaccine will cover all these topics in more detail, but there is a good introduction here to the different types of vaccines, clinical trials, and vaccine development, as well as the logistical challenges of the currently required large-scale production and a brief note on why vaccines are safe and certainly preferable over the alternative. Unavoidably, when discussing promising vaccine candidates against COVID-19, some information is already dated. The Moderna vaccine was undergoing trials when this book was written, while the AstraZeneca and Pfizer ones were in the developmental stages. All three are now being rolled out.

Throughout, the book is livened up with cartoony illustrations by Philip J. Stork, a senior scientist at Oregon Health & Science University. However, the decision to not include figure captions limits their utility in my opinion. Despite annotations in the figures, some are quite cryptic by themselves. Captions could have formed the perfect bridge and condensed the sometimes complex details found in the body of the text.

Viruses, Pandemics, and Immunity bundles introductions to a number of relevant topics, effectively replacing the need to e.g. get several Very Short Introductions. By highlighting what we know about COVID-19 and SARS-CoV-2 for each of these topics, this welcome book plugs a gap, especially where the immune system is concerned. General readers will want to heed Yong's warning though, because, you see, the immune system is very complicated.