SARS-CoV-2 Is Behaving Like a Textbook Virus

The constant drumbeat of ‘we do not know that yet’ is tiring

Credit: National Institute of Allergy and Infectious Diseases, NIH


We knew that this was a transmissible respiratory virus, yet when the virus began transmitting internationally, we said we weren’t sure if it would become global. Of course it would when, after a few weeks, it had already transmitted to many countries in Asia and the Middle East.


We know much about viral immunology. When antibodies started to be observed to wane, we said this is an otherworldly virus and thought we must learn everything about it anew. But that’s not so. It serves as a textbook example of immunity to an acute respiratory virus.

Testing and transmissible virus

We’ve seen major confusion about PCR, the role of Ct values, the limitations of PCR and antigen tests, and whether tests can help understand the infection status of people. Over and over, people say we don’t yet know enough to know about how to use Ct values to help determine transmissibility. But we do! We know so much and have known so much, i.e., we know that low Ct values mean someone is likely transmissible. We know that high Ct values are most likely to mean low viral loads.


This is the last point. I recognize we haven’t been with this virus for a full year and it’s not endemic, so it’s hard to know if it’s seasonal. But we know so much about it already from its closest neighbors. It was reasonable to make the leap many months ago that it is most likely seasonal — and we should have planned for it. Largely, we did not, and once again our policy leaders are being taken off guard as a major upswing in cases is precisely what we are now seeing.

Epidemiologist, Immunologist, Physician, Harvard Public Health/Medical School. Discuss vaccines, immunity, infectious diseases, public health,

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