Coronavirus Variant Means We Have to Vaccinate Faster

F. Perry Wilson, MD, MSCE


January 13, 2021

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This transcript has been edited for clarity.

Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I'm Dr F. Perry Wilson from the Yale School of Medicine.

Well, it's 2021. We made it.

But forgive me if I say that it doesn't exactly feel like it. The challenges of 2020 have chased us right into the new year.

In the first week of 2021, 1.4 million new cases of COVID-19 were detected in the US. In that first week, 16,822 Americans died of coronavirus. That makes COVID-19, for now, the number-one killer of Americans in 2021, outpacing deaths from cardiovascular disease and cancer.


The best estimates, accounting for asymptomatic infections and variation in testing, suggest that 20% of the US has been infected with COVID-19. As the infection prevalence went from 0% to 20%, 375,000 Americans died.

If it weren't for the new vaccines, things would look pretty bleak. But the startlingly high efficacy rate of the Pfizer and Moderna vaccines, which started rolling out on the darkest days of the year, bring hope. The sun is rising earlier and setting later again.

But we have to face a new problem. And to drive home why it's such a big problem, I’m going to offer you a choice, in the style of a game we used to play in college.

Would you rather:

Have coronavirus mutate to be 50% more deadly or 50% more transmissible?

Assuming that you have the best interests of humanity at heart, you should actually go for the former. A more deadly coronavirus with the same transmissibility is better than a more transmissible coronavirus with the same deadliness. Of course, we got the bad version of "would you rather" with the B117 strain of coronavirus.

The math is nicely laid out by Adam Kucharski in a Twitter thread, but I'll recapitulate the idea here.

Okay. Let's say that we have 100 people with COVID-19, and each of them infects 1.5 other people. That's a fair estimate of the current transmissibility in a world where some — but not all — people wear masks. After 10 cycles of spread, we'd see around 5800 infections.


Let's say that the death rate is 0.5%, which is less than what we observe, but I recognize that we are missing some percentage of cases. So, after 10 cycles of infection, we have around 29 deaths.

What if the virus is 50% more lethal? Instead of 0.5% deaths, we go to 0.75% deaths. That's 43 deaths total.


Now what if the virus is no more deadly but 50% more transmissible? In other words, the average person transmits to 2.25 people instead of 1.5. Well, after 10 cycles of spread, we have a total of 332,525 infections. And at that 0.5% death rate, [1663] deaths.


This is why epidemiologists freak out so much about reducing transmission; increases in transmission cause exponential increases in deaths.

A more transmissible strain is bad. Like, really bad.

Intuitively, these more infectious strains are so bad because they spread faster. What can we do about it?

Well, we can vaccinate, and vaccinate quickly. So far, it looks like the Pfizer vaccine at least will be effective against this variant. There's no reason to think the Moderna vaccine won't work similarly.

And folks, we are doing a bad job of vaccinating.

At the time of this recording, around 22 million doses have been released to the states, but only 8 million (36%) have been administered. A New York Times article reported that 66% of New York City's vaccines are sitting unused, and some have even had to be tossed for spoilage.

This is unacceptable.

We need a massive mobilization effort to get shots into peoples' arms. Days, nights, weekends, vaccine fairs in parks, vaccine fairs in stadiums, vaccine drive-throughs. Shots need to come off the assembly line and go right into human bodies. Lean manufacturing, right? We need the funding-to-flow to do this. The presence of a strain with increased transmissibility makes this literally a race against time. And yes, we should feel okay giving a single dose without a clear plan for a booster; we need to reduce the susceptibility of the population at large quickly to avoid the high transmissibility of the new strain. Then we can play catch-up with boosters.

If we can come out with vaccination in a big way, we drop the transmissibility of the virus. A virus can't spread to a vaccinated person; they are the firewall. Mass vaccination is possible. The vaccines are there; we just need leadership — well, leadership and dollars — to get it done.

F. Perry Wilson, MD, MSCE, is an associate professor of medicine and director of Yale's Clinical and Translational Research Accelerator. His science communication work can be found in the Huffington Post, on NPR, and here on Medscape. He tweets @fperrywilson and hosts a repository of his communication work at

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