An Epidemiologist Answers FAQs About COVID

Fall 2021 is here, which at the University of Michigan means that students are back on campus, the “Big House” is open for business, and I’m back in a classroom. My son is in school five days a week, I’ve flown on a plane, and am planning to host my family for Thanksgiving. And yet, in the US we have been averaging over 100,000 COVID cases a day for the past two months, and by the end of the day today another 2,000 or so Americans will die from COVID.

How can both these things be true? I’ll give you one guess: It rhymes with “Maureens.”

There are still some important questions out there and I wanted to take this opportunity to answer them (and thank the readers who sent them in). Here is FAQ Round No. 2. I'll address travel and booster shots in a later post.

Are you ordering more treats or pandemic doom-scrolling?

Source: Samson Katt/Pexels

Topic 1: Slowing community spread

Question 1. Do we have any way to quantify the reduction of spread (for Delta) that the vaccine provides? This is important in general, but this is also highly politically relevant because the vaccine mandate in the US is based on the idea of spread reduction.

First, a point of clarification: There is no single vaccine “mandate” in the US; there have been several mandates, and most are from either local governments (covering jobs like public school teachers, police officers, and others) or individual employers (like mine, at the University of Michigan, or hospital systems). That is, they are at the local level, not the state or federal level. The White House has issued a mandate for most federal workers, but even then these are people who work for the government.

Second, these mandates have not been instituted solely because vaccination reduces the spread of the virus: There are a lot of reasons why employers want their employees vaccinated that have nothing to do with reducing community transmission. For hospital systems, it ensures a healthy enough workforce to take care of patients (of all kinds: COVID, cancer, diabetes, and others). A contagious disease that keeps nurses, orderlies, cooks, janitors, doctors home sick for two weeks at a time is costly and it results in more burnout among those who are working, which in turn is associated with medical mistakes and poorer patient care. For hospitals to do their job of helping us get well, they need a workforce that has minimal chance of getting seriously ill. For universities where we have a large number of people living in congregate settings (that is, dorms), it is going to be really challenging to keep case counts low in that situation without mandates.

Third, to answer the question: The Delta variant is more transmissible than prior ones. It is transmissible even by those who are vaccinated, but that doesn’t mean vaccination isn’t reducing spread. Some studies have shown that people who are vaccinated have “high” viral loads for less time than people who are unvaccinated; they are contagious for a shorter period of time. And other research shows that people who are vaccinated have lower viral loads than people who aren’t, particularly when we include people who are asymptomatic (of which 40-60 percent of infections are thought to be). And if you are a glass-half-full type of person, there’s evidence from the Netherlands that vaccination reduces the likelihood that a person infected with the virus transmits it to another person from about one-third to one-tenth.

Question 2. With the current vaccination rate, wouldn't the US have a really high percentage of its population at close to full immunity? Because of that, shouldn't the current wave of COVID-19 be the last (without the rise of another strain)?

I think there is real, genuine evidence that this will be the last major wave of deaths and hospitalizations in the US (not of cases, which I’ll address below) because by Spring 2022, the majority of Americans will have some sort of immunity. That immunity is not perfect, and it is unlikely to be permanent (that is, people will likely need boosters, and the “natural immunity” of those who were infected previously will wane, just as it does for most infectious diseases). But that broad population immunity is going to save a lot of lives in the future. Hundreds of thousands of lives over the next few years in the US alone.

And we can get there faster with fuller uptake of vaccination (which, just as a reminder, not only reduces your personal, current risk of serious illness or death from this virus to nearly zero, because vaccination reduces the risk of infection (see Question 1), that means vaccination also reduces the risk that the virus mutates into something that evades our vaccines).

COVID cases will continue to circulate both in our nation and abroad because

• the vast majority of the world’s population does not have access to vaccines yet and likely won’t for several years, which means that the virus has plenty of opportunities to mutate (both here or in other countries)
• as those new variants emerge they cross borders and circulate, just as what happens with influenza each year

We will live with it, just like we do with other respiratory illnesses unless a more serious variant like COVID’s cousins SARS or MERS emerges, then we’ll be back to lock-downs.

Question 3. Why isn't anyone addressing the immune and their immunity?

If by “addressing” you mean “taking into account as part of our population immunity” the answer is researchers are addressing this: epidemiologic models that are used to predict case counts, waves, deaths, and more, build in both prior infections and vaccination. These are the models that inform recommendations from health departments about masks, mandates, and more.

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If by “addressing” you mean “letting people who have had a prior infection be exempt from their employers' vaccine mandates” (see Question 1): It is really hard to know exactly who has been infected previously (since a substantial number of cases were asymptomatic), and we know that there’s a lot more variation in the immunity that someone gets from being infected versus what they get from a double-dose of the vaccine.

Question 4. Why must everyone be vaccinated, including children under 5, and then not mandate it for the flu?

Because COVID isn’t the flu. Of every 10,000 people infected with the flu in a typical year, between one and five (0.01 to 0.05 percent) will die. Of every 10,000 people infected with COVID (pre-vaccine) between 100 to 200 will (~1 to 2 percent). Vaccination drops that number down to what we see with the flu. See here and here.

That’s a lot of lost human potential. A lot of grieving families.

Plus, we mandate vaccinations (actual mandates) for lots of infectious diseases—measles, mumps, and others. We’ve even eradicated diseases (like smallpox) with vaccine mandates.

Question 5. Why are we worried about the unvaccinated? The vaccinated and immune are supposed to be protected and the unvaccinated are taking their own lives into their own hands by choice, aren't they?

See 1 and 2 above. We care because unvaccinated people are prolonging the pandemic, dragging down the economy, burning out our already exhausted healthcare workforce, and risking not only their health but the health of their friends and families with negligible benefit to their well-being.

Listen: I hate being told what to do. This is part of why I like my job as a professor: I am my own boss. I know it is hard to put your trust in someone else (especially when that someone else is someone you don’t have any prior relationship with, like Fauci or the CDC or the FDA). But when it comes to most healthcare decisions we necessarily need to trust *someone.* Talk to a doctor you trust and ask them why they got the shot (if they are like 96 percent of doctors, they did). Needles are not fun, and I used to pass out whenever I got near one. *I get it.*

But there is nothing that would stop me from getting a vaccine if I didn’t already have one. In every aspect of life, there is no such thing as a free lunch, but every piece of data we have shows that if you have the opportunity to make a choice—which, thanks to a Herculean global effort and modern technology, you do—you should choose vaccination over “letting it ride” on getting sick.