Top 10 uncertainties about the coronavirus

PolitiFact has been fact-checking claims about the coronavirus and COVID-19 since it first appeared. Months later, we know much more about the virus and the disease than we did. But there are still confounding areas of uncertainty. 

Basic facts about the virus need to be hedged with caveats and warnings that our knowledge is limited or subject to change. Yet we need to strongly correct misleading and false claims, so sometimes the data limitations get lost in the discussion.

Here, then, is our list of the most pressing uncertainties to keep in mind as we go about our fact-checking work. 

Yes, there are counts of confirmed cases that the cable news channels feature regularly. But those are only reported cases. We don’t know the full extent of how many people have been exposed to the virus, formally known as SARS-CoV-2.

While some people are exposed, get COVID-19 (the disease caused by the virus) and end up in the hospital, other people get only mildly sick, and still others carry the virus without any symptoms at all. This means the true number of people who have the virus is larger than the number of reported cases, and probably much larger. 

If we don’t know precisely how many people have the virus, then we also don’t know where the people who have it are. Is the coronavirus mostly in big cities, or is it in the suburbs or rural areas? Are some geographic areas hit harder than others, or are they just testing less? We’ve talked to sources who have informed guesses, but nobody knows for sure. Also, the virus is on move, so whatever the picture would be today could be quite different in a few weeks.

The CDC says coronavirus spreads in droplets, which suggests you’d have to be near an infected person to catch it. But there’s nagging evidence that it spreads faster in enclosed spaces or where people work right next to each other (think of nursing homes or meatpacking plants), which suggests it has some potential to become aerosolized or airborne. Though rare, there are discouraging anecdotes of people practicing social distancing who get the virus anyway.

The coronavirus seems to be more contagious than the flu but less contagious than measles. Right now, researchers believe a person with the coronavirus typically spreads it to two or three others. (This is called the virus’s R0 or "R-naught" factor, and it’s 2 to 2.5.) But these are estimates, not hard data.

If someone is infected with the coronavirus, how likely is serious illness leading to death? This question is impossible to accurately answer. While COVID-19 deaths are being reported, we don’t have a full count of how many are infected due to testing limitations. Additionally, people who die at home of COVID-19 can be missed in official counts because they wouldn’t typically be tested after their deaths for the virus. So it’s impossible to know the true mortality rate. 

Here’s another layer of complexity: There are deaths per identified case, called "case fatality rates." Then, there are estimates from antibody tests and other models of deaths of everyone infected, called "infection fatality rates." (Scientists use models to predict flu deaths every year, but the coronavirus is too new and unstudied for that.)

Case fatality rates and infection fatality rates tend to be quite different, and scientists say both numbers have limitations. 

At first it seemed that children, for the most part, didn’t develop COVID-19 the way adults did, or that their symptoms were much milder. (It’s hypothesized that children can spread the virus, so schools were closed.) In recent days, medical authorities have warned that some children were experiencing a multisystem inflammatory syndrome, similar to Kawasaki disease, after exposure to the virus. But this syndrome still seems to be rare. How rare? We don’t know.

As for pets, the CDC says that there is no evidence they play a significant role in spreading the virus. But it does appear that the virus can spread from people to animals in some situations. But again, more studies are needed. 

When the pandemic started, the CDC described the basic symptoms of COVID-19 as cough, shortness of breath and fever. Since then, they’ve added chills, muscle pain, sore throat and loss of taste or smell, and they note that people may have a few symptoms but not all of them. Other less common symptoms have been reported as well, such as nausea, vomiting, or diarrhea.

Finally, there have been other anecdotal reports of people who’ve tested positive but have still other symptoms, such as swollen toes or mental confusion. As time goes by, the disease has shown that it can express itself in many different ways. 

Italy and New York City have been hit very hard with widespread infections and many cases of COVID-19. But other parts of the world haven’t. Why is that? Is it climate, or urban density, or older populations? There aren’t really clear-cut answers here. Recent reporting shows that people in Florida started socially distancing before state officials told them to, which also have contributed to lower numbers of infections. 

One of the infamous hallmarks of the flu pandemic of 1918 is that people thought it was over after it hit in spring, but then the flu came roaring back in the fall. Will the coronavirus behave the same way? The evidence points in different directions, and there’s no clear answer. There’s some evidence that the coronavirus transmits more easily in cooler temperatures with lower humidity, but a lot depends on how many people have already contracted the virus and which social distancing measures are being observed.  

If you get chickenpox once, it’s unlikely you’ll ever get it again, because getting it once confers long-term immunity. But obviously not all diseases work that way. You can catch the common cold over and over again, and to avoid the flu, doctors recommend a flu shot every year.

If you get COVID-19, it’s not clear if you can get it again or if you get immunity for a certain length of time. Public health officials say determining the answer will be important to ending social distancing. 

If people don’t become immune to the coronavirus after catching it, then it might be hard to create an effective vaccine. Right now, scientists are seeing preliminary evidence that an infection confers at least some immunity, but they don’t know how much. One of the biggest challenges for any vaccine is that it actually works; some vaccines never make it past clinical testing because they don’t actually give people immunity. 

Officials keep saying that a vaccine could be available sometime in 2021 — but that’s only if everything goes right. If researchers run into problems, for example with the vaccine’s efficacy or with side effects among patients, that timeline would get longer. The 12- to 18-month timeline is an optimistic assessment that might not pan out.