A lot of our early assumptions about the new coronavirus have flip-flopped.

This is normal. That’s how science works — it’s a process of being less and less wrong over time. COVID-19 is new, so there’s lots of uncertainty. And the pandemic’s size and scale caught us by surprise. As we learn more, our understanding of the virus continues to change.

Here’s what we now know:

Masks are useful after all

Were you dubious about the U.S. Centers for Disease Control’s early assertion that mask “leakage” meant that it wouldn’t protect you from a virus? Join the crowd.

The CDC has since reversed its position. And an influential study in the Annals of Internal Medicine — which concluded that masks do not effectively stop virus-laden droplets — was retracted due to statistical problems.

Now we wear them everywhere — indeed, they’re often required. While masks don’t offer perfect protection, any kind of impediment is better than nothing. And if you’re sick, a mask can help keep you from spreading the virus to others.

Don’t just blame China; our early cases came from all over

To be sure, the crisis first emerged in the central Chinese city of Wuhan. So that’s where U.S. authorities focused their attention. In fact, the only way you could get a test was if you had recently traveled there, or had contact with someone known to be infected.

A new UC San Francisco genetic analysis reveals that California’s viral lineages are as diverse as we are. While some early infections can be traced to China, several others arrived here from Europe. Domestic travel was also to blame: Of the 20 first travel-related cases at UCSF, 14 were linked to travel within the U.S., including six from New York.

It’s less deadly than we first feared

Early on, death rates varied widely by geography — but they were all scary, ranging from 2% in South Korea, 4.3% in the U.S. and 13% in Italy. While we assumed the risk would drop as testing expanded and infected people recovered, we didn’t have reliable numbers.

With more data emerging, the CDC has revised the estimate downward. The current U.S. death rate for those showing symptoms ranges from 0.2% to 1%, with a “best estimate” of 0.4%. That’s still much higher than the seasonal flu’s 0.1% death rate — but it’s better than we feared. Still, until there is a vaccine, we are all vulnerable. And the death rates for some people, such as elders and those with other illnesses, remain extraordinarily high.

It’s spreading more slowly

Initial estimates suggested that each person with the virus could infect two to four people — a rate that would quickly accelerate an outbreak, if nothing is done to reduce it. A subsequent study from Los Alamos National Laboratory placed it even higher: 5.7.

Experts now calculate that the nation’s current transmission rate ranges from .90 to .95. That’s great news: A value under 1 signals fewer new cases in an area, whereas a value of over 1 means more cases.

What’s changed is our behavior, not the virus. Tough restrictions, such as stay-at-home orders, reduced infections. And if we let down our guard, it could pop back up again. Already, there are hints that reopening and relaxed behaviors are contributing to transmission rates over 1.1 in Utah and South Carolina.

It’s not just a respiratory disease

Many early symptoms seemed to involve the lungs. Patients had pneumonia, coughed and couldn’t breathe.

Now we know that the virus can attack other parts of the body. In April, the CDC added new symptoms, such as sore throat, muscle aches and fever. Gastrointestinal problems, such as diarrhea and nausea, have also been reported. Some people complain of loss of smell and taste and neurological symptoms, like dizziness. An infection can even cause mysterious and painful lesions on the toes, weeks after acute illness.

And, disturbingly, a growing body of evidence suggests that patients are suffering from strokes as a result of blood clots.

Your mail probably won’t kill you

Remember wiping down every letter, package and groceries? It made sense, at the time. We were anxious about lab studies showing the virus could live hours, even days, on surfaces.

Now, with months of experience under our belt, we know that it’s close contact with others — often during gatherings of friends, family or co-workers — that is driving the spread of the virus. Experts say the highest risk of infection is in enclosed, crowded and connected environments, such as households, meatpacking plants, prisons, churches and nursing homes.

Your bag of lettuce is not a main driver of the epidemic. Or that letter from Aunt Nancy.

Children aren’t completely safe

In those dark days of the pandemic, there was this silver lining: Not a single California child died. While kids make up 22.5% of the population, they’re only 5.7% of COVID-19 cases. And their illnesses are milder.

But the emergence of a rare complication shows that youth are not completely spared. The CDC reports that a serious inflammatory reaction — called “multisystem inflammatory syndrome in children” (MIS-C) — causes rashes, a persistent fever, abdominal pain and diarrhea. There have even been cases of heart failure.

You were smart to store toilet paper

The panic-stricken rush on toilet paper was one of the most bewildering moments of February and March. We were scolded for being hoarders, accused of fear and greed. After all, COVID-19 isn’t a diarrheal disease. How much toilet paper does any one family really need?

Here’s what we’ve come to appreciate: It kept us home. When infections were skyrocketing, we weren’t wandering the aisles of CVS or Costco.

And because we’re home, we need more of it. With an estimated three-quarters of the U.S. population under stay-at-home orders, we’re not visiting the commode at work, school, restaurants or coffee shops. Toilet paper manufacturer Georgia-Pacific calculates that home usage is up 40%. To last just two weeks, a four-person household would need 17 double rolls.


In a short six months, we’ve learned a lot about a once-mysterious pathogen and pandemic.

But much else remains maddeningly unclear — so many of today’s certainties will be tomorrow’s corrections.