There is a growing body of evidence that the SARS-CoV-2 virus that causes COVID-19 is spreading. Here’s a rundown of what we know:
A relatively low number of cases of COVID-19 have been reported in the U.S. (128 cases according to the CDC as of March 4). This does not mean that screening and quarantine measures were effective nor that the virus has miraculously spared Americans. What it means is that we haven’t had the capacity to test everyone who could have it.
Problems with an early version of the test led the CDC to restrict testing to only patients with the most severe illness and likelihood of infection. In other words, only a fraction of the sickest patients have been identified. As the U.S. ramps up testing, the numbers of cases will grow, likely by a lot. I wouldn’t be surprised to see massive spikes in case counts in the coming week(s). It’s important to remember that this doesn’t mean that infections escalated overnight, just our ability to identify them did.
New cases of COVID-19 that aren’t traced to exposure provide evidence that SARS-CoV-2 is present in the community and can cause mild disease or perhaps no disease at all (also known as asymptomatic infection). This is notable because mild illness typically doesn’t prompt medical attention and can be missed, but people with mild symptoms can still contribute to the spread of disease. It is hotly debated whether asymptomatic people can spread SARS-CoV-2. If true, this changes the dynamic of spread considerably since it would be impossible to know who are serving as COVID (Typhoid) Marys around us.
Another piece of evidence that SARS-CoV-2 can cause asymptomatic or mild disease is from genetic sequencing of the virus from two patients in Washington state. The similarity in sequences between the virus isolated from the very first travel-related case in the U.S. on January 20 and another patient over six weeks later suggest that the second patient’s virus was descended from the first. But the timing of their infections indicates that the virus was probably circulating in the community for weeks in between. That is, patient #1 did not directly infect patient #2. Instead patient #1 infected someone else who probably had a mild illness that went unnoticed, who then infected another person who had a mild illness, and so-on-and-so-forth until patient #2 was identified. Hundreds of people are estimated to have been infected between these two patients.
The first studies describing characteristics of patients with COVID-19 only included hospitalized (ie. very sick) patients, so the extent of mild or asymptomatic infection wasn’t clear. Last week, the largest cohort study including over 40,000 of the earliest patients with confirmed COVID-19 in China was published in the Chinese CDC Weekly. In this study about 80% of patients had mild disease, which was defined as non-pneumonia or mild pneumonia (the extent of symptoms in these patients wasn’t reported). In the absence of mass screenings, we don’t really know how many patients have infection with only very mild symptoms or no symptoms at all.
Notably, children seem to be spared from COVID-19. Kids and adolescents under 20 years old made up about 2% of all cases and only 0.2% of all deaths in the cohort study described above, with zero deaths in the 0-9 year old age group. That’s not to say that children don’t contribute to the outbreak–they are notorious germ spreaders to-be-sure, but they seem less inclined to severe disease, which is certainly a relief to parents.
Because SARS-CoV-2 is a novel human pathogen, we are all susceptible to infection until we are exposed or immunized, whichever happens first. Given the current estimates of infectivity and reproductive rate of the virus, this means that it’s possible that SARS-CoV-2 may infect many of us before a vaccine is available. Marc Lipsitch, an epidemiologist at Harvard, estimates that SARS-CoV-2 could infect up to 70% of the world’s population within a year.
While this may sound dire, it’s not entirely bad news. One good thing to keep in mind is that SARS-CoV-2 infection is clearly not as severe as it once seemed. Early estimates of death rates around 2-3% are likely much higher than the true mortality rate once all the mild cases are considered.
Most of the deaths due to COVID-19 are occurring in our already most vulnerable populations—the elderly and those with other ailments such as cardiovascular disease and diabetes. That’s not to say that these aren’t people worth protecting, it’s just that it’s easier to manage pockets of the community that may be more defenseless than the rest of us.
As more cases are reported across the globe in the coming weeks, remember to take case numbers and mortality rates with a grain of salt–actually take them with a huge hunk of rock–because testing capacity and reporting criteria differ regionally. There is no doubt that there are more than 128 cases of COVID-19 in the U.S. There is also no doubt that the mortality rate is actually far lower than what’s being reported today. The former is bad, the latter is good (prime example of well-balanced journalism here folks).
The question remains what do we do with this information? I won’t go so far as to tell you that COVID-19 is a nothingburger that will blow over, nor will I declare doomsday. I recognize that this is neither reassuring nor discouraging, but it is where we find ourselves today.
So, it’s still not time to worry.
If you are sick, isolate yourself. A face mask may help to prevent you from infecting others. If you require medical attention, call your doctor’s office before visiting. Do not visit your elderly family members and stay away from assisted living facilities when you are unwell. Be aware of illness around you and use common sense.
More resources:
A Mysterious Case of COVID-19 Has Appeared in the U.S. What Do We Do Now?
Five Myths About Coronavirus Debunked
CDC Coronavirus Disease 2019 (COVID-19)
STAT News – Coronavirus