Increasingly there is evidence that even though COVID-19 is more deadly than seasonal flu, many of us mount an immune defense leaving us asymptomatic.
A PCR test is positive for a limited time, primarily around the time of symptoms, so PCR based data, while definitive, is rarely applied for the asymptomatic and would most likely under-report COVID-19 as we test too far before or after that temporal sweet spot. Evidence of our immune system responding to COVID’s presence, found in antibodies in our serum, lasts for more extended periods and may give us more accurate but still unreported values. Several studies have looked for the presence of COVID-19 in specific populations, like first-responders. The current research tries to get a more inclusive community snapshot using individuals coming into the healthcare system for elective reasons, checkups, or elective surgery. Yes, it is not generalizable, but let’s see what we might learn.
The study involved 4841 individuals in Virginia undergoing routine laboratory testing or visits; all screened to exclude symptoms of COVID-19. They were a bit younger, more female, white, and concerned and careful about COVID-19. [1] The outcome was the presence of COVID-19 IgG antibodies.
- 2.2% of the tests were positive for antibodies, with 40% of those cases being Hispanic individuals. With corrections for specificity and sensitivity and state demographics, the overall incidence for asymptomatic COVID-19 was 3.0%.
- After much "mathemagic" involving identifying symptomatic and asymptomatic cases state-wide, the researchers concluded that there were 3-fold more cases unreported than reported. This value is much lower than is being reported in other studies.
Increasingly, COVID-19 seems to be pursuing a more benign course than its initial introduction onto the global stage - less hospitalizations and deaths, but also fewer symptomatic cases. What I found interesting is the risk factors associated with seropositive but asymptomatic COVID-19.
- Younger, less than 50
- Black or African American
- Hispanic
- Medicaid or no insurance
- Multi-family homes
- Contact with a COVID-19 positive individual
- Working outside the home or in a health care setting
Except for age, these are frequently the risk factors associated with symptomatic COVID-19. Among these, the greatest risk of asymptomatic infection was exposure to a positive individual followed by being Hispanic, living in multi-family housing, and requiring Medicaid or having no health insurance – the last two being markers of poverty.
Compared to those who were extremely careful, the somewhat careful and not careful had a lower incidence of seropositivity. Perhaps, concern does not always translate to care, because when compared to those who were very concerned, the not concerned had more asymptomatic cases, the somewhat concerned, fewer cases.
There are multiple risk factors for getting COVID-19, but more and more, it is about contact with an infected individual. Once you are exposed, your risk factors are more determinate of your outcome, asymptomatic, ill, or dead. There is a significant group of individuals who experience no symptoms; they mount a robust immune defense. We still do not have a data consensus on how large a part of our population already has a “natural immunity.” That number might hasten our drive to herd immunity and guide who needs to be vaccinated sooner rather than later.
[1] The average age was 49, two-thirds were women, two-thirds were Caucasian. 40% reported a “high-risk” health condition, 75% lived in a single home, 60% had not worked outside their home since Virginia’s lockdown, 8% had contact with a symptomatic COVID-19 individual, 75% were both very concerned and careful about COVID-19.
Source: Assessment of Seroprevalence of SARS-CoV-2 and Risk Factors Associated With COVID-19 Infection Among Outpatients in Virginia JAMA Network Open DOI: 10.1001/jamanetworkopen.2020.35234
This article was updated due to an editing error on the part of the author.
