Results from China, Japan, and USA show that half or more of asymptomatic cases have lung damage
Asymptomatic cases show a weaker immune response. In a small study in China, the asymptomatic cases had a lower, slower immune response, which means they shed virus for longer than the symptomatic cases, perhaps even as long as 14 days. Though the presence of viral RNA does not necessarily mean they can infect other people. It may be fragments of the whole virus.
a, CT scan of a 45-year-old female showing focal ground-glass opacities in the lower lobe of the left lung (arrow). b, CT scan of a 50-year-old female showing ground-glass opacities and stripes coexisting in the lower lobe of the right lung (arrows).
Below, a Scripps review found the rate of lung damage was as high as 70% of asymptomatic cases. Both these studies are small, non randomized, retrospective studies.
It’s not surprising that people might not notice that their lungs were underperfoming. We have so much extra lung capacity for day to day living that many people don’t notice damage. In cases of lung cancer, people are often not diagnosed until they are in an advanced late stage. Presumably, humans hardly ever push their lungs to the limit now, so we don’t notice if they are not performing at peak.
What Does Asymptomatic COVID-19 Look Like Under the Surface?
Molly Walker, MedPage
Asymptomatic individuals carrying SARS-CoV-2 shed the virus longer than those with COVID-19 symptoms, with other lab findings suggesting the symptomatic patients mounted more robust immune responses, a small study in China found.
Virus-specific IgG antibody titers and cytokine levels were also significantly lower among asymptomatic patients in the acute phase of infection, when viral RNA can be found in respiratory specimens, the authors wrote in Nature Medicine — both of which indicated that immune responses weren’t as strong in the asymptomatic group.
For the study, they examined data from 178 patients with PCR-confirmed SARS-CoV-2 infection in the Wanzhou District in China, including 37 without symptoms. Median age in the latter was 41, and 22 were women.
Lab tests show there was lung damage in just over half the group, inflammation (CRP), and there was some liver damage (ALT):
Lab values and imaging were not entirely normal for the asymptomatic group. Eleven had increased C-reactive protein levels (CRP) and six had elevated levels of alanine aminotransferase (ALT). Chest CT found “focal ground-glass opacities” in 11 and “stripe shadows and/or diffuse consolidation” in another 10 of the group; in two-thirds of these 21 patients, the abnormalities were in only one lung. The remaining 16 showed entirely normal imaging.
Antibody levels fell faster in asymptomatic people
In the early convalescent phase, defined as 8 weeks after hospital discharge, symptomatic patients had higher IgG levels, though both groups experienced over 90% decreases in IgG levels. A larger proportion of asymptomatic patients had decreases in neutralizing serum antibody levels versus symptomatic patients (81.1% vs 62.2%, respectively).
These findings should serve as a caution against assuming prior infection confers immunity to future infection, Qiu and colleagues said.
A Scripps study out a few days ago also suggests in people with no symptoms, Coronavirus may be damaging lungs. When they did a CT scan of asymptomatic people on the Diamond Princess, as many as 70% showed some lung damage.
CT Scans show lung injury in asymptomatic carriers of Covid-19
The authors also conclude that the absence of symptoms may not imply an absence of harm. CT scans conducted on 54% of 76 asymptomatic individuals on the Diamond Princess cruise ship, appear to show significant subclinical lung abnormalities, raising the possibility of SARS-CoV-2 infection impacting lung function that might not be immediately apparent. The scientists say further research is needed to confirm the potential significance of this finding.
CT = Computed Tomography.
They estimate up to half of Covid patients may be asymptomatic, though this is contested. A big problem with estimating the rate of asymptomatic infections is that very few studies follow the patients for two weeks to find out if they do develop symptoms. Asymptomatic cases may be just presymptomatic. Another recent review considered only studies with follow up, and pooled the results to find only 15% were true cases of asymptomatic infection. (More on that later).
REFERENCES
Ran and Topal, (2020) Annals of Internal Medicine.