Higher lymphocytes in asymptomatic cases may help resolve infection quicker, reveals study

COVID-19 indoor transmission: Ways to prevent spread of COVID-19 at homes, offices caused by ventilation systems

While asymptomatic patients could reportedly spread the infection as well as symptomatic ones, it is still hard to identify them, let alone understand the clinical characteristics of this infection.

The structure and cross-sectional view of Human Coronavirus. It shows depicting the shape of coronavirus as well as the cross-sectional view. Image shows the major elements including the Spike S protein, HE protein, viral envelope, and helical RNA. Image credit: Wikipedia

Since the outbreak of COVID-19, asymptomatic infections have been a major concern for healthcare practitioners and public health experts. According to current estimates, about 45 percent of all coronavirus patients do not show any symptoms of the disease.

While asymptomatic patients could reportedly spread the infection as well as symptomatic ones, it is still hard to identify them, let alone understand the clinical characteristics of this infection.

According to research done at the American Society for Microbiology, asymptomatic people show a slightly different immune response as compared to those with symptomatic infection. The findings of the study are published in mSphere, an open-access journal published by the American Society for Microbiology.

Asymptomatic v/s symptomatic patients

The researchers enrolled 25 asymptomatic and 27 symptomatic COVID-19 patients in Wuhan, China to study the clinical characteristics of the infection in both sets. Both the groups of patients were of comparable age, gender and comorbidities. Here is what they found:

  • Asymptomatic people had the same viral load as symptomatic people.
  • Those with asymptomatic infection showed viral clearance earlier than symptomatic patients. 
  • The former also had a shorter period of hospital stay – a median of nine days – as compared to those with symptomatic infection – 26 days. 
  • Asymptomatic people had lower IgM antibody levels than symptomatic people, though both groups had the same amount of IgG antibodies. The authors suggested that this was either because asymptomatic people had acquired the infection earlier or because they had a compromised IgM production.
  • Those with asymptomatic infection had a higher level of lymphocytes, basophils and eosinophils (various types of white blood cells that fight infection) and a statistically significant level of CD4+ T cells than symptomatic patients.  
  • Interestingly, no significant difference was found in the cytokine levels of the two groups. This is in contrast to the previously reported studies that associate higher cytokine levels with severe disease. Then again, the symptomatic patients enrolled in this study had mild to moderate infection only. 

The authors of the study indicated that while some cytokines can be used to predict severe disease, the prediction might not be as effective when asymptomatic cases are taken into account. Additionally, the symptomatic patients also showed liver damage which did not occur in asymptomatic people.

Limitations of the study

The study authors pointed out the following limitations in the study:

  • The sample size is very small.
  • The dynamic immunological changes were not noted in the asymptomatic group.
  • Even though the study compared some factors in the immune response, more difference in the immune response still remains unknown.

In other words, more studies are still needed to better understand the pathogenesis of COVID-19 and find strategies for disease control.

Until then, it is important to trace and test all the possible cases, maintain physical distance, wear masks and follow hand hygiene to keep the public safe from the infection.

For more information, read our article on Asymptomatic transmission of COVID-19

Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.

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