A review on COVID-19, colonising microflora and microbial links to age-related differences and off-target effect of live vaccines like BCG

Abstract

Age-related expression for a disease is well known. The applicability of such an expression for SARS-CoV-2 prompted this review. Whenever an infection is highly prevalent, the younger age groups get more affected. But this is not seen in COVID-19. The severity of COVID-19 disease is more and sometimes fatal in adults when compared with children and found to be less severe. This shows a striking difference as generally children tend to get more affected with most of the respiratory viruses.Can this be explained by the differences that are observed in their oro-pharyngeal, lung, nasopharyngeal and gastrointestinal microbiota? This review addresses the potential of resident microbiota for the spectrum of expressions in susceptible population through various mechanisms. In the nasopharynx, where microbial interactions and competition may limit the growth of SARS-CoV-2, children are more extensively colonized with viruses and bacteria than adults. One study found no discernible differences in the nasopharyngeal microbiota between SARS-CoV-2 patients and healthy individuals, whereas other investigations found significant differences in the oro-pharyngeal, lung and gut microbiota between these groups.There is a reduced load of bacteria in the gut microbiota of the patients who are infected with COVID-19; especially the bacterial phyla such as are found to be very less in the gut but there is relatively a higher load of other organisms such as It is known that have a lot of anti-inflammatory properties and show decreased gastrointestinal ACE-2 expression. The microbiota in the human gastrointestinal tract differs with age. Children’s guts exhibit higher concentrations of These variations in the gut microbiota of patients have also been noted between those who do and those who don’t excrete SARS-CoV-2 in their feces. However, these results, which are based on the gut flora of each patient, may be affected by factors like food, age, use of antibiotics and their immune system. This relation between the gut microbiota and the severity of COVID-19 disease in patients is studied and it is still unclear. Randomized control trials (RCT) of BCG are being conducted to lessen the severity of COVID-19. Oral polio vaccination and the measles-containing vaccine (MCV), in addition to BCG, have been proposed as potential factors in the difference in COVID-19 severity. To lessen the severity of COVID-19, a randomized control trial of the MMR vaccine has been planned. Understanding the mechanism underlying the age-related variations in COVID-19 severity through the colonizing microbial flora and off-target effects of live vaccines (BCG, etc.) would provide important cognizance and open up many opportunities for the management and cure of this novel infection.