Mucous membranes of the nose and mouth might play a “significant role” in curbing the spread of COVID-19, say scientists, in an analysis published in the journal Frontiers in Immunology. The researchers call for more studies to evaluate the role played by the mucosal immune system in asymptomatic and mild states of the coronavirus infection.

“We think it is a serious omission to ignore the mucosal immune response to SARS-CoV-2, given its initial sites of infection,” said Michael W. Russell, a co-author from the University at Buffalo in the US, as per PTI reports.

“Clearly the response of the systemic immunoglobulin G antibody — the most abundant circulating antibody — is important, we do not deny that, but on its own it is insufficient,” Russell added.

According to him, the initial focus of COVID-19 research was on cases of severe disease when the virus descends into the lower respiratory tract, especially the lungs, where the cellular immune response worsens the inflammation rather than fighting the infection. But since the upper respiratory tract is the initial point of infection for the SARS-CoV-2 virus, the immune responses that are triggered there are key in the study of the disease.

The researchers believe the high rate of asymptomatic transmission of COVID-19 is another reason why mucosal immunity is so important, PTI reported.

“Given that many infected people remain asymptomatic, and that a large number of those who develop symptoms suffer only mild to moderate disease, this suggests that something, somewhere, does a fairly good job of controlling the virus,” said Russell.

More studies are required to determine the nature of mucosal secretory immunoglobulin A (SIgA) antibody responses over the course of infection — including those which are asymptomatic or pre-symptomatic — on both mild and moderate cases of COVID-19 disease, the scientists note, adding that these responses may vary across different demographics. 

They also believe that a focus on mucosal immunity may make possible the development of a type of vaccine, such as a nasal vaccine, that could be easier to store, transport and administer, as per PTI reports.

“The potential advantage of a mucosal vaccine is that it should induce immune responses, including SIgA antibodies, in the mucosal tracts, in this case especially the upper respiratory tract, where the coronavirus makes first contact,” explained Russell, adding that injected vaccines usually do not do this.

“After all, the mucosal immune system is by far the largest component of the entire immune system, and it has evolved to protect the mucosal surfaces where the great majority of infections arise,” he added.