COVID-19 has been infecting people around the world for more than two years. Many people still get the virus even though they have received as many as four vaccinations. Chiang Kuan-yu, a doctor of the Taipei City United Hospital in Taiwan, said that the “mucosal vaccine” given in the form of a nasal or oral spray can help activate immune cells in the respiratory tract and may be more effective in preventing infection than intramuscular (IM) vaccine injections.
The SARS-CoV-2 virus infects the mucosal surfaces of the nose and lungs and thus, the mucous producing surfaces are the first line of defense against pathogens.
The mucosal vaccines are different from injectable vaccines. Chiang said that the “mucosal vaccine” has an important feature—it preferentially promotes the production of secretory immunoglobulin A (IgA) in nasal secretions that can neutralize the virus.
He pointed out that although the intramuscular vaccine can reduce the severity of cases and the hospital admission rate, it cannot prevent mild illness or transmission of the virus.
He explained that when the vaccine is injected into the muscle, it triggers an immune response that activates B cells to produce antibodies and T cells. But the antibodies are not enough to provide immediate and rapid protection.
The immune cells in the respiratory mucosa, called tissue-resident memory T cells and B cells, function slightly differently from circulating T cells and B cells found in the blood and lymph. They produce secretory IgA, antibodies that are intertwined with the layers of the respiratory tract and are able to deter pathogens instantly.
Chiang pointed out that some mucosal vaccines are packaged into aerosols and inhaled through the mouth with a sprayer. The dose is one-fifth the amount of an injected vaccine.
Mainland China and India approved COVID-19 mucosal vaccines earlier this month that are administered by oral inhalation and nasal spray respectively.
According to the World Health Organization (WHO), mucosal vaccines can generate an immune response in the mucous membranes of the respiratory tract and are therefore expected to be capable of preventing infection and the spread of the virus.
The WHO has not yet approved use of the mucosal vaccine. The organization needs to see more vaccine-related data in order to assess its efficacy.