Nasal vaccines for Covid-19: How do they work and what are their benefits?

The Drugs Controller General of India (DCGI) approved Bharat Biotech's Covid-19 nasal vaccine, Incovacc, for emergency use in India on Tuesday. Health minister Mansukh Mandaviya announced the development on Twitter.

With this, India will no longer have to depend only on the intramuscular shots that were hitherto available.

What is a nasal vaccine?

There are several methods of administering a vaccine. The most common is the intramuscular vaccine, where the shot is delivered into the muscle. In subcutaneous vaccines, the shot is delivered between the skin and the muscles.

Vaccines may also be delivered orally, as in the case of Polio drops. However, in nasal vaccines, the shot is sprayed into the nostrils and inhaled.

Bharat Biotech's Incovacc will have a two-dose schedule. The first dose would involve a total of 4 drops (2 in each nostril). The second dose will have to be repeated within 28 days. This second dose would also involve a total of 4 drops (2 in each nostril).

Several viruses enter the human body through the mucosa. These tissues line the nose, mouth, lungs, and digestive tract. When it enters the body, the immune cells get activated and flock to the site of infection to stop its spread.

In the case of nasal vaccines, the virus may be stopped from entering the body by attacking it at its point of entry.

How do nasal vaccines work?

When a vaccine is administered to a human body, the B cells in the blood start churning out antibodies. The most important of these are called IgG antibodies. They search for the virus in the body and, with the help of T cells, destroy the infected cells.

B cells, however, also reside around the mucosal tissues. When a nasal vaccine is administered, they form another type of antibody, IgA. IgA with T cells destroys the pathogens in the airway only. Also, they memorise the pathogen and prevent it from entering the body ever again.

What are the advantages of nasal vaccines?

• Cost reduction: These vaccines reduce the administration cost as they do not need syringes and needles.
• Can be self-administered: Nasal vaccines can be easily self-administered. They do away with the dependence on trained individuals.
• Mild symptoms: As the virus is not allowed to enter the body, the symptoms, if any, are mild.

Bharat Biotech has said that the intranasal vaccine has shown "unprecedented" levels of protection in mice, and the data has been published in the journal Nature.

Are there any downsides to nasal vaccines?

According to Nature, besides Polio, mucosal vaccines have not been very successful against other diseases. In many cases, it does not generate a sufficient immune response. It may also trigger side effects.

However, it also stated that data has shown that it is possible to prevent infection and transmission in some animals via mucosal vaccines.