COVID-19: Nasal vaccines can be a possible game changer, but it has its drawbacks

• Trials to produce nasal vaccines are underway in India.
• A significant advantage of intranasal vaccines is that it creates a robust immune response at the site of virus entry.
• But a disadvantage is their inability to produce effective, long-lasting immunity.

Trials to produce nasal vaccines are underway in India, and this “could be a game changer for children,” according to World Health Organization’s (WHO) chief scientist Soumya Swaminathan. BBV154, an intranasal vaccine developed by Bharat Biotech, is already in the pre-clinical trial phase.

However, this could take some time to develop. And while the speculation is rife that the third wave will affect children more severely, most senior doctors believe that it will not be the case. It is, however, best to err on the side of caution.

Business Insider consulted with Dr Vipin M. Vashishtha — former convener, IAP Committee on Immunisation, and paediatrician at Mangla Hospital and Research Centre, Bijnor, UP — to tell us more about the intranasal vaccine and weigh its pros and cons.

According to Dr Vashishtha, the injection vaccines used now prompt an extensive immune response by producing circulating Immunoglobulin G (IgG) antibodies that offset pathogens even before they can cause severe tissue damage. But IgG is not particularly good at controlling viral entry into the body. This is why most current Covid vaccines fail to provide reasonable protection against transmission, and a vaccinated person can pass on the virus to another person. That’s why these vaccines are called ‘leaky vaccines’.

To block transmission, you need a ‘mucosal immune system’ which produces secretory Immunoglobulin A (IgA) at the site of viral entry (in the nose and oral cavity), and in more volume compared to any alternative type of immunoglobulin in the body. Essentially, IgA is better equipped to dominate the early stage of infection and neutralise viruses when compared to IgG. It has been observed that IgA-mediated mucosal immunity could decrease the infection-causing ability of the virus, thereby reducing transmission.

A strong immune response as virus enters

A significant advantage of intranasal vaccines is that it creates a robust immune response at the site of virus entry -- the nose. This helps in shielding against the virus and transmission. If the virus can be stopped from entering at this point, it will not be able to get into the lungs to cause damage. If an effective mucosal immune response is generated, it would possibly prevent the coronavirus infection from the outset and more effectively reduce transmission of the virus.

These vaccines will be easier to store, transport, and administer. Some of these vaccines may be stable at room temperature, making them easier to ship and potentially improving access to vaccination in remote areas.

It is easier to administer in the form of a nasal spray, and being non-invasive and needle-free, children and people unable to cope with the sight of a needle may benefit from this. It can also be used on both children and adults.

The question of long-lasting immunity

On the flip side, these intranasal vaccines do have some drawbacks also. Though they induce both IgA and IgG antibodies, thereby potentially providing ‘sterilising immunity’ in the upper respiratory tract (‘local immunity’), it is seen with some candidates that systemic IgG antibodies are not as robust in the lower respiratory tract as at upper airways.

Another drawback is their inability to produce effective, long-lasting immunity that results in a faster waning of immunity.

Though this route seems more suitable for the administration of vaccines to young children, in practice, however, it is noticed with intranasal flu vaccines that kids sneeze right after administration that makes this far too risky an attempt for something so virulent and lethal. Seasonal allergies in young children also resist smooth administration.

Another issue is the safety of these vaccines. Since, the live attenuated virus (a virus weakened in a way that it cannot produce disease in an individual) is employed in these vaccines, there is a rare risk of reversion of neuro-attenuation, meaning that the virus can regain its ability to cause disease in the individual. This extremely rare phenomenon was observed in the oral polio vaccine also. Proving the safety of live attenuated vaccines takes a long time. One type of intranasal flu vaccine by a Swiss company, Berna Biotech, was discontinued after being linked with a higher risk of Bell’s Palsy.

Considering the current availability of different vaccines and the level of and the type of immunity that all provide (exclusively being IgG type immunity) mucosal or IgA type needed for complete protection against COVID-19, it seems both types of vaccination are going to be necessary for absolute immunity. According to Dr Vashishtha, “this would have the highest possible protection. Both against the severe disease involving lungs and transmission of disease from one person to another.”


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