The Drugs Controller General of India Friday approved the trials of intranasal booster doses against Covid-19 that is being manufactured by Bharat Biotech, the maker of Covaxin. The two trials, approved by the Central Drugs Standard Control Organisation, will evaluate the intranasal vaccine in several hundred volunteers both as a standalone two-dose vaccine and as a booster vaccine for recipients of Covaxin or Covishield. While most vaccines throughout history have been jabbed into the upper arm, when it comes to protecting people against pathogens that invade the airway — like the novel coronavirus — an intramuscular shot isn’t necessarily the only strategy available. The importance of such a dose would be that it'd be easier to administer in mass vaccination drives, thereby helping in larger coverage in a relatively lesser period of time. So, what is an intranasal vaccine? Vaccines are usually given through different routes, with the most common being injectable shots delivered into the muscles (intramuscular) or the tissue just between the skin and the muscles (subcutaneous). Other routes of delivery, especially in some vaccines for infants, include administering the liquid solution orally instead of injecting. In the intranasal route, the vaccine is sprayed into the nostrils and inhaled. Many viruses, including the coronavirus, enter the body through mucosa — wet, squishy tissues that line the nose, mouth, lungs and digestive tract — triggering a unique immune response from cells and molecules there. Intramuscular vaccines generally fail at eliciting this mucosal response, and instead rely on immune cells mobilised from elsewhere in the body flocking to the site of infection. Experts believe an intranasal vaccine will act against the virus from the time it tries to break the body’s barrier, thereby making it more effective than the intramuscular ones in many cases. How does this vaccine work? Generally, both the aforementioned types of vaccines trigger a response in the blood. B cells, for example, would churn out antibodies — including a particularly potent disease-fighter called IgG — to roam the body in search of the virus. Other cells, called T cells, would either help B cells produce antibodies or seek out and destroy the infected cells. However, vaccines that are injected through the nose or mouth would also tap into another set of immune cells that hang around mucosal tissues. The B cells that reside there can make another type of antibody, called IgA, that plays a large role in destroying the airway pathogens. In addition to this, the T cells that are residing nearby will be able to memorise the pathogens that it encountered and will lifelong scout the areas where these were first encountered. The effectiveness of an intranasal vaccine was first seen in the 1960s when polio doses replaced its injected predecessor. It targeted the body’s immune response in the gut, where the virus thrives and many people who took the oral vaccine seemed to cancel out the infections even before they felt symptoms. The importance of such vaccines These vaccines aim to overcome potential difficulties with mass vaccination and reduce the cost by doing away with the need for needles and syringes. Intranasal vaccines are also expected to cut down on the dependence on various trained personnel to administer the vaccine, according to experts. “Let’s not forget that, with the scale of the pandemic, just the logistics of actually shipping a vaccine, having it available and then having people trained to give an injection in the arm is not so easy. So, one attraction with the intra nasal vaccine is that it’s very simple to use — you just squirt it into your nose — and it’s something that can be self-administered in pandemics and outbreaks,” said Dr Davinder Gill, former CEO of Hilleman Laboratories. Speaking about the importance of developing intranasal shots, vaccine scientist Dr Gagandeep Kang explained: “It’s an easy-to-deliver vaccine. Moreover, as it is going into a mucosal surface, it will likely be restricted (and there is a) likelihood of lower safety events.” However, are there any drawbacks? Vaccines that arouse mucosal immunity come with their own drawbacks. It was first noted after the rollout of the oral polio vaccines where in some cases, it still caused the disease after the weakened virus in the product mutated. Also, there is very little evidence to back the effectiveness of this route of delivery so far and, save for some flu vaccines, attempts to deliver vaccines have not been successful, according to experts. “Despite the theoretical advantages, the intranasal approach for vaccination is largely unproven. While this concept has been tested quite extensively in animals, whether this holds true in humans is still largely untested and so the clinical trials here will definitely have to be watched closely,” said Dr Gill. Newsletter | Click to get the day's best explainers in your inbox
