A nasal vaccine, one expert said, is a "fantastic idea" for two reasons -- one, it can potentially create sterile immunity, and two, it is easy to administer and thus scalable, reported rediff.com. Bharat Biotech is working on a three-legged clinical trial for its intranasal vaccine BBV154, which is in phase two. The Hyderabad-based firm is testing the efficacy of a combination in three modes -- two intranasal shots, first a Covaxin shot followed by the nasal vaccine, and Covaxin following a nasal shot. Also read: AIIMS to begin Phase 2/3 trials of Bharat Biotech’s nasal Covid-19 vaccine within couple of weeks: Reports The idea is to see which combination induces better and long-lasting immune response. Therefore, the intranasal vaccine could be used as a combination with the intramuscular Covaxin shot. "While the nasal vaccine can be administered as two shots, the company is testing whether combining it with Covaxin gives better results. Thus, this can be used as a mix-and-match with Covaxin to produce a more holistic immune response," the source said. The two vaccines have different mechanisms of action and trigger slightly different immune responses. Dr Shahid Jameel, senior virologist and director at Ashoka University, said a different kind of antibodies protects the nasal mucosa -- these are called IgA antibodies. "This is not sufficiently generated when a vaccine is administered through the intramuscular route," Jameel said. Also read: Killing off Coronavirus: Nasal spray developed by Bangladesh to ‘hit market soon’ Commenting on the nasal vaccine, Dr Jacob John, former head, Centre for Advanced Research in Virology at the Indian Council of Medical Research, said to have a nasal vaccine is a "fantastic idea" for two reasons -- one, it can potentially create sterile immunity, and two, it is easy to administer and thus scalable. Experts feel that when one gets sterile immunity in the nasal tract, one does not shed the virus, and this prevents transmission. According to sources in the know, recruitments for the phase 2 trials are over. Around 650 volunteers are likely to be part of the trials. The first phase had 175 participants. Meanwhile, Bharat Biotech has also finished administering the vaccines for its paediatric trial of Covaxin. Now, it is analysing the data before it can submit it to the regulator for review.