The first generation of COVID-19 vaccines are being rolled out across the world in a bid to bring the pandemic under control. But in parallel a next generation of vaccines are also in development which include intranasal sprays, which hold great promise of broadening the reach of different types of vaccines.
This is because nasal vaccines boost our immune response in the mucosa of the nasopharyngeal area (the nose and throat), which is where the coronavirus first enters the body, and when people are most infectious.
The current COVID-19 vaccines have been shown to be highly safe and effective. Distributing them however comes with challenges: all of them require refrigeration, with some mRNA vaccines requiring ultra-cold refrigeration, and this can be a logistical problem in countries without adequate infrastructure, equipment or electricity supply.
Nasal spray vaccines for other diseases already exist and offer several advantages. For COVID-19 the nasal spray vaccines being tested don’t require any refrigeration, nor do they need to be given by trained health workers like injections do. Since they are designed to be used like nasal congestion sprays people would be able to self-administer them at home. The other big advantage is that they are likely to be more popular for the millions of people who don’t like needles.
But besides the ease of use, there’s an even more important potential advantage. It is possible that they are even better than the current injectable vaccines at stopping transmission. This is because nasal vaccines boost our immune response in the mucosa of the nasopharyngeal area (the nose and throat), which is where the coronavirus first enters the body, and when people are most infectious.
Injectable vaccines trigger a systemic immune reaction to the virus, but the nasal spray triggers mucosal immunity – this could cut the infection short just when people are most likely to spread it, and also before it has a chance to infect the rest of the body.
Such immunity might also confer an advantage against new variants as it can stimulate a broader immune response than injectable vaccines that target a specific part of the coronavirus – if the virus mutates in that target, there’s a chance the vaccine is less effective.
There’s a precedent for focusing on mucosal immunity – the oral polio vaccine also stimulates mucosal immunity, except this time in the gut, which is where the poliovirus can sometimes live.
Nasal spray vaccines being tested
In April, an experimental nasal spray vaccine that could protect against both influenza and COVID-19 will start phase 1 trials in Hong Kong. The vaccine, supported by the Coalition for Epidemic Preparedness Innovations (CEPI), uses a weakened flu virus in which the NS1 protein (that allows the flu virus to get past its infected host’s defences) has been deleted and replaced with part of the spike protein of the SARS-CoV-2 virus.
Also, in January 2021, phase 1 trials of a nasal vaccine called COVI-VAC began in the UK. The vaccine is being tested on 48 healthy volunteers with results expected by the middle of the year.
In the USA, last month a company called Altimmune launched a phase 1 trial of an intranasal vaccine called AdCOVID, and other nasal vaccine candidates are also being tested in China and India.
Ultimately, this isn’t about pitting injectable vaccines against intranasal ones – it's about having as many weapons against COVID-19 in our armoury as possible. The more options we have, the more likely we are to be able to bring the pandemic under control.