As we approach winter virus season, some people may be looking for additional protection against contracting Covid-19 beyond receiving the updated vaccine and wearing a mask. In theory, nasal sprays could be one way to do that, offering an extra layer of defense precisely where the virus enters the body. Ideally, you could use a spray to reduce your risk of infection in the days before, during and after events where you have a higher likelihood of being exposed to Covid.
Several academic labs have developed Covid-specific nasal sprays to try to prevent infection, including both long-lasting vaccines and shorter-acting prophylactics. But those drugs are in the early stages of research, and it may be several years before they’re available.
In the meantime, some people are turning to over-the-counter nasal sprays that claim to protect against several respiratory infections, including Covid, either by creating a barrier in the nose or through more general antimicrobial effects. Some of these sprays are available from online stores and drugstores in the United States; others have been approved for use in different countries and can be purchased from international manufacturers.
None of these products have been approved by the Food and Drug Administration for use against Covid. Instead, the ones for sale in the United States contain ingredients that the F.D.A. previously designated as “generally recognized as safe,” or G.R.A.S., for use as food additives.
The G.R.A.S. designation means that the ingredients can be included in other products without having to obtain approval for each new use. It does not mean that they can be marketed as having medical benefits. The F.D.A. and Federal Trade Commission have sent warning letters and sought injunctions against some nasal spray manufacturers, asserting that the companies have made unverified statements about their sprays’ effectiveness against Covid.
There is some research into how these sprays work against Covid, most of it conducted outside of the United States and often sponsored by the manufacturers. But the studies tend to be small and the results not very compelling, said Dr. Eric Topol, the executive vice president of Scripps Research in La Jolla, Calif. “The main issue is lack of data,” he said in an email. “If they were assessed rigorously in adequate numbers of participants, they may well be helpful.”
A few of the sprays are currently being tested in larger clinical trials. If the results are positive, the manufacturers could request F.D.A. approval, though that is likely years away.
A closer look at the sprays
There are two main ways nasal sprays can potentially block an infection. One is by creating a physical barrier over the cells that line the nasal passages, so that viruses like the one that causes Covid attach to the coating instead of infecting the cells.
These sprays are like “a varnish or a shellac on furniture,” said Dr. Jayakar Nayak, an associate professor of otolaryngology at Stanford Medicine.
Iota-carrageenan is one example of a barrier-forming ingredient that has shown some effectiveness. In a study of nearly 400 health care workers in Argentina, 1 percent of those who used a nasal spray containing iota-carrageenan became infected with Covid, compared with 5 percent of people who used a placebo spray.
The other most common way the sprays protect against Covid is through antimicrobial ingredients that directly interact with the virus, often preventing it from replicating.
Nitric oxide is perhaps the best-studied antimicrobial. Initially, it was tested as a treatment for Covid; studies conducted in England and India showed that a nitric oxide nasal spray reduced levels of the virus in people with mild infections faster than a placebo. However, another study testing nitric oxide gas on cells in a dish found that it failed to stop the virus from replicating.
The company that produces the nitric oxide nasal spray, Sanotize, is now testing whether the spray could be effective as a prophylactic. A preliminary study conducted among students in Thailand found that, following exposure to someone with Covid, 6 percent of people who used the spray eventually tested positive, compared with 26 percent of people who didn’t use it.
“By reducing the quantity of virus at the time of the exposure, the hope would be to then reduce the infectivity and consequent risk of infection,” said Dr. Stephen Winchester, a consultant medical virologist at Frimley Park Hospital in England, who led the research testing nitric oxide as a potential treatment for Covid, which was sponsored by Sanotize.
Other examples of these types of nasal spray ingredients are xylitol and ethyl lauroyl arginate hydrochloride. However, they have primarily been tested on cells in a dish, not in human trials, and the evidence for them is weaker.
In general, the studies investigating nasal sprays are “promising,” said Hector Aguilar-Carreno, a professor of virology at Cornell University who developed an antiviral Covid spray currently being tested in animals. But while the ingredients in the sprays have been deemed safe in other products, they have not been evaluated for use specifically in the nose, he said. “A lot more research is needed before I would feel safe using them.”