Nasal vaccines for COVID-19 offer hope and face hurdles

Jabs in the arm may not be as good at preventing transmission as nasal spray vaccines, some scientists suspect. The shots are better at building defenses that circulate in the blood or fluid that surrounds cells, which makes them great at protecting the lungs. CDC/Douglas Jordan via Wikimedia Commons

A few weeks ago, I was obsessed with my nose and throat. I was on a trip to Seattle to speak at a small, masks-required virology meeting about being a journalist during a pandemic. I went to graduate school there, so I was thrilled to see old friends and colleagues. But the irony that I was risking getting infected amid rising COVID-19 cases to get on a plane to talk with virologists about the pandemic didn’t escape me. I spent the whole week on high alert for the slightest hint of a sore throat or a runny nose. Despite masking, I worried that I’d get sick and be stuck thousands of miles from home or that I’d unknowingly pass the virus on to someone else.

Luckily, this story has a happy ending. I didn’t catch the coronavirus. None of my friends or former colleagues got sick. Although I didn’t escape completely unscathed; I did come down with a mystery, non-COVID cold that I suspect I caught from a friend’s baby. Still, the experience made me wonder ​​— what if I didn’t have to worry so much about becoming a disease spreader because there were COVID-19 vaccines that helped my body control the virus in my nose?

Researchers are working on vaccines that would hopefully do just that. You squirt these vaccines into your nostrils, rather than inject them into your arm muscle like the current COVID-19 shots. Sprayed up the nose, the vaccines teach our immune systems to fortify our nostrils against coronavirus, perhaps meaning we get less sick or making us less likely to transmit the virus to other people.

Jabs in the arm may not be as good at preventing transmission as nasal spray vaccines, some scientists suspect. The shots are better at building defenses that circulate in the blood or fluid that surrounds cells, which makes them great at protecting the lungs. And they have done what they are designed to do: curb severe disease and death (SN: 8/31/21). Booster doses help fend off severe COVID-19 better than the first two shots — especially for older people, studies show (SN: 4/29/22). But even with death rates down, that doesn’t mean our fight with coronavirus is over. Waning immune defenses combined with slippery versions of the coronavirus that can evade parts of our immune systems leave vaccinated people susceptible to infection. So we still need additional protection.

A panel of experts advising the U.S. Food and Drug Administration will meet later this month to weigh in on whether we might need a vaccine update for the fall. Updated shots may indeed be on the horizon: Preliminary data from vaccine developer Moderna show that its latest vaccine, which includes both omicron and the original virus, boosts the immune response against omicron as well as other variants such as delta, the company announced on June 8.

And on June 7 the FDA advisory committee recommended that the agency authorize a new COVID-19 vaccine for emergency use. This one, developed by the company Novavax, is based on a traditional method —  showing the immune system purified viral proteins — which may be appealing to still unvaccinated people who are hesitant about the novel mRNA technology in Moderna’s and Pfizer’s shots (SN: 1/28/21). Other experts are working on vaccines that might hold up against an onslaught of variants, both present and future.

And then, there are the nasal spray vaccines. They could not only protect our lungs, but also the mucous membranes that line the upper regions of our respiratory tracts such as the nose. Such sprays would give us not only a motion detector ready to sense an intruder in an inner room of a building but also an alarm system that goes off the second the front door opens.

That type of alarm system isn’t a brand-new tool. For example, there is a nasal influenza vaccine available in the United States called FluMist, which teaches the body to recognize four different strains. And there is a similar one in Europe called Fluenz Tetra. Each flu virus included in these vaccines is weakened but can replicate in the body. The attenuated viruses grow best at cooler temperatures found in our noses, not the warm environment of our lungs, a barrier that keeps them from making it to the lungs and causing influenza. But by taking off in the nose, replicating viruses kick off an immune response, so our bodies learn to set up reinforcements there.

Already roughly a dozen potential COVID-19 nasal vaccines have made it to clinical trials around the world. One developed by a company called Altimmune was abandoned after early results showed the vaccine didn’t prompt a good immune response in healthy participants. Others have shown promise when tested in animals.

The prospect of having nasal vaccines that may be able to curb transmission better than existing shots is understandably exciting. But these types of vaccines still have a way to go before hitting local pharmacies or doctors’ offices.

First, it’s crucial for the nasal vaccines to strike the right balance. Their sprays must be strong enough to provoke our immune systems, but still weak enough that there aren’t unwelcome symptoms or side effects. It’s also of course important to ensure the safety of vaccine candidates that include live, weakened viruses.

Some nasal vaccine candidates are similar to the influenza vaccine and include live, weakened viruses. Most of these viruses aren’t the coronavirus itself, but rather harmless-to-human viruses that sport one coronavirus protein for our bodies to recognize. Others may not need a virus to grow in the body to work. One team is developing a nasal spray that includes only the coronavirus spike protein, which helps the virus break into cells. That spike spray could serve as a boost for people who received one of the mRNA vaccines, coaxing important immune cells to come live in the nose and other parts of the respiratory tract. Once there, those immune cells would be poised to kick into high gear if the coronavirus invades.

Second, nasal sprays face the same problem as current COVID-19 vaccines. What happens when the virus evolves in ways that help it hide from our immune system? We’ve already seen the consequences of that thanks to the delta and omicron waves that raced around the globe. And from 2016 to 2018, FluMist stumbled in the face of tweaked versions of some influenza viruses. Experts recommended that people get a different type of flu shot in those seasons. Just as researchers are considering updating existing COVID-19 shots to better mimic the viral variants currently wreaking havoc, nasal vaccines may also need regular updating.

If I had a choice, I would never catch coronavirus. But in the grand scheme of things, it’d be nice if a spray up my nose could drastically lower my chances of passing it on to someone else if I did get infected. If they make it to consumers, the nasal vaccines could make future COVID-19 waves much smaller than they are now. And after more than two years of navigating ever-larger waves, wouldn’t that be nice?

This story was originally published by Science News, a nonprofit independent news organization.