A Nasal Spray Vaccine Could Be Key to Stopping the Spread of Covid-19
Covid-19 vaccines are incredibly good at preventing severe symptoms and hospitalization, but they’re probably less effective at stopping transmission. To do that, we might need a different kind of vaccine altogether.
Because SARS-CoV-2 is mainly transmitted through droplets and airborne aerosols, some scientists reason that a vaccine should provide first-line protection where the virus typically enters the body — the nose. A Covid-19 vaccine that’s sprayed into the nose may not only prevent people from getting sick in the first place but also stop them from spreading the virus to others.
“When you get Covid-19, you don’t get injected with the virus. You get it in your respiratory tract,” Matt Memoli, MD, a virologist at the National Institute of Allergy and Infectious Diseases, tells the Coronavirus Blog. “So, you don’t need antibodies in the blood to prevent infection there. You need antibodies at the site of infection at the mucus membranes, at the airways.”
All vaccines are designed to spur the production of protective immune proteins called antibodies. Most vaccines are injected into the muscle, which stimulates serum antibodies that circulate in the blood. Serum antibodies are generally very effective at protecting against serious disease.
A nasal spray vaccine, on the other hand, generates antibodies that are secreted by the tissue that lines the inside of the nose. Antibodies here can block the incoming pathogen at the site of infection. This type of immunity is known as mucosal immunity. FluMist, a nasal spray vaccine for flu, works this way.
Without protective antibodies in the nose, those who get an injected Covid-19 can harbor viral particles there even if they don’t have disease symptoms themselves. That means it’s still possible for people to pass on the virus even if they’re vaccinated.
The authorized Covid-19 vaccines by Moderna, Pfizer, and Johnson & Johnson aren’t designed to generate mucosal immunity, but there’s some indication that they do. Early data shows that they can reduce asymptomatic cases, which means they provide some level of mucosal immunity, Memoli says. But they likely can’t stop the spread of the virus entirely. It takes a much higher concentration of serum antibodies in the blood to protect the nose compared to the lungs.
One biotech company, Meissa Vaccines of San Francisco, just received a green light from the Food and Drug Administration to begin an early-phase trial of a single-dose, intranasal Covid-19 vaccine. The trial will enroll 130 people, and the company plans to begin enrolling healthy adult participants by the end of March.
“Blocking transmission is really the endgame strategy,” Marty Moore, PhD, CEO and founder of Meissa Vaccines, tells the Coronavirus Blog.
In monkeys, Meissa’s Covid-19 vaccine induced neutralizing antibodies in both the nose and serum. The experimental vaccine was also “highly protective” when the monkeys were intentionally exposed to SARS-CoV-2 in the upper and lower respiratory tract.
Another company working on a nasal spray vaccine, Maryland-based Altimmune, launched an early-stage trial of 180 people in February.
Nasal spray vaccines could be ideal for kids, who don’t get as sick from SARS-CoV-2 as adults do but can still spread the virus.
Even though the Moderna, Pfizer, and Johnson & Johnson vaccines work very well, researchers like Memoli and Moore think next-generation Covid-19 vaccines will be needed in the near future to keep the virus at bay. For one, current vaccines might not be as effective against new variants of the virus. Secondly, immunity to the current vaccines may wane over time.
There’s one major downside to nasal spray vaccines, and that’s the fact that mucosal immunity is generally not as long-lasting as systemic immunity. Memoli thinks an intranasal vaccine could be combined with a shot for maximum effectiveness, or nasal sprays could act as a booster for injected vaccines.
“SARS-CoV-2 is probably going to become endemic,” Moore says. “An intranasal vaccine could be an important strategy to really put this to bed and get back to normal.”