For this reason, groups of scientists, including myself, are working on nasal vaccines against covid. In the best case scenario, a nasal vaccine could enter the mucosal layer inside the nose and help the body produce antibodies that stop the virus before it has a chance to attach to people’s cells. This type of immunity is known as sterilizing immunity.
By trapping viruses right at the site of infection, the antibodies induced by nasal vaccines can give the body a head start in fighting the virus before it causes symptoms. Nasal vaccines may not only be better equipped to prevent infection, but they may also elicit the same kind of immune system protection as other vaccines, and even stronger, because immune memory would be at the virus’s gateway. These vaccines can develop memory B cells that offer high protection and produce faster and better antibodies for future infections and memory T cells, which help kill infected cells and support antibody production.
These types of vaccines have generally been considered more difficult to manufacture. The mucosa layer is a formidable barrier. The body also does not mount a robust immune response simply by spraying any conventional vaccine through the nose. The approved nasal flu vaccine, called FluMist, uses weakened viruses to enter cells in the nose and stimulate an immune system response. But this method is not safe to use in immunocompromised people.
The good news is that some scientists, among whom I am, believe that we have found a way to solve this problem for SARS-CoV-2. We have proven in studies with animals that we can spray so-called virus spike proteins up the nose into a previously vaccinated host organism, and significantly reduce infection in the nose and lungs, and also provide protection against disease and death. Combining this approach with current efforts to develop a single vaccine for a broader range of coronaviruses could also offer people protection against future variants.
A big question is how long immunity from a nasal vaccine would last. So far, in animal studies, antibodies and memory immune cells persist in the nose for months. If this immunity wanes over time, as it does with other vaccines, using the nasal spray every four to six months as a booster — possibly without a prescription — may make more sense in this pandemic. This poses similar challenges to other boosters, where uptake could be much higher, especially among high-risk groups. Encouraging people to get their boosters is vital. But for many people, the reluctance to get a nasal spray booster may be less than a booster that involves a needle injection.
The world urgently needs a vaccine strategy that posts immune guards at the front doors to prevent viral invaders from infecting us. There are several other nasal vaccine approaches in various phases of clinical trials. And any success we have in developing a nasal vaccine against COVID-19 will not be limited to this specific virus. Nasal spray vaccine strategies can also be applied to other respiratory pathogens.
Although some hurdles remain, it is worth focusing on the potential public health and immunological benefits of nasal spray vaccines now and for years to come.
Akiko Iwasaki (@VirusesImmunity) is a professor of immunobiology at Yale School of Medicine and an investigator at the Howard Hughes Medical Institute.