Traditional vaccines are generally injected into muscles. They stimulate antibodies and immune cells that circulate in the blood, protecting major organs and reducing the risk of serious illness. However, relatively few of these immune cells reach the mucosal tissues lining the respiratory tract, where many viruses first enter the body.

Respiratory viruses often enter through the nose and throat, allowing infected people to spread them before the immune system fully responds. Nasal vaccines are designed to strengthen immunity directly at these entry points. By delivering a vaccine through the nose, scientists hope to create a reservoir of specialized immune cells in the airways. These cells could quickly recognize pathogens, block infection, and reduce transmission to others.

So far, only one nasal vaccine has been approved in both the United States and Europe. The live attenuated influenza vaccine (LAIV), marketed as FluMist or Fluenz, has been given to children since the early 2000s. Nasal or inhaled COVID-19 vaccines have also been approved in China and India, although their effectiveness remains uncertain. Researchers are now developing nasal vaccines against pneumonia, pertussis, and other respiratory diseases.

Despite their potential, nasal vaccines are difficult to develop. In 2025, a late-stage trial of an intranasal vaccine against respiratory syncytial virus was discontinued due to underperformance. One major challenge is that the respiratory tract encounters harmless substances such as dust, pollen, and fungi every day. Scientists must therefore produce an immune response that is strong enough to fight viruses without overreacting to harmless particles.

Developing nasal vaccines remains difficult, and many previous attempts have failed to provide strong or lasting protection. Still, their potential to stop viruses at their main entry point continues to attract researchers and pharmaceutical companies. If successful, nasal vaccines could become an important tool against future respiratory diseases.