[author: Pamela Koenig]

Photo by CDC on Unsplash

Intranasal vaccine may be our best weapon in the battle to obliterate COVID-19 and other potential future pandemics.

Animal studies have shown that a more widespread immunity is produced with an intranasal vaccine than an intramuscular injection. For example, both influenza and SARS-CoV-2 are airborne respiratory infections that are primarily transmitted through the nose to the lungs. However, where they replicate is the critical point for COVID-19. While influenza and similar viruses replicate in the lower respiratory tract and lungs, SARS-CoV-2 and similar viruses replicate in the nose and upper respiratory tract. Viruses that replicate in the nose make the nose a reservoir for infection, and conventional intramuscular vaccines fail to eradicate viral replication in the nose. Consequently, the host may be susceptible to reinfection and may still transmit the virus to others. Intranasal vaccines not only develop strong protection in the lungs, they also build mucosal immunity in the nose, effectively shutting down nasal viral replication and transmission.

Intranasal vaccines have additional advantages. They are more stable and more easily stored than conventional injections, which may require storage and shipping at low temperatures. Furthermore, conventional vaccines are given intramuscularly, sometimes requiring 2 doses, whereas intranasal vaccines are given once intranasally with a pre-filled syringe or sprayer and may even be self-administered. Intranasal vaccines also have the advantage of being able to deliver a high concentration of the agent directly to targeted sites of infection, while limiting side effects on normal cells.

There are two FDA approved intranasal liquid vaccines, FluMist and Nasovac, currently on the market for influenza. Other liquid vaccines for intranasal administration have been studied for infectious diseases with promising results, including measles, meningitis, tuberculosis, viral gastroenteritis, and pneumonia. Dry powder formulations, which have the advantage of being relatively more stable than liquid vaccines, have recently been explored in clinical trials as next generation intranasal vaccines.

Utilizing data from animal studies and the previous work on the intranasal flu vaccines, researchers in Britain, Hong Kong, and the U.S. have developed intranasal vaccines for COVID-19, which are currently in human clinical trials. Prophylactic treatment with an intranasal vaccine for COVID-19 has huge implications. Since initial replication in the nose is restricted after intranasal administration, individuals exposed to the virus would most likely rapidly eliminate it; if contracted, the disease would not progress, at most, beyond mild symptoms. This factor is particularly important to vulnerable individuals at high risk for severe disease in the population, such as older adults, people with comorbidities, and the immunocompromised. Moreover, the rapid reduction of the virus in the nasal passages would make transmission to others unlikely, halting community spread of the virus. The jury is still out on whether conventional injected vaccines, which do not eradicate SARS-CoV-2 replication in the nose, will be effective in stopping the transmission of the disease.

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