Nasally inhaled therapeutics and vaccination for COVID‐19: Developments and challenges

The nose is the initial site of viral infection, replication, and transmission in the human body. Nasally inhaled vaccines may act as a promising alternative for COVID‐19 management in addition to intramuscular vaccination. In this review, the latest developments of nasal sprays either as repurposed or antiviral formulations were presented. Nasal vaccines based on traditional medicines, such as grapefruit seed extract, algae‐isolated carrageenan, and Yogurt‐fermenting Lactobacillus, are promising and under active investigations. Inherent challenges that hinder effective intranasal delivery were discussed in detail, which included nasal device issues and human nose physiological complexities. We examined factors related to nasal spray administration, including the nasal angiotensin I converting enzyme 2 (ACE2) locations as the delivery target, nasal devices, medication translocation after application, delivery methods, safety issues, and other nasal delivery options. The effects of human factors on nasal spray efficacy, such as nasal physiology, disease‐induced physiological modifications, intersubject variability, and mucociliary clearance, were also examined. Finally, the potential impact of nasal vaccines on COVID‐19 management in the developing world was discussed. It is concluded that effective delivery of nasal sprays to ACE2‐rich regions is urgently needed, especially in the context that new variants may become unresponsive to current vaccines and more refractory to existing therapies.