I don't know why it takes so much longer to develop nasal-spray vaccines. Cuba has been working on its own, Mambisa, for as long as on its other vaccines, Abdala and the three Soberanas:
Cuba’s bet on home-grown COVID vaccines is paying off (Nature, Nov 22, 2021)
Mambisa from Cuba could cut transmission of the coronavirus (BMJ, Jan 27, 2022)
Avanzan ensayos clínicos de candidato vacunal Mambisa de Cuba (Radio Habana Cuba, Jan 23, 2022)
In all groups, he added, the vaccine candidate induced an anti-RBD response by more than four times the initial level.
It also increased the inhibitory capacity against the SARS-CoV-2 coronavirus, which causes Covid-19, more than 20 percent, at the systemic level and in the nasal mucosa.
Mambisa is a combination of two recombinant proteins: the RBD of the SARS-CoV-2 spike and the nucleocapsid of the hepatitis B virus.
Globally, four other nasally administered candidates have reached the stage of clinical studies, according to recent public data.
Cuban nasal vaccine against Covid-19 stands out in El Salvador (Prensa Latina, April 18, 2022)
]San Salvador, Apr 18 (Prensa Latina) The development in Cuba of Mambisa, a nasal vaccine to strengthen immunity against Covid-19, is highlighted today by Salvadoran media.
“Cuba is about to launch an anticovid vaccine that is administered through the nose,” headlines newspaper El Mundo, which highlights the progress in clinical trials of the new vaccine candidate from the Center for Genetic Engineering and Biotechnology (CIGB).
The aforementioned newspaper reproduced the “tweet” of the CIGB on the positive results that support the use of Mambisa in the application of booster doses.
Finland has also been working on a nasal spray against the virus. It sounds good ... until you get to the "up to 8 hours"
New nasal spray effective against all variants (National Herald, Jan 12, 2022)
The nasal spray consists of a molecule, developed by researchers at the University of Helsinki, Finland, that can inactivate the coronavirus spike protein
Finnish researchers have developed a novel nasal spray that is effective against all variants of Covid and can prevent infection up to 8 hours.
But on the other hand, consider this:
In contrast to vaccine protection, the effect of TriSb92 begins immediately after its administration.
I wouldn't mind having a whiff of it immediately before boarding a plane, for instance. I have recently read a couple of stories about people on planes coming down with Covid-19 after sitting next to passengers who were coughing and sneezing, unmasked.