[superkuh]

Yes. No intramuscular vaccination for a respiratory virus is going to be effective at preventing infection of the surface, mucosal, tissues in the upper respiratory tract. The IgG antibodies in the body serum do seep into the lower lungs though and prevent serious diseases there and in the body proper.

To provide sterilizing immunity to the upper respiratory mucosa we'll need an intranasal booster after the intramuscular to recruit resident B and T cells to the upper respiratory mucosa. There the B cells will make IgA antibodies for a much longer time than IgG antibodies can seep in at any useful level. Additionally the resident T cells will kill off any cells that do get infected.

This is a nuanced issue. We need to be clear that there is a difference between infection of the body organs and infection of the surface mucosal tissues.

ref: https://science.sciencemag.org/content/373/6553/397

ref: https://www.gov.uk/government/publications/long-term-evoluti... page 5, #8. "Whilst we feel that current vaccines are excellent for reducing the risk of hospital admission and disease, we propose that research be focused on vaccines that also induce high and durable levels of mucosal immunity in order to reduce infection of and transmission from vaccinated individuals. This could also reduce the possibility of variant selection in vaccinated individuals."

ref: https://www.nature.com/articles/s41577-021-00550-x

[l33tman]

But won't the mucosa learn to produce the IgA antibodies when you get exposed the next time though? The virus is going to be endemic forever, all who got and will get the vaccine are going to get exposed again and again.

In other words, for the already vaccinated (or post-infected) won't repeated exposure also act as a booster?

[superkuh]

Sure. But that means you're spreading the virus, you're taking a small serious health risk, and you're giving the virus tissues in which it can fall back to while simultaneously mutating under IgG antibody pressure in the lower lungs. That keeps the pandemic going.