Absolutely, one great paper that summarizes many of the studies is the Cochrane review. They are an independent scientific body focussed on evidence based medicine. You can read the Cochrane review article on sublingual immunotherapy here:
That number is from the line "SLIT-induced anaphylaxis equate to around one case per 1000 million SLIT administrations or per 526,000 treatment years'.
https://pubmed.ncbi.nlm.nih.gov/21154351/
Another paper discussing the safety of sublingual immunotherapy can be found here:
Sublingual allergen immunotherapy: mode of action and its relationship with the safety profile https://pubmed.ncbi.nlm.nih.gov/22150126/
That number is from the line "SLIT-induced anaphylaxis equate to around one case per 1000 million SLIT administrations or per 526,000 treatment years'.
Another nice review paper can be found here:
https://pubmed.ncbi.nlm.nih.gov/28964530/
Hope this helps!
Manan