Some of which they know of are:
1. Lowered immunity against variation of the virus
2. Vaccine-associated enhanced respiratory disease. Every vaccine in the past that had this was pulled and the companies license pulled. example: Chiron SARS vaccine of 2004
3. pro-inflammatory which is the worst thing against covid
4. humoral immune responses
5. disrupting sleep cycles
In vitro model for the assessment of human immune responses to subunit RSV vaccines
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7081972/
As one who has had 69 years of respiratory problems, stemming from asthma, allergies, and chronic bronchitis as a teenager and young adult, I'm particularly concerned about the vaccines' potential for making my conditions worse. (I also have hypertension and peripheral neuropathy but those don't seem to be major contraindications for the vaccine.)
"Vaccine-associated enhanced respiratory disease" sounds like exactly the kind of thing I very much do NOT want to run into.