First and foremost, not all bodies are created equal. Someone may have stronger immunity while others had weaker one. There is no evidence that proves an unvaccinated will cause any harm to anyone else. If someone is vaccinated and if the vaccine is scientifically proven to protect then that person should have no fear being around an unvaccinated person.  There is also evidence from studies conducted by the CDC that demonstrates vaccines aren’t fully protective and can actually cause someone to acquire other forms of respiratory illness  

secondly, every body is unique and each person may or may not experience adverse reactions from a medical intervention. As there are risks associated with the vaccines, it should be the person or their parent to decide whether they should take the risk or not. No person has more right to live than another and every life is equally precious. We have the right to choose whether we want to risk personal injury from a medical intervention such as from a vaccine or not. Forcing mandatory vaccine is like forcing Russian roulette on someone’s life.  

Additionally, not all infectious disease are spread in school environment.  Some such as Hepatitis is spread through intercourse or spread of bodily fluids, tetanus cannot spread via the environment, and many others.  

https://physiciansforinformedconsent.org/influenza-flu-vaccine/