Pathogens can produce allergens!

Allergic reactions of pathogens cause problems. For example, Yeast as a "pathogen" releases "Toxins" into
host cells. The toxins are indirect effect of pathogen
Yeast building up in our bodies, once their level reaches certain limit as endured by body for its functions.

Vaccinia viruses are processed in laboratory taking all these aspects into consideration for all people.They are made less potent or less virulent than those that would normally occur in wilderness or in our free envt.

If a child/person/organism develops a certain reaction from any injected med or ingested food, it is because the body is reacting to it. The food or med is not compatible to the genes that can handle them. But to customize each and every person's med and food using each individual person's genome is a long way to go!
People just freak out if you mention the word genes!
Forget about genomic proteomic customized medicine and vaccine for the entire world population. It is not practical or possible in our times now.

Also, we have to know which child or person has pre-existing genetic flaws. Or gentic aberrations way before hand in order to customize something so specific for each individual body and mind!

The type of reaction developed is determined by the functional capabilities of those particular genes (MHC) that process these particular stimuli. IF THE GENES ARE MALFUNCTIONING FOR SOME KNOWN OR UNKNOWN REASONS, THEY WILL NOT PROCESS ANYTHING RIGHT.

So the bottom line is GENES! Check them out today.