Several mRNA vaccines are used on the population in the U.S. My prior simulation study and model study enabled me to identify many flaws in clinical trials, side-effect evaluation methods and mechanism studies. Persons have organs’ functional reserves, which could be from a few percents to many times of the minimum functions necessary for sustaining life. It is an indisputable fact that drugs and chemicals can slowly damage cells and tissues without causing any symptoms. To find a better approach to assessing vaccine risks, I consider failure in predicting drug side effects in product liabilities and removals of FDA approved drugs. Based on evidence I have found, I conclude that the risks of vaccination cannot be determined by experiments alone and must be determined by using a combination of methods. By studying mRNA expression dynamics and kinetics, I predict that vaccination with mRNA vaccines may increase cancer risks by affecting the Central Nervous System, interfere with normal protein synthesis, dramatically disrupt the normal immune system, alter the normal selection process for viral evolution resulting in more virulent viruses, and aggravate chronic diseases or cause them to relapse. Two root problems are practical inability to control expression sites, and expected severe adverse reactions from repeated vaccination, particularly, booster shots. Off-target expressions may result in unknown health effects while the severe adverse reactions pose unreasonable risks on persons whose vascular functional reserves are relatively small, or whose vascular systems are temporarily burdened by other causes such as viral infections or life activities. If an mRNA vaccine is administered on a pregnant women by second or booster shots, spike protein synthesis in fetus brain disrupts the highly regulated protein synthesis processes, resulting in potential brain damages. I found that the actual number of deaths caused by mRNA vaccines has been grossly underestimated.