Tests take time. You don’t know what side effects may present themselves one year, two years, five years down the line until you’ve monitored the vaccine for on

Tests take time. You don’t know what side effects may present themselves one year, two years, five years down the line until you’ve monitored the vaccine for one, two, five years. This is one reason vaccines take a long time to test and is why people familiar with vaccines are hesitant to inject themselves with something that hasn’t been tested over a normal period.