The vaccines are tested for preventing serious illness, hospitalization, and death. They aren't really tested for preventing catching the virus or transmitting the virus.
Now the question is, if you don't get sick, why do you really care if you catch the virus? Didn't the vaccine work anyway? The answer/FUD being spread about it is that you could potentially still transmit the virus to somebody else who DOES get sick or die, because they are not vaccinated or can't take the vaccine or the vaccine didn't work for them. Which is why the pandemic pushers are so pushy that everyone needs to get the vaccine as soon as possible to save lives, and why even though we have 3 perfectly good and effective vaccines that everyone has access to, we still need to continue the fear mongering about the "pandemic". The goal posts move... first we just need to crush the curve, then we all need to keep up panic because "cases" are increasing as they mathematically inevitably will, now everyone needs to be vaccinated, and the inoculation scare is that we will still have to keep up pandemic measures even for vaccinated people.
The standard for vaccines has always been a macroeopidemiological standard for keeping diseases in control in a population. Everyone knows that vaccines don't always work at 100% and there are breakthroughs and so on. But by the normal standard that doesn't matter because the vaccine is effective if it controls the disease in the population effectively. But COVID has taken on a boogeyman status, and is being considered extra scary and dangerous even though it's actually quite mild, basically a super-flu (if it were some Ebola strain with 40% death rate that makes you bleed out your eyeballs it would be more understandable). So for COVID, the vaxmongers want to apply the standard based on the rare thought experiment that just in case the vaccine doesn't stop virus spread 100%, and just in case someone somewhere might catch it from a vaccinated person, and just in case that person is one of the 0.5% of people who are strongly effected by COVID, because that might happen we need to keep up pandemic controls, but this doesn't mean that we should stop vaccination, on the contrary we need to coerce everyone to get vaccinated, because vaccines are super effective, except they are not super effective enough, so we all need to still be worried. because OMG ThE CoVId!!! I think I got that right.