My understanding (I could be wrong) is that a person who has been vaccinated can contract and then carry the virus for a short period of time and infect a non vaccinated person during that small window of time.
This is what they are telling us, but it is a guess not a fact. And this is the problem. The experts are doing a lot of guessing when they do not know the answer. Remember when they told us that immunity did not last long or that there was no immunity for people who had recovered from COVID. Now studies show that a year after infection, over 99.7% of recovered patients are still immune to reinfection. The "experts" believe immunity lasts much longer than originally expected.
Think of how the vaccines work. They attack the protein that the spikes on the virus are made of. This prevents the virus from entering cells to reproduce. If the vaccine works, then a vaccinated person who comes into contact with the virus will never have more of the virus than what he originally contracted and the amount of virus will diminish as the virus dies off. To transmit the virus to another person, the infected person has to be shedding a certain quantity of the virus, not just a single virus particle. So transmission from a vaccinated person is highly unlikely. Additionally, the vaccinated person, even if he is carrying the virus, will be asymptomatic and we have also discovered that these people are less likely to spread the virus.
And again, even if a vaccinated person contracts the virus, the only people he can infect are those who choose not to get vaccinated, which is their choice and the risk they take.
People need to remember that these vaccines have been approved only on an emergency basis. They have not been approved under normal circumstance because the testing was shortened to get the vaccines to market. in 1976 the government took similar steps to prevent an outbreak of Swine Flu. 2 1/2 months into a mass vaccination program the program was stopped because 1, that's ONE, person died after getting vaccinated and 5 others were diagnosed with Gillian-Barre Syndrome. That's out of 40 million people vaccinated in the US.
Personally, I think the vaccines are safe and a lot of misinformation has cluttered people's heads. They are focusing on a few individual cases of reactions to the vaccine, ignoring the number of people vaccinated with few severe side effects. However, it is still their choice to get vaccinated or not or to risk illness. If the government can punish us for not getting vaccinated then what else can they force us to do for our own health benefits?