Vaccines don't actually protect you against the virus, they just activate your immune system (your body's natural protection). Guess what else also activates the immune system? The actual virus!
At the beginning of the pandemic, there was some talk that anti-bodies might not last longer than 3 months, but that was obviously just FUD (there was literally no data). I had antibodies 6 months after being infected. Two additional things I heard (but don't have the source), your body can restart production of antibodies (B-cells remember), and people had SARS(-CoV-1) antibodies years after infection.
Something can feel instinctively correct and not be correct. For example, the sun going around the earth, or the earth being flat, for that matter.
I'm not saying it should be 0, 1, 2 or 10 shots; I'm saying the answer is absolutely not obvious, even if you instinctively want to say zero.
In a world where we're lacking information, the default should probably be zero. But given that this is a worldwide pandemic, we're not going to be running out of information any time soon, so it's good it's being studied.
It's not FUD. It happens. It might be a small percentage but it's real.
There's a case of someone close to me that works in the ER that was positive around November with very little symptoms, got cured and now has it again but with stronger symptoms.
And from the antibodies tests done to the health personal in that hospital, it seems some people get good antibody response and others not so much.
> Are there any credible studies that say that infection doesn't confer immunity?
Of course! Economic studies said that vaccine manufacturers might not make as much of their investment back if infection confers immunity, so we can conclude that infection doesn't confer immunity.