Hard to say what the first shot actually gives you. Like I said a day or so ago, not much data was acquired on first vs second dose since multiple dosing regimen, durability and follow up wasn’t done. Just guessing based on other vaccine research, the first dose is probably pretty effective, at least in the shorter term (think months). The second one is important to cement the memory aspect. But 80% is what Ive seen for the first one. But the durability is probably not as good without the second dose.
If your going to get the first one, not getting the second one is foolish.