I don’t think I can get it down to kindergartner level, but I’ll shoot for 5th or 6th grade level. Then you can ask me specific questions about things that still don’t make sense.
So, the first thing is that your immune system is very complex. Most often people equate antibodies https://twitter.com/skp80918488/status/1284460820819111936

with immunity to something, but antibodies are just one part of a very complicated system. Here we go:
1. If a bacteria or virus invades your body, and you have never been exposed to that invader before, the first response of you body is to send in ground troops that will try to

stop these invaders at your border (skin and just under your skin if you get cut; or your nose and throat if it is trying to invade your body there; or your gut, if it is trying to invade your body there). The ground troops with their rifles are called white cells and they don’t

care who the enemy is, they just attack and try to shoot anyone (in this case a bacteria or virus) who doesn’t have their same uniform (in this case features these white cells recognize as being your own body parts). Just like we have different forces (Army, Marines, Navy, Air

Force, National Guard, etc.) and they all have slightly different roles, we have many types of white cells in our blood, & they each do different kinds of warfare against these viruses and bacteria.
2. Just like our initial ground troops can throw a hand grenade or fire a cannon

shot and these blow things up, but rather indiscriminately, our white cells start releasing chemical warfare against these invaders of our bodies and they cause some indiscriminate inflammation but as an attempt to slow these invaders down. What our ground troops (white cells)

are trying to do is prevent these invaders, in the case of viruses, from crossing that border (our nasal passages and throat) and entering into our towns (in this case our cells) where they can take over our food supplies and manufacturing plants where they can make more invaders

(viruses) that can then increase their attack on us. 3. This chemical attack is what makes us feel bad - fever, aches, cough, runny nose, etc. 4. Now, all this time that our ground troops (white cells) are fighting them off at our borders with their rifles, hand grenades and

cannons, they have already sent the message back to headquarters that we have invaders, this is what they look like and now we need some weapons that will specifically target these invaders to stop them before they get into our town and cities (cells) because often with our

rifles, grenades and cannon balls we are killing some invaders, but sometimes we have soldiers who die of friendly fire, plus we are blowing up our own buidlings, so we need HQ to make a new weapon that will hone in on an enemy and kill it and not destroy everything around it,

which in this case happens to be our own cells and tissues. So the troops send HQ a body part of an invader that they killed. HQ then sets up the manufacturing plant and makes a specific-targeted bomb that recognizes something that is different about these invaders from our own

white cells and other cells. This different thing is called an antigen and HQ manufactures these special bombs that only blow anything with that antigen and leaves everything else alone. These bombs are called antibodies and it ordinarily takes us 7-14 days to make them. In the

meantime, our ground troops have to hold off the invaders. Sometimes they do, but often time some of invaders get into our towns take over our food supply and manufacturing plants and make more invaders.
5. Now if you get an antibody test while you are sick, but before before HQ

has had a chance to make antibodies, the test will be negative, even though you are infected. That is called a false negative. It is also possible that you had some left over antibodies from a prior invader who looks a lot like this invader, but you already won that war, but the

antibody test says oh yes, you have antibodies to this new invader, because the bombs look a lot alike but the bombs actually don’t work on this new invader or don’t work very well. That is called a false positive - it is telling you that you have antibodies when it is not the

ones we were really looking for. Unfortunately, that can make someone think they are protected, so they can just hang out with the invaders in close contact, when they aren’t protected and now they have just gotten close enough to someone with the invaders that the invaders are

now at your border. 6. Now, these bombs (antibodies) come in all kinds. Antibodies often do win the war, but they don’t always. We have examples of other virus invaders where HQ manufactures plenty of antibodies, but the invaders march on and take over our cities and don’t seem

to be slowed down by the antibodies. In the case of this Coronavirus, we think antibodies are important, but we don’t know yet. (Another reason you save your money and don’t get an antibody test). Now, back to the types of bombs (antibodies). It turns out you need one kind of

antibody if the invader is crossing the skin or nose border (IgG) and another type of the invader is trying to cross the gut border (IgA). Polio was a gut invader. We developed two different vaccines- a shot and a sugar cube and the sugar cube worked the best because it caused HQ

to make IgA better than the shot did. The Coronavirus does attack both the nose and gut borders. Everyone talks about IgG, but we don’t know if IgA is important. The good news is that I am hearing that at least one of the vaccines seems to stimulate both responses. 6. Okay, back

the types of bombs HQ is making. In addition to different types of antibodies like IgG and IgA (and there are others, but we will save that for middle school) some of these bombs are really potent killer bombs called neutralizing antibodies, because in a test tube they keep the

enemy from entering our towns and cities (cells) and if the invaders can’t get into our cells they can’t make more invaders, so, when we shoot or bomb all of the invaders at our borders, its over because that is all the invaders there are. Recent studies have been disappointing

here. Of those who have been infected, it appears that only 1-10% of people make these neutralizing antibodies in levels that based on other infections, we would guess that these would be clearly effective. Now, let me say that we don’t know whether they work in humans (just

because they work in the test tube, it doesn’t doesn’t mean they work in bodies) and we don’t know if they important in the immune response to this Coronavirus (there are a few other viruses that people make tons of neutralizing antibodies to, but the infection matches on). Now,

if not everyone is making neutralizing antibodies or enough neutralizing antibodies, what are they making? Well, some of these other bombs (antibodies) are like paint balls, where you shoot the invader and it doesn’t kill them, but they are marked. (Continued in next thread).