I would say way more than 8 million have had it...probably more like 80 million...so dividing the total population by just the reported cases is not accurate at all for any meaningful statiistics.
Let's assume that's true. We'll see if the most optimistic projections for the pro herd crowd make a Lets Go Herd strategy make sense.
80 million cases is nearly 25 percent of the country. Which is still nowhere near herd immunity. Estimates for herd immunity range between 70 and 90 percent of the population- at 70 percent, you see a reduction in case transmission, and at 90 you see near immunity with some sporadic cases. If 80 million people had been infected, and about 250 milliom had not, then over 75 percent of the country will not have had it yet. The odds of you getting someone else sick have not gone down significantly enough to slow transmission, let alone stop it.
Let's also assume the most optimistic case that people who have been sick can't get it again. That is currently in doubt. If people can get sick again, then herd immunity simply doesn't exist without a cure or effective vaccine. For the sake of argument, we'll assume you can't get covid twice.
Next, who are the 80 million people who have gotten sick, and who are the 250 million uninfected? Let's take the US population and measure them on two things- most likely to get infected, and most at-risk. If we split those up, we'll see that the people who are most at risk are usually also least likely to get infected, because they are taking every precaution right now. And the people who are most likely to get infected are the people who were least at risk, because healthy 25 year olds are less likely to have stayed quarantined since March. Not all of the high likelihood people have been infected, but a lot more than the low likelihood crowd.
The least likely to be infected, on the other hand, are the people in rural areas with few cases, people who have been working from home and taking maximum precautions, and people who have no choice but to take precautions because they or a loved one are severely immunocompromised.
In other words, there are some people who are at high risk and havent been taking precautions, and low risk who have been taking precautions, but mostly you will see that the highest risk people have been taking the most precautions and the lowest risk people the fewest.
If 80 million people have been sick, but only 8 million know it, then 72 million people have been sick and don't know it. That's great, right? Because those people might not be able to get it again!
Except that there are over 300 million people in the US, and we don't know which 72 million have been sick. If we could find out exactly which people were immune, then we could open things up for them. But we don't know that. So all the moderate risk people are out walking around, getting each other sick, and continuing to spread this virus towards the goal of herd immunity.
Unfortunately, that means that the death rates will likely go up. Because the highest risk people haven't been going out, and they are now more likely to die or get seriously ill.
Meanwhile, the most reckless people are less likely to wear masks to protect them, because individually, they see themselves as very low risk - they might already have had this, and even if they haven't, they're young and healthy and not aware of any preexisting conditions that put them at higher risk.
Do you see why this is a nightmare?