It's been a quiet week in politics. The type of quiet week that used to regularly happen when Congress was off on yet another of their multi-week holidays and not much was happening at the White House. Perhaps this August we'll even return to a real "silly season," where all the political reporters and pundits feverishly look for something interesting to write about. But after four solid years of a never-ending silly season ("insane season" would be more accurate), it's kind of quaint and normative to enjoy a week like this again, I must say.

President Joe Biden did give a short speech today on his vaccination effort. He had to admit that for the first time he had fallen short of one of his own self-imposed goals. America has not reached the mark of having 70 percent of all adults at least partially vaccinated, but we did at least get north of 67 percent by Biden's Independence Day deadline, which is pretty close.

Biden talked today about the efforts his team will be making from now on to reach the hard-to-get people who have not yet gotten their free vaccine shots. And he's got an uphill climb among certain slices of the population. But what I've been wondering from the start is how America will achieve the "herd immunity" level where the virus begins to just die out for want of unprotected victims. Note I said "how" there, not "if." We will get to herd immunity eventually, but it's looking like the last stretch might have to be done the hard way instead of the easy way. More on that in a moment.

First, let's take a look at the numbers. As of today, 182.7 million Americans have received at least one dose of the available vaccines. A total of 157.6 million have been fully vaccinated. This is out of an overall population of 332 million, which means 55.0 percent of the country has been partially vaccinated while 47.5 percent has been fully vaccinated.

These numbers may sound low, but that is because there are at least three separate ways to measure the relative success of the vaccination program. Measuring against the total population (all those numbers, above) is the toughest way to do this, but it is also the one that is most important when talking about herd immunity.

The other two ways to measure are to take only the subset of "all adults" (everyone 18 years old or older) or the larger subset of "all who are eligible" (everyone 12 and up). Right now, 67.2 percent of all adults have gotten at least one dose. This sounds a lot better, since it is over 12 points better than the "total Americans" measure -- which is probably why Biden chose it as his metric to target (even if he missed his 70 percent goal).

But herd immunity is really only going to be achieved when the lower "all Americans" percentage moves above 70 percent. The virus doesn't care what age you are, to put it another way. Kids may not get hit as hard by it, but they can still catch it and spread it, so they have to be included.

There is no hard-and-fast agreed-upon percentage for herd immunity, either. Some experts put it as low as 70 percent, some put it as high as 85 percent. But we'll really only be within reach of achieving it when the entire country hits at least 70 percent, so that's a good enough target to shoot for at this point.

This means we've still got at least 15 percent more of the public to go. That's a lot, and the rate of new vaccinations has slowed to an absolute crawl. Just taking the currently-eligible population into account, it may prove to be impossible to even top 60 percent at the rate we've been going. The remaining unvaccinated population is getting harder and harder to reach, which is why today Biden touted what will come next (getting the vaccine to local doctors, going door-to-door with shots, mobile vaccination vans, etc.). Biden's team is trying to reach every person who can be persuaded, in other words. But there are a whole bunch of people who are just never going to be persuaded. And politics is at the heart of this. Here are some stunning statistics from a recent Washington Post-ABC News poll: "86 percent of Democrats have gotten at least one vaccine shot, compared with only 45 percent of Republicans. Forty-seven percent of Republicans say they likely won't get vaccinated, compared with only 6 percent of Democrats." This partisan divide is just not going to go away, not at this point.

But there's one thing which will help enormously. Trials are happening right now so that the vaccines can ultimately be approved for everyone below the age of 12. Sooner or later, one of the vaccines will get emergency authorization, and the youngest Americans can start getting their shots. And there are a a lot of them -- 52 million, in fact. That right there is over 15 percent of the country's population.

Of course, not every kid will get vaccinated. Some parents won't allow it. But schools requiring vaccinations will spur the effort to get as many of them protected as possible. So a goodly portion of them will get vaccinated, and it will probably come as a giant wave once the authorization is granted. So in a very short time, the overall numbers and percentages for the country as a whole will shoot up.

If we can get to somewhere in the close neighborhood of 60 percent of all Americans vaccinated before this wave hits, then it's not unreasonable to think that at least two-thirds of young children might get their shots soon after. And that would put the nation as a whole right at 70 percent.

That's what to hope for -- that's "the easy way" I mentioned earlier. But we will get to herd immunity even if this goal is not reached -- via the "hard way." Because the measure of immunity in a population does not just solely include those who have been vaccinated, it also includes those who have recently contracted and survived the virus. Even people who never had a symptom and don't even realize they caught it. Everyone who has recently gotten sick (say, in the past six months) has produced their own antibodies naturally and are now relatively safe from catching it again even without getting vaccinated (it is still largely unknown how long this "natural immunity" lasts after catching COVID-19). So while the number of vaccinated people might not quite hit 70 percent or above, if you add to it the number of people who have recently been infected and survived, eventually we will achieve herd immunity and the virus will die out for lack of new, still-vulnerable people to infect.

It's a cold equation to even contemplate, though. It essentially means that those who have been vaccinated are going to have to wait around until millions more Americans get the virus, which is going to mean thousands (at the very least) more deaths. All unnecessary and totally-preventable deaths. That's why this truly is "the hard way" to get there.

But that's what we may have to accept, at the very end of the entire vaccination drive. Seeing people needlessly get sick and die just because the followers of one political party have somehow decided that not getting vaccinated is the smart way to go. That is a sad commentary on our country, but it may become an unavoidable one.

Sooner or later America will achieve herd immunity and the virus will become a much more manageable threat. But it's an open question at this point how hard the path to attaining that goal is going to be, and how many more people are going to have to needlessly die before we get there.

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant