Wearing a mask would be a good idea.

Getting a COVID-19 vaccination would be a better one if you haven’t already had a shot.

But for now, even people who are vaccinated should start wearing masks again when going in stores and other places with lots of people.

Lord knows no one wants to go back to that again, but it’s necessary. More on the reason for that in a moment.

But first, no one should say the Centers for Disease Control and Prevention “reversed course” on its guidance for masking. Two things happened:

1. The CDC said in the spring that vaccinated people could stop wearing masks because the vaccines were highly effective against both transmission and severe infection of COVID-19, but what followed was that everyone in the country stopped wearing masks or taking any precautions whatsoever.

2. Then the delta variant came.

These things in combination are why masks are necessary again.

The delta variant of COVID-19 is spreading like wildfire. It’s not just twice as infectious as the alpha variant, which is the one that caused so much severe illness and deaths at the start of 2021, it is many times more infectious — as infectious as the chickenpox, health officials said late last week.

The reason it is so much more infectious is it reproduces faster, so an infected person sheds a great deal more of it and starts doing that within a few days of infection. The air that that person exhales is virtually swimming with virus.

Because almost no one is wearing masks anymore, and because people largely are not observing distancing, that means a lot more virus is in the air and reaching a lot more people.

Even with the alpha variant, scientists never said that the vaccines would prevent infection 100% of the time but that they had proven they would almost always keep you from getting seriously ill, and they appeared to make you unable to transmit the virus.

The delta variant is different. It may be better able to infect vaccinated people.

Importantly, the vaccines still have been effective in preventing those people from getting seriously ill — officials at hospitals in places like Florida and Missouri that are being overwhelmed with COVID-19 patients say that 99% of those patients are unvaccinated.

But it also appears that vaccinated people may be able to transmit the delta variant to others.

The delta variant also appears to be more likely to make younger people become seriously ill. Pediatric wards in hard-hit areas are seeing more children than ever with severe COVID-19 symptoms.

The COVID-19 that is circulating now is not the same as the kind circulating in January. It is much more serious and much easier to catch.

If we don’t all do what we can to reduce its opportunity to spread, this summer and fall are going to be hell for the health care system and anyone who might need help — not just COVID-19 patients. Anyone suffering a heart attack, a stroke, a broken leg from a car wreck, a dog bite, a burn injury.

When the hospitals fill up, the ripple effects rock everyone’s boat.

Wearing a mask is an almost effortless way to keep those ripples from becoming waves. If you don’t breath it in, you can’t catch it, and if the mask keeps it out of the air around you, you can’t spread it to others.