In May, things were looking good — or at least better — thanks to dropping COVID-19 case counts and powerful vaccines. The Centers for Disease Control and Prevention (CDC) said that most people who were fully vaccinated against COVID-19 needn’t wear masks indoors in public.

States and counties across the country eagerly began dropping their mask mandates.

Lt. Gov. Josh Green told Hawaii News Now he thought that Hawaii’s mask mandate should be lifted for vaccinated people indoors.

“I would prefer that we lift the mask mandate indoors if you are vaccinated,” Green said. “I think it’s about time.”

Not anymore.

This week, in an alarming reversal, the CDC recommended that people in substantial- or high-transmission communities — vaccinated or not — put their masks on when indoors in public spaces. This would include Hawaii, which the CDC says has a substantial rate of community transmission.

The latest data suggest that the delta variant can infect even vaccinated people, who could harbor large concentrations of the virus and perhaps spread it to the most vulnerable, including children under age 12 who can’t get the vaccine. And while vaccinated people still appear much better equipped to resist the effects of the virus, the CDC’s reversal illustrates the dangers of complacency and premature assumptions.

At this point, no one really knows where the COVID-19 pandemic is going, or how it will end. Right now, it looks as dangerous as ever, if not more so.

But thanks to the hard-won lessons of the past year, we do know how to slow it down: getting vaccinated, or course, but also the old standbys of washing hands, social distancing and crucially, wearing masks.

Gov. David Ige had eased the state’s outdoors masking rules, but — presciently, as it turned out — refused to budge on the mandate requiring masks indoors.

“I’m really happy that in our state, we really didn’t let our guard down,” said state Health Director Dr. Libby Char, talking on the Star-Advertiser’s Spotlight program Friday.

Indeed. Unlike many places on the mainland, Hawaii residents by and large have accepted the need to wear masks indoors. And the state’s mandate keeps things simple and relieves businesses of the burden of justifying the rule to recalcitrant customers.

Still, the brief spark of hope last spring muddled the message. The state should ramp up public awareness campaigns, targeting the biggest source of new infections: local residents who may have let their guard down. Those with at-risk loved ones at home should consider double-masking, if possible.

Right now, we need to return to these familiar safety measures. Otherwise we risk returning to other ones, such as stay-at-home orders and shuttered businesses. Mask up.