Vaccinated US health experts are wearing masks indoors as the Delta variant spreads

• The CDC says if you're fully vaccinated, you do not need to wear your mask indoors in public.
• But many leading health experts are still being cautious, masking around others when they don't know their status.
• Vaccines still work well against severe cases of the Delta variant, but many experts say "why take the risk" of even a mild case?

It's been seven weeks since the CDC announced that fully vaccinated Americans can feel safe going about maskless pretty much anywhere they want.

But some health experts are still hesitant to go totally maskless, especially in public indoors.

"Better safe than sorry" seems to be their mantra as the more contagious Delta variant becomes dominant.

'Why take the risk?'

Professor Don Milton from the University of Maryland, a leading expert on airborne viruses, told Insider he still wears a "tight fitting" N95 mask at the grocery store. He goes mask-less when working indoors at his lab, where the rooms are well ventilated and "everyone has been fully vaccinated with mRNA vaccines."

Though 70% of adults in his state have received one dose of a vaccine, Milton's still concerned that "lots of areas of my county are below 50%, and my zip code is at about 60%."

"I realize I'm not likely to die if infected - but I'm in a high risk group," he said. "I could still get ill, miss work, screw up my vacation, and [there's] a small risk that I'd have long-term effects. Why take the risk?"

Milton is not the only one being cautious. Dr. Megan Ranney, a professor of emergency medicine at Brown University, employs a similar strategy.

"I still generally wear a mask indoors if I'm in a public space," Ranney said.

She's not changing her habits based on the spread of the Delta variant but she will monitor the local infection rates in Rhode Island, where 67.4% of adults are fully vaccinated.

"If I'm with friends or colleagues who I know are fully vaccinated, I never mask," she said. "Our vaccination rates are high and our infection rates or low, so I feel comfortable being a little looser with my precautions, given that I am fully vaccinated."

Vaccines work against Delta

The CDC maintains that fully vaccinated people don't need to wear masks indoors anymore, despite the rise of the more transmissible Delta variant in the US.

In the UK - where Delta reigns - studies suggest infections are rare for vaccinated individuals, and when they happen, they're mild.

One recent study in The Lancet found Pfizer's vaccine reduced the risk of symptomatic cases of the Delta variant in Scotland by 79%. Another from Public Health England suggested Pfizer's two-dose vaccine is 96% effective at preventing hospitalizations.

When vaccinated people do become infected with Delta, their symptoms tend to be more cold-like - a headache, a runny nose - and almost never require hospitalization.

Not everyone has the kind of vaccine access the UK and US do, though. Only 11% of people worldwide are fully vaccinated, and not all the vaccines work equally well.

So, the WHO still suggests that even fully vaccinated people should continue to mask in areas with higher rates.

"Vaccine alone won't stop the community transmission," the WHO's Dr Mariângela Simão said during a recent WHO press conference. "People cannot feel safe just because they had the two doses. They still need to protect themselves."

In Los Angeles, where the Delta variant makes up half of all sequenced coronavirus cases, the health department "strongly recommends everyone, regardless of vaccination status, wear masks indoors in public places as a precautionary measure."

Dr. Monica Gandhi, an infectious disease expert at the University of California, San Francisco, thinks the hype over Delta is unscientific.

Because data suggests all the vaccines authorized in the US are still highly effective, the only time she wears her mask indoors is when it's required.

"I am still comfortable with that position despite the Delta variant," she said.