Minneapolis mom Sarah Gollust was waiting on her computer at precisely 8 p.m. — the moment when an online retailer replenished supplies of an elusive back-to-school item. But at 8:02 p.m. she got this message: sold out.

Gollust wasn't pursuing coveted backpacks or other cool accessories for her two children, ages 10 and 7. Instead, she was trying to buy "Happy Masks" — colorful, washable face coverings that come in kid sizes and offer upgraded protection against respiratory pathogens like COVID-19.

Gollust, a University of Minnesota public health associate professor, remains on the hunt. The rest of us ought to join her in seeking more effective masks, even if we don't have kids and even if we've been vaccinated. The reason: the highly transmissible delta variant fueling COVID cases across the nation.

The resurgent virus caused the U.S. Centers for Disease Control and Prevention to update guidance and recommend universal masking for teachers and students ages 2 and up in K-12 schools. Masking indoors — even for those immunized against COVID — is also advised elsewhere in areas with high or substantial viral transmission. As of Friday, that included all but a handful of Minnesota's 87 counties.

If we need to wear masks again, it makes sense to don something that offers better protection against infectious particles. High-filtration masks — often referred to by numerical names such as N95, KN95 and KF94 — aren't new technology. But for much of 2020, they were in short supply, with priority for health care workers. Those not on the front lines relied on cloth or paper masks.

Fortunately, high-filtration masks have become widely available for adults as COVID's threat ramps up. Suppliers are also pushing to meet the demand for better face coverings for kids.

Minnesota epidemiologist Michael Osterholm is among the infectious disease experts advocating a move to more effective masks. This advocacy, particularly his remarks during a recent CNN interview, has sometimes been misinterpreted to mean that masks are ineffective. Outspoken sports and political commentator Clay Travis tweeted in response: "As I've been saying, this is all just cosmetic theater."

But in an interview with an editorial writer, Osterholm said his point was that better masks are now widely available and that it makes sense to switch due to delta's risk. He's been wearing an N95 mask and recommended buying from trusted suppliers such as Grainger.com. That said, Osterholm still recommends wearing a cloth mask if nothing else is available, as well as continuing to social distance no matter what mask you have.

A quick shorthand for those sorting through N95, KN95 and KF94 terminology: The numbers refer to the percentage of tiny particles the mask captures. The letters refer to the country whose regulatory standards the mask meets. The "N" in N95s refers to the United States. KN equals China, and KF is South Korea.

A new tip sheet from Eva Enns, a U School of Health associate professor and mom of two, is aimed at helping parents choose a mask for their kids, but the advice is applicable to all ages. Among other things, it outlines how to get a good fit and how to avoid counterfeit masks when searching online retailers.

High-filtration masks can be more costly. The Happy Mask "Merry Mermaids Pro" model runs $24. It's reusable, but the price tag may be daunting. Minnesota schools should buy these masks in bulk at a discount and provide more effective masks to all students.