This story was first published in July 2020
Should there be another outbreak of COVID-19 in New Zealand, don't stock up on toilet paper - vacuum cleaner filters might be a better bet.
New research has found next to medical-grade N99, N95 and surgical masks, vacuum cleaner filters are the next best thing you're likely to have on hand. They're able to decrease the risk of infection with a disease like COVID-19 by up to 83 percent during a 30-second exposure, and 58 percent after 20 minutes.
"We knew that masks work, but we wanted to know how well and compare different materials' effects on health outcomes," said Amanda Wilson, an environmental health sciences doctoral candidate at the University of Arizona.
Unsurprisingly, N99 masks were the best - reducing risk by 94 to 99 percent, even during 20-minute exposures.
"One big component of risk is how long you're exposed," said Wilson.
But they're not always available, and "there are ethical considerations such as leaving those available for medical professionals".
Vacuum cleaner filters can be inserted into filter pockets in cloth masks, Wilson said.
Other possible ad hoc masks that had decent effectiveness included tea towels, cotton-blend fabrics and antimicrobial pillowcases.
"The denser the fibres of a material, the better it is at filtering. That's why higher thread counts lead to higher efficacy. There's just more to block the virus.
"But some masks - such as those made from silk - also have electrostatic properties, which can attract smaller particles and keep them from passing through the mask as well."
Avoid T-shirts and scarves unless there's nothing else around - Wilson saying they fared "only slightly better than wearing no mask at all".
Best defence remains staying at home
While wearing masks can reduce the risk, they're not foolproof - and the research found the longer you wear one, the less effective it becomes.
"Don't go to a bar for four hours and think you're risk-free because you're wearing a mask. Stay home as much as possible, wash your hands often, wear a mask when you're out and don't touch your face."
New Zealand has had no reported cases of community transmission for more than two months now, and life for many of us is largely back to normal. In that time the pandemic has accelerated overseas, with about 250,000 confirmed infections now reported every day - and research suggesting the true figure could be many times that. Many countries and cities remain in various states of lockdown, and will likely be so for months to come.
Part of the seemingly unstoppable spread of the disease is down to people's reluctance to wear masks if they're not personally feeling sick. But the virus behind COVID-19 can be spread asymptomatically - meaning people not even be aware they're infected can still pass it on to others.
"We were focusing on masks protecting the wearer, but they're most important to protect others around you if you're infected," said Wilson.
"If you put less virus out into the air, you're creating a less contaminated environment around you. As our model shows, the amount of infectious virus you're exposed to has a big impact on your infection risk and the potential for others' masks to protect them as well."
Wilson's research was published in the Journal of Hospital Infection.
