With a potential eighth wave of the pandemic sweeping across Australia, an analysis of US data from the pandemic has reiterated that observational studies have demonstrated the effectiveness of masks in preventing the transmission of SARS-CoV-2 on airplanes, in schools, and among household and community contacts of individuals with COVID.
The research, published 1 November in JAMA Open Network, highlighted that a COVID outbreak on the aircraft carrier the USS Theodore Roosevelt was particularly instructive as it occurred early in the pandemic before crew members would have had any immunity to SARS-CoV-2.
“Ships are high-risk environments for respiratory disease outbreaks because they bring people together for prolonged periods in often poorly ventilated close quarters,” the authors said.
“More than 80% of those who reported not masking were infected, while the odds of infection were 30% lower among those on the ship who reported masking.”
Similarly, in Germany, an opportunity to generate high-quality data arose when different regions mandated masking at different times during the pandemic and mask mandates were associated with a 45% reduction in infections.
However, the analysis also noted that the risk-benefit calculations that shaped public health recommendations could differ by setting and may be subsequent to change over time, and that their effectiveness was dependent on many factors.
“No public health intervention, even a highly efficacious vaccine, is 100% effective. Even the best masks will not provide complete protection, and benefits of masking are limited if masks are not worn everywhere transmission occurs,” the authors said.
“In any pandemic or epidemic, masking will be just one of a series of interventions.”
The most effective strategies to limit illness and death from SARS-CoV-2 and other respiratory pathogens involved a layered response, including vaccination when available, isolation of infectious people, and protection through risk reduction—including the use of high-quality masks by vulnerable populations in areas and at times when the pathogen was spreading.
The analysis also pointed out that there was abundant evidence that school closures were deleterious to children’s health and that masking in schools decreased transmission of COVID within classrooms.
“Using measures including masking to protect high-risk people in the school community and to keep schools open is likely to result in better health and educational outcomes than school closures,” the authors said.
“Consideration of trade-offs should inform future decisions about masking in schools to prevent the spread of respiratory viruses, and frequent reassessments of the epidemiologic context and available evidence can help maximize benefits and reduce disruption and potential harms.”
Although other concerns raised about masks included possible impacts on respiratory function, this factor was dismissed as insignificant in the analysis’s findings.
“Although masking can be uncomfortable, especially in warm conditions, there is no compelling evidence of consequential deleterious effects on physiology, including during exercise,” the authors concluded.
How long should kids isolate after they’ve contracted COVID?
Another US study, also published this week on JAMA (Paediatrics), demonstrated that children infected with the Omicron variant remained infectious for a median time of three days after testing positive for the virus.
The team from the University of Southern California concluded that school policies that require students with COVID to stay out of the classroom for five days were more than sufficient and that public-health and education leaders could even consider implementing shorter durations.
Co-author Dr Neeraj Sood, Director of the COVID Initiative and a senior fellow at the USC Schaeffer Centre, explained that the study showed the median time of infectivity was three days, with 18.4% of children still infectious on day five and 3.9% infectious on day 10.
“We also found no association between how long children were infectious and whether they were vaccinated, suggesting return-to-school policies may not need to discriminate by vaccine or booster status,” Dr Sood said.
“We want to protect the other children in the school who could potentially get infected, but at the same time, we don’t want to disrupt education for the child who is infected, given the amount of disruption that’s already happened.
“The duration of infectivity is an important parameter into figuring out what the optimal duration of self-isolation should be.”
The researchers examined nasal swabs from 76 COVID-infected children between the ages of 7 and 18, who tested positive for the Omicron variant, over 10 days with samples examined daily to find evidence of cell death, a sign of infectivity.
The findings were consistent with previous research on adults who contracted the Omicron variant, which showed no association between vaccination status and time of infectivity, and Dr Sood has called for further research so that policymakers could consider adjusting the recommended time for students to stay out of the classroom.
“The virus will keep mutating,” Dr Sood said. “We need to continue doing studies like this because the next variant may have a longer or shorter duration of infectivity.”