Masks Can Limit Household Spread Before Virus Symptoms Appear

(Bloomberg) -- Face masks can help keep the coronavirus from spreading within households -- but only if they go on before symptoms appear, according to a study.

Masks were 79% effective at halting spread of the virus if at least one person in the home started wearing a face covering before anyone got sick, according to a survey of 124 families in Beijing published in BMJ Global Health. Using disinfectant every day, opening the windows and staying at least 1 meter apart were also linked with lower infection risk.

The results support the idea that universal mask use could help keep people who don’t know they’re infected from spreading the virus, the authors wrote. Families with members at high risk for transmission, such as medical workers, might consider wearing masks too, they said.

The families questioned in the survey included 460 people, with higher-risk grandparents frequently under the same roof as children and grandchildren. Each family had at least one confirmed Covid-19 case between late February and late March. The survey also showed that spread within households is by no means guaranteed. About one in four of patients’ family members were infected, with such secondary transmission happening in about one-third of the families surveyed.

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