Wearing face masks at home could help to stop the spread of Covid-19 among people in the same household, but only before symptoms develop, according to a Chinese study.
Questioning Chinese families in Beijing found that it was 79% effective at curbing transmission before anyone in the household developed symptoms. However, it offered no protective effect once symptoms had developed.
Figures in China suggest that most person-to-person transmission of SARS-CoV-2 occurred in families, so to explore if face masks could make a difference researchers questioned 460 people from 124 families in Beijing, on their household hygiene and behaviours during the pandemic.
Each family, which comprised an average of four people but ranged from two to nine, had at least one laboratory confirmed case of Covid-19 infection between late February and late March 2020, and they had lived with the infected person for four days before and more than 24 hours after symptoms first appeared.
The researchers wanted to establish the factors that might heighten or lessen the risk of subsequently catching the virus within the incubation period of 14 days from the start of the infected person’s symptoms.
Writing in BMJ Global Health, the researchers say that secondary transmission occurred in 41 out of the 124 families, with 77 adults and children being infected in this way, giving an “attack rate” of 23%.
Thirteen out of the 36 children (36%) in the study became infected, compared with 64 out of 92 (69.5%) adults.
Twelve of the children had mild symptoms and one had none, while 83% of the adults had mild symptoms, one in 10 had severe symptoms, and one person became critically ill.
Daily use of disinfectants, window opening, and keeping at least one metre apart were associated with a lower risk of passing on the virus, even in more crowded households, but the researchers found that daily contact and the number of family members wearing a face mask after the first person developed symptoms were associated with a heightened risk.
Four factors were significantly associated with secondary transmission of the virus: diarrhoea in the first person to become infected and close daily contact with them quadrupled the risk of passing on the virus, while close daily contact, such as eating meals round a table or watching TV together, was associated with an 18-fold increased risk.
Frequent use of bleach or disinfectants for household cleaning and the wearing of a face mask at home before symptoms emerged, including by the first person to have them, were associated with a reduced risk of viral transmission.
A face mask worn before symptoms started was 79% effective, and disinfection 77% effective, at stopping the virus from being passed on.
Although the authors acknowledge limitations to their study, they say: “This study confirms the highest risk of household transmission being prior to symptom onset, but that precautionary [non-pharmaceutical interventions], such as mask use, disinfection and social distancing in households can prevent Covid-19 transmission during the pandemic,” independent of household size or crowding.
“Household transmission is a major driver of epidemic growth,” they point out, adding that their findings could be used to “inform precautionary guidelines for families to reduce intrafamilial transmission in areas where there is high community transmission or other risk factors for Covid-19”.
Meanwhile, a study in England by University College London has found that strict adherence to the UK government’s Covid-19 lockdown guidelines and overall confidence in government are at all-time lows.
Its social study of more than 90,000 adults during the coronavirus epidemic, which was launched in the week before lockdown, shows that complete compliance of following government recommendations has decreased in the past two weeks from an average of 70% of people to just over 50%.
Compliance levels amongst younger adults were even lower, with only 40% reporting ‘completely’ complying with lockdown rules.
When asked how much confidence they had in the Government’s handling of the Covid-19 epidemic on scale of one (not at all) to seven (lots), the study found a further decrease in confidence over the bank holiday weekend – from about 4 to about 3.5.
Confidence fell most sharply among respondents under 30, those in urban areas and those with a mental health diagnosis. Confidence in government is lower in England than in Scotland and Wales, where lockdown easing has not yet taken place.
Lead author Dr Daisy Fancourt, of UCL Epidemiology & Health Care, said: “Compliance with government advice continues to fall, but still remains relatively high amongst most groups. Confidence in government also continues to fall in England since the easing of lockdown was announced, dropping most noticeably over the bank holiday weekend.”
Wang Y, Tian H, Zhang L et al. Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China. BMJ Global health 29 May 2020.
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