Masks can reduce Covid-19 growth rate by 40%: Study

M asks can reduce the growth rate of coronavirus infection by 40%, a paper on the impact of the staggered use of masks in public places in different cities and municipalities in Germany has found.

After the city of Jena made it mandatory on April 6 to wear masks, new confirmed Covid-19 infections reduced by 25% compared to that in a group with similar demographics, local health care systems and pre-April Covid-19 levels, the analysis found. The findings were released on Friday. “Depending on the region we analyse, we found that face masks reduced the cumulative number of registered Covid-19 cases between 2.3% and 13% over a period of 10 days after they became compulsory. Assessing the credibility of the various estimates, we conclude that face masks reduce the daily growth rate of reported infections by around 40%,” said the discussion paper by IZA Institute of Labor Economics in Bonn, Germany.

The long incubation period of the Covid-19 infection, among other factors, contribute to its spread, according to experts. Symptoms appear on average after four to five days of getting infected, according to a study published in March in The Annals of Internal Medicine. In this period, patients might not develop symptoms of cough, fever or difficulty in breathing, but can spread the infection.

Several studies have also found that Covid-19 is also spread by those who have a very mild disease but do not show symptoms.A paper published in New England Journal of Medicine on Friday, which followed asymptomatic and pre-symptomatic cases on the Diamond Princess cruise ship that saw an outbreak in February, found that the majority of asymptomatic cases did not develop symptoms at all throughout the course of the infection.

People with advancing age, hypertension and diabetes were pre-symptomatic for longer, it found. “This important study clarifies many facts. People develop symptoms in an average of four days, and a large proportion of Covid-19 positive patients (58%) are asymptomatic throughout the duration of illness, which ranges from three to 21 days, with the median period being nine days. The study also found that asymptomatic patients transmit infection throughout the duration of illness,” said Prof GC Khilnani, chairman, pulmonary, critical care and sleep medicine, PSRI, and the former head of the pulmonology department at Delhi’s All India Institute of Medical Sciences.

At least 28% of 40,184 people who tested positive for Covid-19 between January 22 and April 30 in India were asymptomatic, according to an Indian Council of Medical Research (ICMR) study.

Wearing masks in public is already compulsory or recommended for all in several countries, including India, Singapore, France, Spain, Germany and Argentina, among others. A study in The Lancet on June 2 said social distancing, masks and hand hygiene do not offer complete protection on their own.

“As the lockdown lifts and people become mobile, social distancing, wearing masks and hand washing are the only defence against Covid-19 till we get an effective vaccine or cure,” said Dr Ambarish Dutta, associate professor of epidemiology and public health, Indian Institute of Public Health, Bhubaneswar.

The World Health Organization (WHO) updated its guidelines for countries earlier this month and advised “governments to encourage the general public to wear masks where there is widespread transmission and physical distancing is difficult, such as on public transport, in shops or in other confined or crowded environments”.

Two days later, the global health agency was forced to retract a statement by its coronavirus lead, Maria Van Kerkhove, who said asymptomatic transmissions were “very rare”. It triggered a global debate and led sceptics to use the remark to discredit mandatory masks and social distancing policies. WHO clarified that much remains unknown about asymptomatic transmission. “Most transmissions seem to occur from those with symptoms. However, we have to be careful because people can be infectious one to two days before they develop symptoms. So right now it is important for everyone to wear face coverings when they cannot maintain physical distancing,” said Dr Soumya Swaminathan, chief scientist, WHO, Geneva.