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Face masks reduce the risk of spreading large Covid-linked droplets when speaking or coughing by up to 99.9 per cent, according to a lab experiment with mechanical mannequins and human subjects, researchers said on Wednesday.

A woman standing two metres from a coughing man without a mask will be exposed to 10,000 times more such droplets than if he were wearing one, even if he is only 50 centimetres away, they reported in the journal Royal Society Open Science.

“There is no more doubt whatsoever that face masks can dramatically reduce the dispersion of potentially virus-laden droplets,” senior author Ignazio Maria Viola, an expert in applied fluid dynamics at the University of Edinburgh’s School of Engineering, told.

Large respiratory droplets – which act like projectiles before being pulled toward the ground by gravity – are thought to be the main driver of SARS-CoV-2 transmission, he noted.

“We continuously exhale a whole range of droplets, from micro-scale to millimetre-scale,” Maria Viola said by phone.

“Some of the droplets will drop faster than others” depending on temperature, humidity and especially air speed, he said.

The study focused on particles larger than 170 microns in diameter – roughly two to four times the width of a human hair.

Aerosol particles, which tend to follow currents in the air, are generally described as smaller than 20 or 30 microns.

Intermediate size droplets can behave either way, the study found.

“If you wear a mask, you are mitigating the virus transmission by an order of magnitude – 10 times less,” Maria Viola said.

“In our study, for the larger droplets we measure, we’re talking about 99.9 per cent less.”

According to the Institute for Health Metrics and Evaluation (IHME) in Seattle, Washington, 55,000 lives could be saved in the United States over the next four months if a policy of universal mask use were adopted.

The Institute’s modellers – who accurately predicted in mid-July that Covid-19 deaths in the US would top 224,000 by Nov 1 – project 561,000 deaths on current trends by April 1, 2021.

Universal mask-wearing would reduce the global death toll by 400,000 over the same period, from 2.9 million to 2.5 million, they calculate. To date, the virus has claimed about 1.7 million lives.

Earlier this month, the World Health Organisation (WHO) updated its Covid-19 guidance on masks to recommend they be worn indoors in the presence of other people if ventilation is inadequate.

The guidelines apply especially in areas of known or suspected community transmission.

Masks serve primarily to reduce the emissions of virus-laden droplets by people when they cough, sneeze, sing, talk or simply breathe, but they can also help prevent the inhalation of droplets by the person wearing them.

California became the first state on Wednesday to pass the grim mark of 2 million cases of the coronavirus, just six weeks after hitting the 1 million mark, according to data from Johns Hopkins University. California’s infection rate — in terms of the number of cases per 100,000 people — is lower than the U.S. average but, with 40 million residents, it outpaces other states in sheer numbers.

More than 23,600 Californians have died from the virus since the pandemic began.

The state has seen its number of cases climb exponentially in recent weeks, followed by soaring rates of hospitalizations and deaths that have overwhelmed intensive care units and prompted hospitals to put emergency room patients in tents and treat others in offices and auditoriums.

Pleas to avoid social gatherings for the holidays rang with special desperation in Southern California. Los Angeles County is leading the surge, accounting for one-third of the COVID-19 cases in the state and nearly 40% of its deaths.

Thanksgiving gatherings in California in which people ignored mask-wearing and social-distancing rules have been blamed for spreading the infection and another surge from the Christmas holidays could push stressed medical systems over the brink, officials are warning.

Medical workers are discouraged and outraged over scenes of crowded outdoor malls, packed parking lots, and parents and children walking around without masks, county Health Services Director Dr. Christina Ghaly said.

If LA County continues to see the same growth in COVID-19 infections in the next two weeks, hospitals may find themselves having to ration care because of a lack of medical staff, Garcetti said. “That means the doctors will be forced to determine who lives and who dies,” he said.

The transmission rate — the number of people that one infected person will in turn infect — has been slowing for nearly two weeks. The rate of positive cases reached a new high of 12.3% over a two-week period but was starting to trend down over the last seven days, from a peak of 13.3% to 12.6%.

The number of new positive cases dropped to a relatively modest 39,069, given that California has been averaging nearly 44,000 newly confirmed cases a day.

The state also had nearly 1,000 health workers assisting at 91 facilities in 25 of the state’s 58 counties, and is opening a fifth alternative care site in San Diego County.

The California National Guard was setting up about 200 beds on vacant floors of the Palomar Health Center near San Diego, within the existing hospital complex, said Brian Ferguson, a spokesman for the Governor’s Office of Emergency Services. It could begin accepting patients Christmas Day, relieving overburdened hospitals particularly in nearby Imperial County.

California expects more federal medical workers to arrive by the weekend, and Gov. Gavin Newsom said he expects more of the 3,000 contract health care workers the state is seeking to arrive after the holidays.

A Japanese health ministry panel said on Friday that people aged 65 or older should get priority for vaccination against COVID-19 as the government sets guidelines that will also prioritise frontline healthcare workers and those with medical conditions.

The panel also specified chronic heart disease, chronic respiratory disease and chronic kidney disease, among others, as underlying conditions that should determine priority for the vaccine.

The recommendations would include 36 million elderly people and 8.2 million people with medical conditions in the first group to receive vaccine shots.

Another government panel this week recommended that priority be given to frontline medical professionals and workers at elderly care facilities, while the elderly and those with underlying health conditions should also receive priority.

Japan is currently facing a third wave of coronavirus infections, putting the nation’s medical system under heavy strain.

Half of the air samples that were taken from several hospital hallways, ICUs and a fifth from bathrooms had high levels of coronavirus, a study has suggested. In fact, the air sampled in the ICUs were found to be more contaminated than the non-ICUs.

The researchers have found that 17 per cent of air sampled from close patient environments was positive for SARS-CoV-2 RNA and one-quarter of all ICU rooms with Covid-19 patients were contaminated from the virus.

The study said 82 of 471 air samples (17.4%) from close patient environments were positive for SARS-CoV-2 RNA, with a significantly higher positivity rate in intensive care unit settings (intensive care unit, 27 of 107 [25.2%] vs non-intensive care unit, 39 of 364 [10.7%].

“Among 2284 records identified, the positivity rate was 5 of 21 air samples (23.8%) in toilets, 20 of 242 (8.3%) in clinical areas, 15 of 122 (12.3%) in staff areas, and 14 of 42 (33.3%) in public areas came back as positive,” the study said.

For the study, the researchers looked for articles covering coronavirus and air contamination between January 1 and October 27. Of the 24 studies, 10 were from China, the United States, Hong Kong, Korea, Singapore, Iran, the United Kingdom and Italy.

The air samples were taken from close patient environments, in clinical areas away from patients, in staff areas, in toilets and/or bathrooms, and 6 in public areas.

“The results of the positivity rate in ICU and non-ICU patient environments were highly heterogeneous and appeared superior in the ICU when pooling the results. In the ICU, 7 of 12 studies did not find SARS-CoV-2 RNA, whereas the remaining did, with 37.5% to 100% positive samples,” it said.

However, the study said the level of severity of patients’ infections was not associated with increased air contamination.

据沈阳卫健委网站消息，现将1例沈阳市韩国返沈人员新冠肺炎确诊病例尹某某的密切接触者新冠病毒核酸检测阳性的情况通报如下：

一、患者基本情况

郑某某，女，16岁，中国籍，家庭住址：沈阳市于洪区北陵街道向工街宏达家园，学生，是沈阳市韩国返沈人员确诊病例尹某某的外孙女。郑某某作为尹某某的密切接触者，于12月22日进行核酸检测，结果为阴性，12月24日，沈阳市疾控中心再次进行核酸检测，结果为阳性。沈阳市卫生健康委立即启动转运程序，将患者转入市第六人民医院进行进一步的诊断治疗。目前，经专家组会诊诊断为新冠肺炎确诊病例（普通型）。

二、目前采取的措施

一是积极救治患者。由市六院医疗救治专家团队，制定救治方案，全力救治患者。

二是深入排查密切接触者。截止目前共排查密切接触者278人，立即转入隔离点实施集中隔离医学观察，并进行核酸检测，检测结果均为阴性。

三是科学划定疫点。根据患者活动范围，初步划定疫点2个，由市区两级疾控中心对上述疫点进行终末消毒，并进行消毒效果评价，切断传播途径，彻底消除传播风险。