Virus World

Updated guidance from the US Centers for Disease Control and Prevention says people fully vaccinated against Covid-19 do not need to wear masks or practice social distancing indoors or outdoors, except in certain circumstances.

People fully vaccinated against Covid-19 do not need to wear masks or practice social distancing indoors or outdoors, except under certain circumstances, the director of the US Centers for Disease Control and Prevention announced Thursday. "If you are fully vaccinated, you can start doing the things that you had stopped doing because of the pandemic," Dr. Rochelle Walensky said during a White House Covid-19 briefing. "We have all longed for this moment when we can get back to some sense of normalcy."  Calling it an "exciting and powerful moment," Walensky said the science supports the updated CDC guidance that "anyone who is fully vaccinated can participate in indoor and outdoor activities -- large or small -- without wearing a mask or physical distancing." She cited three studies -- one from Israel and two from the United States -- that show vaccines work.  The Israeli study, which was published in the Journal of the American Medical Association, showed the vaccine was 97% effective against symptomatic Covid-19 and 86% effective against asymptomatic infection in over 5,000 health care workers. There have been reports of "breakthrough" infections among vaccinated people in the United States -- a small number among more than 117 million people in the United States who are now fully vaccinated. Walensky noted that "the resulting infection is more likely to have a lower viral load, may be shorter in duration, and likely less risk of transmission to others."

One-third of passengers aboard a bus were infected by a fellow passenger, scientists reported. In late January, as the new coronavirus was beginning to spread from China’s Hubei Province, a group of lay Buddhists traveled by bus to a temple ceremony in the city of Ningbo — hundreds of miles from Wuhan, center of the epidemic. It was a sunny day with a gentle breeze, and the morning service was held al fresco, followed by a brief luncheon indoors. A passenger on one of the buses had recently dined with friends from Hubei. She apparently did not know she carried the coronavirus. Within days, 24 fellow passengers on her bus were also found to be infected. It did not matter how far a passenger sat from the infected individual on the bus, according to a study published in JAMA Internal Medicine on Tuesday. Even passengers in the very last row of the bus, seven rows behind the infected woman, caught the virus. The only factor that may have mitigated the risk of infection was sitting near a window that could be opened, or near the door.

The incident adds to a large body of evidence indicating that the coronavirus can be transmitted by tiny particles that linger in the air, and not just through large respiratory droplets that fall quickly to the ground. The World Health Organization acknowledged the virus may be airborne in July and that these particles may seed superspreader events in closed spaces like restaurants and workplaces. The new study “adds strong epidemiological evidence that the virus is transmitted through the air, because if it were not, we would only see cases close to the index patient — but we see it spread throughout the bus,” said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech and a leading expert on airborne viruses.  The two buses carrying passengers to the event had cooling units that were recirculating air inside the vehicles. “That would facilitate the virus in the air and spread it around the bus,” Dr. Marr said. None of the 60 passengers on the second bus was infected.

Dr. Muge Cevik, an expert on infectious diseases and virology at the University of St. Andrews School of Medicine in Scotland, said that the outbreak was likely caused by a combination of factors: a long trip, a confined environment, a crowded bus and an individual who was probably extremely contagious because she was in the early stages of the infection. “There isn’t really a dichotomy between aerosol and droplet transmission,” Dr. Cevik said. “There have to be multiple things happening at the same time for this type of high risk transmission to occur. This was the wrong place, the wrong time, the wrong person.” The study’s authors, who are physicians with the Chinese Center for Disease Control and Prevention, concluded that “future efforts at prevention and control should consider the potential for airborne spread of Covid-19.” The study was published previously online as a preprint. The outing to the Buddhist temple was what scientists refer to as a natural experiment. It took place on Jan. 19, when there were still no confirmed Covid-19 cases reported in Ningbo. The circumstances conveniently allowed for a comparison between similar passengers on two different buses. Some 300 people attended the temple ceremony, but only 128 made the 50-minute trip by bus. One bus carried 68 passengers, including the individual who was infected, while the second bus carried 60 people. None of the worshipers wore masks. The paper in JAMA Internal Medicine does not describe the infected individual and says the person did not have symptoms until the after returning from the temple. But a version of the study published in China says the individual was a 64-year-old woman and that she developed symptoms on Jan. 18, a day after dining with guests from Hubei and a day before going to the temple. She took medicine but did not see a doctor...

Study published in JAMA (Sept. 1, 2020):

https://doi.org/10.1001/jamainternmed.2020.5225 

From good ventilation to redesigning spaces, here are ways to help reduce the risk of transmission in closed settings. With the winter season upon us in the Northern Hemisphere, cold weather conditions are forcing people to stay indoors. Coupled with children heading back to school and offices reopening, there is looming concern around a second wave of the coronavirus in Europe, North America and other parts of the world. COVID-19 is a highly contagious respiratory disease. In closed and crowded indoor settings, there is a higher risk of it spreading compared with the outdoors, where the flow of fresh air can dilute and dissipate the virus particles. According to the WHO, the coronavirus is primarily transmitted by droplets spread through direct or close contact with an infected person, and indirect contact with contaminated surfaces, also known as fomite transmission. But there is also the possibility of airborne transmission in crowded indoor settings with poor ventilation, such as restaurants, gyms, night clubs and offices. A number of measures can be taken to reduce the risk of infection in such closed settings.

Natural ventilation

Ventilation is the introduction of fresh air into an indoor space while the stale air is pushed outside.  Whether at home or in public buildings, such as schools and offices, ventilation can be improved by simply opening windows and doors whenever possible. Luca Fontana, a water, sanitation and hygiene (WASH) specialist consultant at the WHO, told Al Jazeera ventilation is “one part of the big package of infection prevention and control measures” along with physical distancing, hand hygiene and face masks. “The general proposal of ventilation in the building is to provide healthy air for breathing by both diluting the pollutant originating in the building and removing the pollutant from the space itself,” he said in a recent Facebook live Q&A.

HVAC systems

In public spaces, ventilation through mechanical measures like heating, ventilation and air conditioning (HVAC) systems can be helpful in improving indoor air quality. According to the WHO, a well-maintained and operated HVAC system can reduce the spread of COVID-19 in indoor spaces by increasing the rate of air change, reducing recirculation of air and increasing the use of outdoor air. The air should preferably not be recirculated and the HVAC systems should be regularly inspected, maintained and cleaned by professionals. The WHO has outlined technical specifications for operating and maintaining these systems in the context of COVID-19.  

Filters and fans

High-efficiency particulate air (HEPA) filters that are commonly used in aeroplanes and hospitals are another useful tool to remove viruses and germs from the atmosphere. These can minimise the duration of the exposure to any potential infectious materials produced by a cough or sneeze. The use of fans, with certain considerations, can improve air circulation and reduce pockets of stagnant air in an enclosed space. “A table or pedestal fan is safe for air circulation among family members living together who are not infected with the virus that causes COVID-19,” said Maria Neira, director of the department of public health and environment at the WHO. “However, fans should be avoided when people who are not part of the immediate family [are present], since some people could have the virus despite not having symptoms,” she added. “Air blowing from an infected person directly at another in a closed space might increase the transmission of the virus from one person to another.” When using a ceiling fan, Fontana said it was important to maintain good ventilation – by opening a window for instance – as an efficient way to increase the exchange of air between indoors and outdoors...

It is essential to understand where and how SARS-CoV-2 is transmitted. Case reports were extracted from the local Municipal Health Commissions of 320 prefectural cities (municipalities) in China, not including Hubei province, between 4 January and 11 February 2020. We identified all outbreaks involving three or more cases and reviewed the major characteristics of the enclosed spaces in which the outbreaks were reported and associated indoor environmental issues. Results: Three hundred and eighteen outbreaks with three or more cases were identified, involving 1245 confirmed cases in 120 prefectural cities. We divided the venues in which the outbreaks occurred into six categories: homes, transport, food, entertainment, shopping, and miscellaneous. Among the identified outbreaks, 53.8% involved three cases, 26.4% involved four cases, and only 1.6% involved ten or more cases. Home outbreaks were the dominant category (254 of 318 outbreaks; 79.9%), followed by transport (108; 34.0%; note that many outbreaks involved more than one venue category). Most home outbreaks involved three to five cases. We identified only a single outbreak in an outdoor environment, which involved two cases....

The first salient feature of the 318 identified outbreaks that involved three or more cases is that they all occurred in indoor environments. Although this finding was expected, its significance has not been well recognised by the community and by policy makers. Indoors is where our lives and work are in modern civilisation. The transmission of respiratory infections such as SARS-CoV-2 from the infected to the susceptible is an indoor phenomenon. Our study does not rule out outdoor transmission of the virus. However, among our 7,324 identified cases in China with sufficient descriptions, only one outdoor outbreak involving two cases occurred in a village in Shangqiu, Henan. A 27-year-old man had a conversation outdoors with an individual who had returned from Wuhan on 25 January and had the onset of symptoms on 1 February. 

This study shows that the individual indoor environments in which we live and work are the most common venues in which the virus of the once-in-a-century-pandemic is transmitted among us. An individual infected in one building may infect others in the building(s) that he or she later visits. People are in constant contact as they move from one indoor space or building to another, which creates an indoor contact network through which a virus can spread.17 The buildings and transport cabins in various parts of the world are thus connected and facilitated the spread of the COVID-19 pandemic virus. In conclusion, all identified outbreaks of three or more cases occurred in an indoor environment, which confirms that sharing indoor space is a major SARS-CoV-2 infection risk.

Preprint available in medRxiv (April 7, 2020): https://doi.org/10.1101/2020.04.04.20053058