LAUSR

A man is walking on a side road and wearing a face mask. A man is standing inside his room looking outside through a window. A man is sitting at his desk at home, a requirement of his quarantine due to a positive test for COVID-19. A man is lying on a bed, with an oxygen mask covering his face inside a care facility. With SARS-CoV-2 still not preventable, these scenes are still happening. Countless efforts with nonpharmaceutical interventions (NPI), including wearing face masks, frequent handwashing, distancing oneself socially and avoiding the three C’s (e.g., closed places, crowded places, close contact settings) and even getting vaccinated, are still not sufficiently slowing down transmission. As of 28 May 2021, more than 1.5 billion people worldwide have received their COVID-19 vaccination. Nearly 550,000 new cases were seen that day (https:// covid19.who.int/). The purpose of this letter is to recommend to World Health Organization (WHO) that they carefully review and revise their current recommendations to underscore the fact that SARS-CoV-2 continues to have a high transmission rate because virus-containing exhaled droplets that travel over considerable distances play a fundamental role in the spread of this infection [1,2]. The WHO has recommended that the major route of transmission of SARS-CoV-2 is through air droplets (> 5 μm) as well as aerosol-generating procedures (< 5 μm) in health care settings. On this basis, WHO has issued recommendations (in March, July, and December 2020) to continue to practice NPI, get vaccinated as soon as possible, and use personal protective equipment (PPE) when caring for patients suspected of COVID-19 infection. In March 2021, WHO recommended installing heating, ventilation, and air conditioning (HVAC) systems for healthcare, non-residential and residential settings to ensure good indoor air flow. Yet, what this document lacks are data to explain whether SARS-CoV-2 poses a serious airborne transmission risk. In May, the US Centers for Disease Control and Prevention (CDC) have updated their recommendations on the prevention of COVID-19 transmission. The updated document clearly acknowledges that airborne transmission is the route of SARSCoV-2 infection [3] based on evidence suggesting that people release respiratory fluids during quiet or forced exhalation (e.g., breathing, speaking, singing, exercise, coughing or sneezing) in various sizes of droplets. These droplets can stay in the air from seconds to hours and travel well beyond 6 feet [4]. Debate may exist among scientists [5], but most agree [4,6–9] on the airborne transmission of SARSCoV-2. In the early days of the pandemic, conducted experiments that suggested that aerosol and fomite transmission of SARS-CoV-2 was plausible. Their experiments showed that the virus can remain viable and infectious in aerosols for hours and as long as several days on surfaces. Last June, a group of 239 scientists appealed to WHO to clearly state that the COVID-19 virus is most commonly spread from personto-person through the air via tiny respiratory droplets expelled from sneezing, coughing, talking, laughing or breathing [7]. The letter urged that the denial of airborne transmission of SARS-CoV-2 and the lack of clear recommendations as to control measures against SARS-CoV-2 may have significant consequences for human health, as well as engendering massive social and economic losses. Meanwhile, in October, a joint group from the University of Mississippi and Johns Hopkins University created a mathematical model to better understand how SARS-CoV-2 spreads. This model is known as Contagion Airborne Transmission or CAT [8]. Ten months have passed since these petitions were made. While the airborne transmission of SARS-CoV-2 risks continues to be underestimated [10,11], many people falsely believe they are fully protected against COVID-19 (by NPI, vaccinations, and PPE). If these theories are true, transmission of SARS-CoV-2 continues via airborne transmission and is spread not only by close contacts but also by more distant ones. Because small droplets diffuse in indoor environments for distances up to 10 meters in circumference, people