In this fast-moving pandemic, demand for accurate information is insatiable. How does WHO arrive at the best guidance for the world? What is its latest advice on hot-button questions regarding airborne transmission, wearing masks, and carriers with no symptoms?

As COVID-19 evolves, the World Health Organization (WHO) continues to lead the herculean global fight against the virus, providing countries with real-time technical expertise and essential equipment, regularly updating the public, and coordinating international bodies and national governments in responding to the pandemic.

With such a fast-moving situation, there is a pressing demand for reliable information. The agency has faced criticism about how much time it takes to release its guidance and what may be perceived as changing advice. But the bottom line is that WHO relies on science-based evidence to update its COVID-19 advice for the public and technical guidance for the entire world, and, while moving as quickly as possible to keep the public informed, this takes time. Since January, WHO has published more than 140 guidance documents about COVID-19, along with 103 online training courses in 34 languages.

Recent WHO guidance updates include the following:

Aerosol Transmission

Many people have wondered if COVID-19 can be transmitted through the air, a process known as aerosol transmission. On Jan. 10, WHO recommended taking specific precautions against airborne or aerosol transmission only in hospital settings during procedures such as inserting a breathing tube into a patient.

Since then, new evidence has shown that outbreaks of COVID-19 have occurred in some restaurants and other public places where people may be shouting, talking, or singing. Given those outbreaks, WHO decided recently that aerosol transmission cannot be ruled out in crowded, inadequately ventilated indoor locations where people spend long periods of time with others. After assessing the new evidence, WHO issued revised and additional guidance that now advises wearing masks when physical distancing is difficult and avoiding crowded, enclosed spaces with poor ventilation to help deter this potential form of transmission. WHO also acknowledged that more evidence is needed to help further shape guidance on aerosal transmission and said it welcomes the scientific and medical communities’ input in shaping this information.

Wearing Masks

As more and more evidence has shown that face coverings help limit the spread of COVID-19 in areas where physical distancing isn’t feasible, WHO has updated its guidance for the public to help point to nonmedical/fabric masks as a key method of protection. Below is the latest guidance from WHO on both medical and nonmedical masks.

Medical masks: WHO recommends these masks for health workers, people with any symptoms, and those caring for someone with COVID-19. They are also recommended for at-risk people, such as those with underlying health conditions or those over 60 years old.

Nonmedical, fabric masks: advises governments to encourage the general public to use nonmedical fabric masks in areas with widespread transmission, especially on public transport or in shops and anywhere else where physical distancing is not possible.

Asymptomatic Carriers

Infected people without symptoms can still spread the virus and should isolate to break chains of transmission. Not only is the possibility of asymptomatic transmission another reason for people to wear masks and keep physically distant, but it also underlines the critical importance of widespread testing with a short turnaround time to obtain results. The mayor of Atlanta, Keisha Lance Bottoms, said that she and her family got tested as a precaution after attending a funeral. They had to wait several days for the results, during which her husband became ill. The test results finally showed their son was infected but asymptomatic, and he may have infected his father while they waited for the results. Asymptomatic transmission with slow testing also makes contact tracing — another critical weapon in fighting COVID-19 — harder. WHO says, “it is important that all people who are infected are identified by testing, isolated, and receive medical care.”

How the Guidance Gets Made

 People are understandably impatient to hear definitive health guidance, but the very nature of the scientific method requires WHO to base its judgments on the best current data and to change its guidance as new information becomes available. It is important to remember the progress that has already been made in such a short time and in the face of the most serious health challenge our global society has faced in 100 years: This was a completely unknown disease a little over six months ago.

Scientists are working around the clock to understand more about COVID-19 and how to contain it. WHO, the only truly global health organization with 194 member states, is leading the COVID-19 response and coordination for the entire world. Because of this, it must rely on substantial evidence to create guidance for different demographics and populations. At a recent WHO press briefing, WHO’s chief scientist, Dr. Soumya Swaminathan, explained the comprehensive process WHO uses to update guidelines.

The way WHO makes guidance is “not impulsive,” she said. “It’s not done on a day-to-day basis but it’s a process that continues and will continue, I’m sure, with COVID for the weeks and months to come.”

Scientists are learning new things about COVID-19 very rapidly, and the global demand for information is relentless. News reports pick up on any development, including research that is preliminary, or findings that hold true for a small segment of the population at one specific point in time, but not necessarily in new settings or in larger numbers. The habit of publishing preprint research — before peer review has been completed — has led to some premature headlines. That’s why WHO conducts a systematic review of around 500 publications a day, and sometimes, up to 1,000, to understand and synthesize the science being conducted all over the world and to ensure it can be proven to keep people safe. This data is then peer-reviewed to be certain that it is of the highest quality. Every week, WHO updates its review based on the assessments made by scientists who are part of a guideline development group.

After reviewing the scientists’ evidence, WHO issues a public health recommendation.

“Communicating complex science in real time about a new virus is not always easy,” said WHO Director-General Dr. Tedros Adhanom Ghebreyesus. “We can always do better. We welcome constructive debate, and that’s how science advances.”

An example of WHO’s scientific collaboration is its Research and Development Blueprint, which strengthens coordination between scientists and global health professionals to respond to the pandemic. In early February, more than 300 scientists from around the world met to identify gaps in COVID-19 research and align on research priorities. The group reconvened in July to discuss updates and new findings. These sessions seek to bring the best minds together and stimulate global research coordination.

Another group aiding the scientific community during the COVID-19 pandemic is the WHO’s Strategic and Technical Advisory Group for Infectious Hazards, which provides independent analysis to WHO’s emergencies program. It reviews information about disease outbreaks and gives technical advice to WHO about how to prioritize strategies. The group has been assisting with assessing the global context of infectious diseases since it was created in response to the Ebola outbreak.

Throughout the course of the COVID-19 pandemic, and previous global health emergencies, such as H1N1 (swine flu) and Ebola, WHO continuously works to transparently share what it knows and what it is uncertain about while promoting new research and constructive discussion. For example, it recently updated its risk assessment tools for mass gatherings, religious gatherings, and sports events to guide event organizers during the pandemic.

As new information about COVID-19 is released, WHO will continue to work with experts to review data and publish guidance at the appropriate time.

“We take this very seriously,” Swaminathan said. “Any guidance that we put out has implications, of course, for billions of people around the world, so it has to be carefully considered before it is done.”

Maya Punjwani also contributed to this article.