By Jane Nguyen, Shahira Ellaboudy

It’s nine months into the COVID-19 pandemic, and if you don’t feel confused –  well, you haven’t been paying attention. For the better part of a year now, our world has been trying its best to understand the predator that has now taken almost two million lives: a microscopic collection of proteins, nucleic acids, and greasy fat molecules known as SARS-CoV-2.

Viruses are incredibly quick to evolve. This novel coronavirus outpaced its SARS and MERS predecessors (Abdelrahman et al., 2020) as it spread across continents at unprecedented rates. So, when scientists began scrambling in March to characterize the rapid infection patterns of SARS-CoV-2, they were at a loss on how to contain the spread. It is no surprise that some of the safety guidelines championed at the beginning of the pandemic do not match what scientists know now. And although the pandemic is undoubtedly taking its toll on all of us, taking the most effective precautions saves lives. We need only look to recent headlines to find upward of 2 million reasons (Dong et al., 2020) for us to keep up the fight.

So, why does the information keep changing? Original recommendations of hand-washing and six feet’s social distance derive from research previously conducted on viruses similar to SARS-CoV-2, but not exactly the same (Wells 1934, Olsen et al. 2003). Here, we intend to provide an update on what science has learned about curbing transmission in the last nine months that will hopefully clear up some confusion.

When protecting oneself from COVID-19, people are encouraged to practice three basic rules: 1) wear a mask, 2) wash your hands, 3) keep a social distance of at least 6 feet. These set of standards have been proven to lower SARS-CoV-2 transmission and infection rates in places that abide by all of them (Doung-ngern et al., 2020).

Earlier in the year, the CDC encouraged people to sanitize hard surfaces such as wooden tables and metal door handles. SARS-CoV-2 was believed to primarily transmit through large droplets and fomites, similar to other respiratory viruses (Boone et al., 2007). Preliminary data supporting indirect transmission through surfaces and lack of viral RNA in air samples (Ong et al., 2020) emphasized hand hygiene and surface sanitization. As people and scientists alike yearned for the closest solution, their eyes turned to viral YouTube hits about proper hand washing techniques and even tutorials on how to sanitize groceries. Air transmission was controversial and had not been observed early on (Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19), 2020). This overshadowed the priority of wearing masks, until recently.

Unlike other countries, the United States did not officially advise wearing masks for five weeks into the pandemic. It wasn’t until April that the CDC reversed its position on masks. By summer, overwhelming evidence shifted the tide towards the prevalence of airborne transmission as 200+ scientists released a statement urging the world to recognize the potency and prevalence of airborne transmission. The virus appears to spread efficiently via aerosols in submicroscopic droplets (<5 μm) (van Doremalen et al., 2020). These aerosols can be highly infectious from a simple act of speaking (Stadnytskyi et al., 2020) and can extend far beyond 6 feet. New data show that while the half-life of infectious aerosols is 1.1 hours, viral deactivation in the air is very gradual, and infectious viruses can still linger for as long as 16 hours (van Dormalen, et al., 2020, Fears et al., 2020). By October, the CDC finally acknowledged the high risk of airborne transmission, but mainly attributed transmission to close contact. New evidence suggests otherwise.

A recent report from the Journal of Korean Medical Science shed light on a COVID-19 infection that occurred between customers at least 21 feet apart at an indoor restaurant (Dong et al., 2020; Kwon et al., 2020). The diners were exposed for only 5 minutes without any direct or indirect contact. A different study in July alarmed the scientific community documenting the spread of COVID-19 of just one infected customer to ten other diners, most of whom much farther apart than six feet (Lu, et al., 2020). Moreover, a retrospective study conducted by the CDC found that individuals who dine at restaurants were twice as likely as those who didn’t to have received a positive SARS-CoV-2 test result (Fisher, et al., 2020).

These data conflict with current regulations. If the virus is in the air that we breathe, what is safe anymore? Previous reopening guidelines are now under question: Are restaurants unsafe? Is 6 feet apart not enough? Can this happen in other indoor places like gyms and supermarkets?

When dissecting the scene further, researchers found that the long-distance infections traced back to the restaurant were likely due to improperly worn masks and aerosol droplets carried by air flow confined indoors. This corroborates the accounts of recent studies that identify airborne transmission as the source of many coronavirus transmission events (Shen, et al., 2020, Nielsen, et al., 2020). Many now suggest that this new knowledge desperately warrants some re-writing of the “rules.”

How do these additional factors influence the effectiveness of precautions we are currently taking? Even seemingly cautious people may wonder whether these precautions should be practiced at all. To understand the impact of each precaution and how it holistically contributes to the overall probability of transmission, let’s look at some newer statistics and discuss relative probabilities of infection.

SARS-CoV-2 can be viewed as one very deadly probability game — a classic marbles-in-bag situation. There’s nothing that can completely keep you from drawing the “COVID-19 marble,” but there are certainly things you can do to change the relative frequency of COVID-19 marbles in your particular pandemic bag, so to speak. And the difference matters.

The one thing everyone can do to reduce airborne transmission is to wear a face mask and wear it correctly – entirely covering the mouth, nose, and chin area. This also includes efforts to minimize touching your mask. Yet, not all masks are created equal.

Efficacy of common mask types measured by relative droplet emission. Data in table obtained from (Fischer et al., 2020). Rubbing your mask, especially single-layer cloth ones, fragments and dislodges large droplets into aerosolized particles (Asadi et al., 2020). The mechanical simulation from your hands, lips, and nose increases droplet counts and particle emission rates from neck gaiters and bandanas compared to not wearing a mask. Meanwhile, valved N95 masks increase airflow from the mask wearer, putting surrounding people at risk. Although masks do prevent airborne transmission, be aware that some prove to be counterproductive.

Face masks are vital to prevent transmission, but are not enough to overcome this virus alone. It takes a combination of other precautions to significantly lower infection risks. Yet, we are all human and it is not always possible to practice all effective precautions at once. For example, eating requires you to take off your mask, you have to go into a grocery store where social distancing isn’t strictly enforced, where social distancing is not possible, or you forgot to wash your hands and accidentally touched your eyes.

Given that it is impossible to keep all aspects of COVID-19 safety on your mind at all times, it’s important to prioritize some precautions over others The key is to realize that no single precaution can provide absolute immunity from the virus, but if practiced in unison and correctly, they will significantly decrease the risk of infection.

COVID-19 risk levels based on everyday situations.*High frequency of false negatives are prevalent in pre-symptomatic and asymptomatic cases (Dugdale et al., 2020; West et al., 2020; Woloshin et al., 2020). A negative test result should not be viewed as adequate precaution to ensure low risk of infection and transmission. The best precaution remains to avoid any gatherings at all. Minimum exposure times and precautions are obtained from the Center of Disease Control’s definition of close contact.

As we welcome the new year, along with it comes a more contagious variant of SARS-CoV-2. Making its first appearance in the United Kingdom in September, the virus under investigation termed VUI-202012/01 or B.1.1.7 comprises multiple spike protein mutations  (Global Initiative on Sharing All Influenza Data, 2020). The most concerning are the N501Y and 69-70del mutations. The former mutation increases the binding affinity to the ACE2 receptor, basically giving the virus a better fit for the lock-and-key mechanism used to enter our cells.  The latter facilitates viral evasion from the immune system, omitting a critical region the immune system previously used to identify and destroy the virus (Rambaut et al., 2020).

This variant exponentially infected England over the winter, provoking a stricter lockdown. As travel peaks during the holiday season, we see it spread to other countries including the Netherlands (Kupferschmidt, 2020) and the United States (Holcombe & Lauren Mascarenhas, 2020). A similar variant defined by another N501Y mutation surfaced in South Africa where younger people experienced more severe symptoms, but this claim requires more supporting evidence (Kupferschmidt, 2020).

Conclusive data regarding the variant’s lethality and symptom severity are still in the works. Rapid scientific progress has finally yielded vaccines, but it is unclear whether they are effective against the new strain.

This is not the first time we’ve seen variants of the virus and it may not be the last. Despite the unknowns, one thing remains the most effective way to protect ourselves and others: taking the proper precautions as they evolve with new evidence.

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