How Viral Load Affects Severity of the Disease and How to Minimize Viral Load for Maximum Protection
COVID-19 also known as SARS-CoV-2 or Coronavirus disease is a pandemic disease that is affecting people globally. The COVID-19 virus can be transmitted either through direct or indirect contact with respiratory droplets of an infected person. Respiratory droplets with virus particles, known as virion, are produced when an infected person either coughs or sneezes.1 Being within 6 feet of someone who may be infected with the virus or touching a surface with infected person’s droplets may result in an infection. Since the incubation period (the time between exposure to the virus and start of the symptoms) for COVID-19 is between 5-6 days on average and up to 14 days, it is possible that people infected with COVID-19 can transmit the virus well before symptoms develop.
Viral Load & Severity of Symptoms
According to two research papers from The Lancet, there seems to be a high correlation between the viral load and the severity of symptoms2. A viral load is the amount of the virus particles detected in the body. Although age and any pre-existing conditions also play a big role in the severity and outcome of the disease, higher viral load seems to lead to severe symptoms and worse outcome. Infection does not necessarily lead to disease. Infection occurs when the virus enters your body and starts to multiply.3 Different situations also cause varying viral loads that could lead to infection. For instance, a single cough can release about 3,000 droplets at 50 miles per hour which can stay in the air or travel across the room. A single breath releases anywhere from 50 to 5,000 droplets with low velocity that fall to the ground quickly due to gravity. A sneeze releases about 30,000 droplets traveling at around 200 miles per hour, and an infected person’s sneeze or cough could contain as much as 200 million virus particles into the air.4 Also, viral loads are accumulative, meaning a continuous exposure to small viral loads could lead to disease just as much as short exposure to a large viral load.
An infectious dose is the amount of the virus that an individual needs to be exposed to become sick. For COVID-19, researchers do not yet know exactly what the infectious dose is, but it is likely to be a small number due to the high number of cases.5 Infection that leads to disease is dependent on the amount of the exposure to the viral load AND the amount of time of exposure.
Importance of Wearing Masks
Based on the guidance of health organizations and government agencies, wearing a mask is now an important component in preventing or reducing infection as well as limiting the overall spread of the viral disease. With different features of different types of masks available, it is important to understand the types of masks available for protection. These features include but are not limited to the types of fabric or material, liquid repellent attributes, shape and fit of mask, and filters (and number of layers of filters).
Masks with high filtration or filter efficiencies such as N95s, FFP2 and KN95 masks are an effective way to reduce the viral load that you could be exposed to, as minimizing the viral load when exposed to such viral environment is a key to preventing the disease or at least lessening the severity of the disease/symptoms. These masks are tested and proven for filter or filtration efficiency of at least 95%, which means they are effective in filtering out 95% or more of the particles that are 0.3 microns or greater in size.
Another important factor in determining the effectiveness of these masks in filtering out undesirable particles is the Total Inward Leakage. Total Inward Leakage (“TIL”) is the total amount of particles that enters the mask via both filter layers of the masks and any leakages through the face seal6. KN95 is a Chinese standards (GB2626-2006 and GB2626-2019) designation similar to N95 (U.S. - NIOSH-42C FR84), FFP2 (European – EN149-2001), P2 (Australia & New Zealand – AS/NZ 1716:2012), and KF94 (Korea – KMOEL-2017-64). They are similar mainly for the Filter or Filtration Efficiency ratings (95 %+). However, they differ in terms of Total Inward Leakage. Total Inward Leakage is not N95 (U.S.) or NIOSH standards, as TIL depends on many factors such as the facial fit of the specific wearer; however, other standards such as FFP2, P2, KF94 and KN94 do test for TIL, and they allow up to 8% TIL. As of April 2020, the US Food and Drug Administration (FDA) decided to allow KN95 masks to be used in healthcare settings as suitable alternatives for N95 masks. The CDC also stated that the masks are expected to be suitable alternatives to the N95 masks7.
While most N95s have shown TIL of less than 1% due to the tight-fitting, double headband design and therefore, most suitable for high-risk environment such as hospitals, there is an extreme shortage of these masks. Therefore, these U.S. N95 masks should be reserved for healthcare providers and frontline workers.
Comparison to Surgical or Cloth Masks
Due to the current shortage of N95 masks, KN95 masks or other European or Korean alternatives are considered to be a suitable alternative to N95 standard masks, as they are a substantially better alternative compared to surgical masks and masks made out of normal cloths (vs filtering fabric or materials). Surgical masks and masks made out of cloths are more loose fitting and therefore, cause substantial leakage and typically, have 3 or fewer layers for protection (lower Filter or Filtration Efficiency). Surgical masks and cloth masks allow for greater leakage that occurs around the edges of the mask when the user inhales or exhales, which can allow for greater chances of droplets and virus particles to get through.8 Surgical masks and cloth masks, while they are great at preventing an infected person from spreading droplets that contain virus particles, they do not provide adequate protection from viruses and other contaminants due to the lower filter efficiency and the loose fit between the surface of the face mask and the wearer’s face.9
In summary, KN95s and other equivalent alternatives are substantially better than surgical masks due to the fact that (1) Filter/Filtration Efficiency is as good as the U.S. N95s (95%+), and (2) Inward Leakage is a lot less due to the "3D" or "cup" design and tighter ear loops. This is probably the reason why the FDA decided to allow true KN95s to be marketed even to the healthcare providers. It is important to reduce the viral load if exposed to such an environment with masks with high filter efficiency (vs cloth or surgical masks) to protect oneself and others around him or her. It sounds like common sense, but it seems many believe that surgical masks or cloth masks could provide adequate protection, which is not the case. Having said this, if one does not have an access to high-efficiency filtering masks, it is still recommended to wear surgical masks or cloth masks in order to help reduce spread of the virus.
* Note on masks or respirators with valves
While masks or respirators with one or more valves provide added comfort and breathability for the wearers, the valves are designed for a one-way air flow (filters during inhalation but exhaled air is unfiltered). Therefore, these masks do not protect people around the wearer if the wearer is infected. This is an important consideration since a large percentage of the infected have shown to be asymptomatic. Asymptomatic infected people can easily spread the virus based on false security of protection for both the wearer and people around them.
1 WHO Advice on the use of masks in the context of COVID-19 (April 2020)
2 Is 'Viral Load' Key to Understanding Coronavirus's Severity? (Mar 2020)
3 How Infection Works - What You Need to Know About Infectious Disease (2010)
4 The Risks - Know Them - Avoid Them (May 2020)
5 What is viral load and why are so many health workers getting sick? (Mar 2020)
6 Comparison of FFP2, KN95, and N95 Filtering Facepiece Respirator Classes (May 2020)
7 FDA changes course and allows China's KN95 mask to be used in US (April 2020)
8 Infographic - Understanding the Difference, Surgical Mask, N95 Respirator (2020)