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Coronavirus disease 2019 (COVID-19)

In this article, we cover evidence on the novel coronavirus. Restful sleep, stress management, and a diet low in ultraprocessed food are likely to help immune health in general. For COVID-19 specifically, the most efficacious strategies are physical distancing and hygienic practices (handwashing, not touching your eyes/nose/mouth, etc.).

Our evidence-based analysis on coronavirus disease 2019 (covid-19) features 153 unique references to scientific papers.

Research analysis led by and reviewed by Rob Stenstrom, MD, PhD and the Examine team.
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NEW: A free guide to staying healthy (and sane) while stuck indoors

Summary of Coronavirus disease 2019 (COVID-19)

We have four main COVID-19 pages: on mask efficacy, on dangerous myths, on useful outside resources, and on core evidence (the page you’re reading).

See a list of updates to this page.

Table of contents

First, memorize these four things that DEFINITELY help:

1. Wash your hands for at least 20 seconds, frequently throughout the day

One study of restroom locations in a college town suggested that only around 5% of restroom users washed their hands long enough to remove infection-causing germs,[1] despite how essential this is for reducing virus transmission.[2][3][4][5][6] Also, many people don’t completely dry their hands, even though wet hands increase transmission risk.[7] Some people don’t even wash their hands at all after urinating.[8]

Wash your hand thoroughly for at least 20 seconds. That’s about the time it takes to slowly sing the entire “Happy birthday to you” song twice.

What about hand sanitizers? Well, they’re a good adjunct, but not a replacement for handwashing.

  • On the pro side, coronaviruses are among the “enveloped viruses”, which have a lipid coating with spikes that allow easier binding to target tissues. This coating makes coronaviruses more susceptible to soap and disinfectants, including alcohol-based wipes and hand sanitizers.

  • On the con side, while hand sanitizers have some efficacy,[9] less virus is removed than by thorough handwashing. When you wash your hands, not only does the soap help destroy the virus’s lipid bilayer envelope but the friction produced by rubbing your hands and the water pouring over them wash away the grime that harbors unwanted critters.[10][11]

2. Don’t touch your mouth, eyes, or nose

These are the major routes of transmission, when your hands pick up viruses from other hands, doorknobs, and the hundreds of other germy things you touch throughout the week.[12][13][14] When you cough or sneeze, cover your mouth with your inner elbow. If you’re sick, bump up your game and consider using a mask to protect others, since covering your mouth with your hand or inner elbow still allows a lot of respiratory droplets to spread.[15] 

Instructions about masks vary by country. Keep in mind that masks are most useful when worn, not by people who are healthy, but by people who are infected. The problem with the novel coronavirus is that people can be asymptomatic (they can be infected and contagious but never show any symptoms) or presymptomatic (they can be infected and contagious but not show any symptoms yet — one tricky aspect of the novel coronavirus is that its incubation period lasts 5–6 days on average, and up to 14 days).

Therefore, ideally, everyone should wear a mask. The problem is, there’s a global shortage of medical masks right now, so that the American CDC, notably, currently requests that people without symptoms not use facemasks meant for healthcare workers.

Note that the efficacy of various types of non-N95 masks is not known with certainty and can vary by individual (e.g., if the mask is well-fitted or not, or if it makes you touch your face less or more). As of April 26, the American CDC recommends people without symptoms to wear cloth masks and explains how to make, wear, and wash them.

3. Get serious about physical distancing

Physical distancing, the term the World Health Organization uses instead of social distancing, is extremely important. You don’t need research papers to understand this one. Why tempt fate? Follow your local guidelines and err on the side of caution. Better avoid unnecessary physical interactions than become infected.

4. Call your healthcare professional if you think you may be infected

While you won’t know if you have a bad cold, seasonal flu, or COVID-19, your healthcare provider or your local health department may be able to diagnose you if tests are available, and can at least provide informed advice and medical care. Appropriate advice and early care are critical to avoiding worst-case outcomes such as lung damage or death, since a mild cough and fever early in the course of COVID-19 can quickly transition to pneumonia.[16][17]

If you have COVID-19 and don’t call before you visit an emergency room or other healthcare facility, you run the risk of infecting other patients, some of them older or with comorbidities and thus at high risk of becoming very sick if they contract COVID-19.

Most local, state, and national health authorities are in the process of setting up SARS-CoV-2 testing areas that will not expose hospital patients.

Next, learn these four virus-related terms:

1. SARS-CoV-2

The current virus is not called “COVID-19”. COVID-19 is the infectious disease caused by the virus. SARS-CoV-2 is the actual virus; it owes it name to its genetic similarity to the original SARS virus, SARS-CoV. “SARS-CoV-2” is short for “Severe Acute Respiratory Syndrome Coronavirus 2”.

  • COVID-19 is the disease caused by SARS-CoV-2.

  • SARS-CoV-2 is the virus causing COVID-19.

Originally, in China, there were two strains of the SARS-CoV-2 virus, one of which spreads more quickly and was still prevalent (70% of cases) as in late February, though its prevalence seemed to have already decreased (probably as a result of human intervention) since the early stages of the outbreak in Wuhan.[18]

The faster virus is also more aggressive, but symptom severity is highly individual: someone with the more aggressive strain may have mild symptoms while someone with the less aggressive strain may need hospitalization. (Remember that, in the context of COVID-19, “mild symptoms” can vary from very mild to feeling terrible but not requiring hospitalization.) Age plays a role, as do underlying medical conditions, but even healthy young people have been hospitalized. Why? One possible reason is a higher viral load. Another possible reason is genetic: some people may be “naturally” prone to reacting badly to the infection.[19]

Also, keep in mind that viruses — especially RNA viruses like SARS-CoV-2 — keep mutating. In late Februrary, we knew of two strains; by the end of March, we knew of eight strains, though they’re still very similar. (Nextstrain is an open-access website that shows how the various strains have traveled all over the world.)

For more information on the virus’s structure and properties, see the “Sources and Structure” section of our research breakdown.

2. COVID-19

Of the seven diseases coronaviruses can cause in humans, the most severe are MERS, SARS, and COVID-19, caused by MERS-CoV, SARS-CoV, and SARS-CoV-2.[20] The other four human coronaviruses (called HCoV-229E, HCoV-HKU1, HCoV-NL63, and HCoV-OC43) have long been widespread globally; they cause 10–30% of all upper respiratory tract infections in adults.[21]

COVID-19 is alarming because it has a much higher fatality rate than the flu and because its incubation period is quite long (which partly explains why it has spread more widely than previous coronaviruses: people who are already infected can look and feel healthy and so not take any precaution not to spread the virus).[22][23] 

As of late April, the global case fatality rate of COVID-19 is estimated to be in the low single digits,[24][25][26][27][28] so much higher than the case fatality rate of the seasonal flu (<0.1% to 0.2% of cases).[29][30][22][31] Note that the case fatality rates of both COVID-19 and the seasonal flu vary highly depending on location. Also, note that the case fatality rate of COVID-19 may go down as more people are diagnosed with milder cases (or it may go up or stay the same — things can evolve rapidly!).

3. Incubation period

The incubation period of the virus has been reported as 2–14 days, with a median of 5–6 days. One case study suggests that the incubation period could extend out to 24 days.[32][33] That means you can be infected for quite a while and not feel sick. Thus, you should practice healthy sleeping, eating, and hygienic habits (such as frequent, thorough handwashing and other transmission-reducing habits) even if you don’t feel sick.

4. Viral load

If you have a harmful virus in your body, the less the better. The viral load is basically the amount of virus per volume of fluid (such as sputum, the phlegmy stuff at the back of your throat, or blood). For COVID-19, the viral load appears to peak 5–6 days after symptoms start, but even people without symptoms can have a significant viral load, which suggests that the virus can be spread by a person before this person becomes symptomatic.[34] 

The mean viral load of severe cases was around 60 times higher than that of mild cases, suggesting an association between viral load and symptom severity.[35] You can reduce your viral load by minimizing your exposure to the virus, through measures that include avoiding sick people when possible, frequent handwashing lasting at least 20 seconds, and not touching your mouth/nose/eyes.

COVID-19, the disease caused by the SARS-CoV-2 virus, has higher transmissibility and much higher case fatality rate than the flu. Its long incubation period partly explains why it has spread more widely than previous coronaviruses: people who are already infected can look and feel healthy and so not take any precaution not to spread the virus. To protect yourself and others, tried-and-true methods — such as physical distancing and thorough handwashing — are essential.

Our research breakdown has further coverage of recent COVID-19 studies.

Finally — can supplementation or nutrition help you?


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COVID-19 differs from the viruses that cause the flu or the common cold. The viruses that cause the flu are from the family Orthomyxoviridae,[36] while the virus that causes COVID-19 is from an entirely different family: Coronaviridae.[37] As for the common cold, around 50% of cases are caused by rhinoviruses, which aren’t closely related to coronaviruses.[38] And while around 15% of colds are indeed caused by certain types of coronaviruses,[39] the most common of those differ from the virus that causes COVID-19 in various ways[39] (they notably limit themselves to the upper respiratory tract[40]).

Basically, nobody should claim that cold/flu supplements or trials directly apply to COVID-19. While a few supplements — such as echinacea, garlic, and quercetin — have gained popularity on social platforms, evidence for their potential benefit is non-existent for COVID-19 or variable for immune-system support.

For all we know, some supplements could worsen specific manifestations of COVID-19 or interact with potential medications. As always, keep in mind that supplements vary in potency by brand and may have unstudied or understudied dangers.[41][42][43][44][45][46][47]

The immune system is complex and finely balanced. No single supplement (or food) will affect every aspect of it. It does need some micronutrients to function optimally, including:

Of these, iron, vitamin D, and zinc tend to be more frequently underconsumed. Yet, no specific micronutrient is going to work wonders by itself, even if you megadose; but taken together in sufficient amounts — preferably from foods rather than supplements — in the context of an overall healthful lifestyle, they can support immune function (more so if you usually don’t get enough).

⚠️ Caution: Don’t let supplements lure you into a false sense of security

If you opt to supplement with any of the micronutrients mentioned above, remember that none of them have proven efficacy against COVID-19.

Supplements are not strictly necessary, and they pale in comparison to established preventative measures.[48] Maintaining proper hygiene should be your primary focus, as it is the proven option for reducing the risk of spreading or contracting SARS-CoV-2.

If you suspect you have COVID-19, do not rely on supplements as a cure or treatment — contact a healthcare professional.

The International Society for Immunonutrition (ISIN) has published a position statement on nutrition, immunity, and COVID-19. For the elderly specifically, it recommends increasing the daily intake of the following nutrients:

Importantly, they make the following disclaimer:

“There is no specific evidence these nutritional measures can help protect against, or even lessen the effects of, COVID-19 infection.”

Let’s add that the higher end of their zinc intake range (220 mg) far exceeds the established Tolerable Upper Intake Level (UL) of 40 mg/day.[49] Taking too much zinc for too long can be toxic and cause copper deficiency.[50][51] Do not exceed the UL for zinc for more than 2 weeks unless under the direction and supervision of a physician.

🔍 Digging Deeper: Elderberry and cytokine storms

Some people on the Web have warned that elderberry could initiate or exacerbate a cytokine storm, based on a study that shows increased cytokine production from elderberry intake.[52] The authors say that “in addition to its antiviral properties, Sambucol Elderberry Extract and its formulations activate the healthy immune system by increasing inflammatory cytokine production” (cytokines being a natural and critical part of your immune system’s response to pathogens).

A cytokine storm isn’t a mere bump in cytokine production, however, but a severe immune overreaction to a pathogen. In cases of severe flu, cytokine storms are associated with outcomes ranging from lung inflammation to death.[53]

Although it appears unlikely that a low-to-moderate dose of elderberry would initiate a cytokine storm, nobody knows if taking elderberry (especially in large amounts) when symptoms are severe has any adverse effects. Discuss supplementation thoroughly with your physician before using it, as evidence is constantly changing for COVID-19.

Some supplements have evidence for prevention or symptom reduction for the flu or the common cold — nobody knows how well this evidence applies to COVID-19 (if at all). Moreover, supplements vary in potency by brand and may have unstudied or understudied dangers.

Harm from supplementation is especially possible with COVID-19 due to unknowns surrounding this virus and its manifestations, so please primarily rely on good hygiene habits, sufficient sleep, and a healthy diet.

Nutrition and lifestyle interventions

A poor diet is tied to an increase in general infection risk, and lack of sleep is possibly an even greater factor. Yet when it comes to infection prevention and treatment, way more trials look at supplements than at dietary and lifestyle strategies. Don’t be fooled! There’s greater financial incentive to run supplement trials, and they are much cheaper, shorter, and easier to conduct than diet trials.

Moderate evidence for immune function in general:

  • Sleep. If you don’t sleep enough, your immune system is impaired,[54] making you more likely to catch the flu and the common cold.[55] Sleep quality is also important.

  • Less ultraprocessed food. High amounts of processed carbohydrates and refined fats can interfere with proper immune function.[56] Even short-term hyperglycemia can impair your response to infection.[57]

Trials for diet and lifestyle interventions are scarce, because they’re harder and more expensive to conduct than trials for supplements. Getting enough sleep is probably the most critical strategy. It’s likely that a diet high in ultra-processed foods impairs immunity.

Get COVID-19 updates straight to your inbox, based on up-to-date science

There’s a lot of misinformation being spread about the novel coronavirus. Get updates you can trust.

Things to Note

Also Known As

COVID-19, 2019 novel coronavirus disease

Do Not Confuse With

corona, SARS, flu

Caution Notice

This page is not a replacement for information from health authorities! Evidence is constantly evolving. Please use health authorities such as the WHO and CDC as your primary sources of information — they have hundreds of researchers and public-health officials working specifically on reducing the spread and impact of COVID-19.

Click here to see all 153 references.