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Your biggest questions about coronavirus, answered

Battling the spread of Covid-19 is going to be a long-haul effort. Here’s what you asked us.
March 19, 2020
Paige Vickers

Here are answers to some of the biggest questions our readers have about the outbreak, which we collected in a survey sent out through social media and other avenues.

This post will stay live with more questions added to it (and, hopefully, some answers) as the outbreak progresses. Get in touch through this Google Form if you have any more questions, and we will do our best to answer them.

Updated: July 14.

Is the virus airborne?

For a while, there was no consensus from scientists about whether coronavirus meets the scientific definition of “airborne.” This was both a semantic problem (health professionals from all walks of life have different criteria for what qualifies as “airborne”), and because of a lack of data (we just didn’t know how long the virus could last in the air, and whether it was still infectious). 

Over time the evidence has grown. Several big studies point to airborne transmission of the virus as a major route for the spread of covid-19. Other studies have suggested the virus can remain in aerosolized droplets for hours. One new study led by researchers at Tulane University shows that infectious aerosolized particles of SARS-CoV-2 could actually linger in the air for up to 16 hours, and maintain infectivity much longer than MERS and SARS-CoV-1 (the other big coronaviruses to emerge this century). 

Given all this, the question now is less about whether airborne transmission is real, and more about how we should respond. If the virus truly is airborne, it means we that sanitizing surfaces is less effective than we thought. Social distancing and mask usage is more paramount, and should be enforced much more aggressively. Ventilation is key to making sure airborne virus particles cannot collect and linger in the air. We have to lean more heavily on technologies that can disinfect whole rooms at once, like UV light. We have to reduce the number of people allowed indoors, and ensure they can get in and out as fast as possible—the longer people spend time indoors, the more airborne virus is able to accumulate in the air. And perhaps most of all, we need to slow down or even delay reopenings in several cases.

What do we know so far about covid-19 immunity?

That’s still a work in progress. We know the body starts to produce antibodies five to 10 days after infection. We know the immune system follows a pretty standard blueprint like it does for most respiratory viruses— an infection that causes severe symptoms is likely to lead to a stronger immune response, which should encourage strong and longer-lasting immunity in the future. On the flip side, a mild or asymptomatic case is likely to yield lower antibody levels, as was found in covid-19 patients in a new study published in Nature Medicine last month.

But it’s not quite clear that antibodies even appear in all cases. A preprint study last month, which measured antibody levels in patients in London, found that between 2% and 8.5% didn’t even develop detectable antibodies. Those in this group who survived infection (typically younger people) likely had to fight off infection through cell-mediated arms of the immune system—white blood cells and cytokines that directly engage and kill pathogens—rather than through antibodies that neutralize the virus. 

We still don’t know how long immunity lasts (could be only a few months), and if it means people could fall prey to repeated infections.  And we’re still not sure what kind of covid-19 immunity we will get from a potential vaccine—whether it’s total or just protection from the worst symptoms. It won’t be until phase III trials (which will directly measure the vaccine’s efficacy) that we'll have a better sense of what the relationship between antibody levels and immunity is, and what sort of immune response a vaccine needs to elicit to provide true protection.

Can blood type affect how susceptible you are?

There is some evidence to suggest there’s a relationship between how severe a covid-19 infection is and what someone’s blood type is. As far back as March, Chinese researchers analyzed blood types in 2,173 infected individuals from Wuhan and Shenzhen, and compared those results with surveys of blood types from healthy populations in the same region. They found that 38 percent of the covid-19 patients had Type A blood, compared to just 31 percent of the healthy people surveyed. By contrast, Type O blood seemed to lead to a reduced risk, with 26 percent of the infected cases versus 34 percent of healthy people. And Type A patients accounted for the largest proportion of covid-related deaths than any other blood type. Another study at Columbia University found similar trends: Type A individuals were 34 percent more likely to test positive for the coronavirus, while having Type O or AB blood individuals had a lower probability of testing positive. 

None of these studies were peer reviewed. But one that was, a genome study published in the New England Journal of Medicine on June 17, looked at genetic data from more than 1,600 hospitalized covid-19 patients in Italy and Spain, comparing their genes to 2,200 uninfected individuals. Those researchers found two gene variants in two regions of the genome associated with a bigger likelihood of severe covid-19 symptoms—including one region that determines blood type. 

Overall, patients with Type A blood had a 45 percent increased risk of experiencing respiratory failure after contracting covid-19, while those with Type O had a 35 percent reduction in risk.

It’s completely unknown yet what would cause this. The authors of the NEJM study hypothesize that the proteins that define Type A and B blood might affect the immune system’s production of antibodies. The genes that determine blood type might have something to do with the ACE2 receptor that the coronavirus uses to infect human cells. 

In any case, blood type doesn’t seem to be among any of the more significant risk factors that distinguish mild cases from severe ones.

How does coronavirus attack the body?

  • The lungs. Covid-19 is a respiratory infection. It typically starts off in the upper respiratory tract (everything above the vocal cords), and moves into the lower tract if the virus isn’t cleared out quickly. When it attacks the lungs, a severe illness can form. Pneumonia and other complications can set in, and it becomes more difficult for the body to breathe and for the rest of the body to get enough oxygen. If the lungs are damaged too much, patients will be put on a ventilator to help them breathe.
  • The blood. There’s mounting evidence the inflammation that arises from a covid-19 infection leads to blood clots that can do serious harm. One of the biggest examples is “happy hypoxia,” which doctors so far suspect is caused by blood clots in the lungs. Many other reports indicate that these clots can affect any number of organs, including the kidneys, blood vessels, intestines, liver, and even the brain. One study from the Netherlands found that up to 38% of critically ill patients suffered from complications related to blood clots. 
  • The brain. The most severe effect the virus might have on the brain is a stroke most probably caused by—you guessed it—blood clots in arteries leading to the brain. This is happening even in young patients. But the virus may also be causing some milder neurological symptoms—most notably a loss of taste and smell. One study found that 65% of those who tested positive for coronavirus reported that phenomenon. Some scientists think it might be a sign the virus can directly affect the nervous system. Other studies out of Wuhan and France have also found neurological symptoms to be prevalent among covid-19 patients.
  • The heart. Besides clot-related complications caused by blockages in blood vessels, covid-19 seems to exacerbate stress to the heart and wear down cardiac muscle through a lack of oxygen if the lungs are struggling, or as a result of inflammation. And some case studies also suggest the virus is able to infect and damage cardiac tissue directly. 
  • The kidneys. Studies from China and Italy early in the outbreak found that about 25 to 27% of hospitalized patients who died experienced injury to their kidneys. Covid-19 patients suffering from pneumonia often seem to experience kidney injury as well. Why this is happening isn’t clear, but the main suspects thus far are blood clots in the vessels leading to the kidneys, overactive inflammation in the body, a lack of oxygen, or a direct viral attack on the kidneys.  
  • The immune system. Some covid-19 patients are hit by what’s called a cytokine storm: the body’s inflammatory response (meant to help clear out infected cells) goes into overdrive and starts attacking healthy tissue and organs, even after the infection has been resolved. Cytokine storms are discussed in depth further down. 

What is a cytokine storm? And why is it killing some covid-19 patients?

Some covid-19 deaths don’t seem to be caused by the virus itself, but rather the immune system’s overreaction to the infection.

When the immune system becomes alerted to an infection, one of the ways it combats the invading pathogens is through cytokines—small proteins that help coordinate the body’s inflammatory response. Inflammation is the body’s natural response against harm, where an army of white blood cells is dispatched to surround the area under attack. That’s what causes the tissue to swell up. 

But inflammation is a generalized response. When cytokines are released at excessive levels, they can activate too many white blood cells that threaten healthy cells and tissue in other parts of the body. The onset of this hyper-inflammation can be rapid and devastating. Even after the immune system has cleared out the disease, the body can  continue to release cytokines, causing further damage to organs. 

Cytokine storms have been observed in other respiratory illnesses, like influenza. And more importantly, they’ve been observed in other coronavirus infections as well, like SARS and MERS. So it’s not much of a surprise to see covid-19 patients afflicted by cytokine storms as well. There are no published numbers in any studies that say how many covid-19 hospitalizations result in a cytokine storm, but one estimate reported in the New York Times suggests it might be as high as 15 percent

The best treatments so far are cytokine-inhibiting drugs. One study suggests early use blood thinners might be useful in tempering cytokine activation and preventing a storm from breaking out.

How can I participate in new treatment and vaccine trials? 

Many institutions around the world send out their own calls for participants for their own trials, so there are many different resources. 

If you live in the US, a useful place to look is the website for the National Institute of Allergy and Infectious Diseases (NIAID), which supports some studies. Those trials, which include vaccine trials, antiviral drug trials, collection of blood serum samples from recovered covid-19 patients, and testing trials, can be found at this page, which is regularly updated. 

You can also look through a much broader list of US clinical trials regarding cover-19 at

Other institutions around the country are looking for participants for a wide array of trials. If you live close to medical school or a hospital with a research arm, chances are good they are a site for a trial of some kind. Get in touch and see if there’s something you’re able to participate in.
Lastly, if you live outside the US, the WHO keeps a registry of international clinical trials in covid-19 research.

How does the virus spread? Can it be in food? 

The coronavirus is spread between people via tiny droplets of fluid, whether that’s through the air or via contaminated surfaces. These droplets can be expelled into the air primarily through coughing or sneezing—hence the reason social distancing measures call for at least 6 feet of space between individuals. 

According to the FDA, there is currently no evidence that coronavirus transmission occurs through food. Keep up with the same steps you normally take to prevent foodborne illnesses. 

How is the coronavirus spread by infected people who have no symptoms? 

According to Harvard Medical School’s Coronavirus Resource Center, people who are infected with coronavirus but not showing symptoms can still spread the virus. Aerosolized droplets containing the virus can still exit the body through breaths and speech and float through the air, infecting healthy individuals. Masks can help prevent the spread of the virus.

Whether asymptomatic cases are the main cause of the spread of the virus is less clear. We don’t yet know how many infected adults are asymptomatic. According to the CDC, of the 3,700 passengers who were on the Diamond Princess cruise ship who tested positive for covid-19, about 46 percent were asymptomatic at the time of testing. Asymptomatic cases and presymptomatic cases (the former never show symptoms, the latter will eventually show symptoms) are contagious, but it’s not yet clear how their contagiousness stacks up against symptomatic cases. This is why social distancing is important for everyone, no matter how healthy someone might seem. 

Why does Germany have a much lower fatality rate than the other EU countries? 

As of April 7, Germany has 107,458 confirmed cases of coronavirus, the fifth of any country in the world. Yet its death tally stands at 1,983, more than five times less than France (which has 110,049 confirmed cases). 

Germany has experienced a stranger outbreak than most other major countries. The New York Times reports that the average age of infected patients is lower in Germany than many other countries, and fatality rates among the young are far lower than they are among the elderly. The average age of infection in Germany is 49; in France, it’s 62.5.

Germany has also been testing people more aggressively than their European counterparts. In the mold of Asian countries like China and South Korea, Germany is testing hundreds of thousands of individuals a week. Patients are identified early, doctors can administer life-saving treatment sooner, and public health officials have been able to spot cases of mild or no symptoms and isolate them before those individuals can infect others. As opposed to the US, where individuals can only get tested if they are symptomatic, Germany has been able to test people who are asymptomatic. Contact tracing has also been an aggressive tool in tracking down potentially sick individuals and testing and isolating them. 

Germany has also done a good job of ensuring that its hospitals and health care facilities could manage cases without being overwhelmed. There’s been no shortage of beds, ventilators, other equipment, or staff. 

Can infections cause permanent effects and complications? 

Yes. Many patients who come down with covid-19 pneumonia experience acute respiratory distress syndrome (ARDS), a form of respiratory failure where the lungs are suddenly overwhelmed by inflammation and unable to deliver oxygen to the body’s vital organs. ARDS has a mortality rate of 30 to 40 percent and is the leading cause of covid-19-related deaths. 

There isn’t a whole lot of literature about what happens if you survive ARDS, but long-term lung damage is a possibility, especially for older individuals. UK doctors report that lung damage sustained by ARDS survivors may take 15 years to heal. Hong Kong doctors told the South China Morning Post that they witnessed some covid-19 survivors see a 20 to 30 percent drop in lung function after recovering from infection. 

If PCR tests are so easily contaminated, how sure are we about the accuracy of the case numbers? Should we be suspicious? 

PCR is a gold standard platform for testing. Even a tiny amount of virus in a patient sample can be found and amplified for detection and testing. That doesn’t mean the test is fool-proof. Yes, the reagents can be easily contaminated—which is precisely what botched the CDC’s initial rollout of coronavirus tests in February. But that’s why there are control tests that are used to ensure the entire platform is running as it should. The problem with the CDC’s February tests were that the negative controls were faulty—which was almost immediately made known. 

There is no real reason to be suspicious of PCR tests for diagnosing coronavirus.It’s probably the most accurate testing platform we have for diagnosing covid-19. 

How does coronavirus affect pregnancy? 

At this time, there is no evidence to suggest being pregnant increases your risk for getting coronavirus, or that your risk of developing severe symptoms increases with pregnancy. According to the CDC, there is no increased risk of miscarriage with covid-19. We don’t have much data on whether SARS-CoV-2 can infect infants, and the limited data we have, according to Harvard Medical School, the vast majority of mothers with covid-19 gave birth to babies who showed no clinical evidence of infection. There is also no evidence of the virus infecting breastmilk. 

Expecting mothers should practice safe hygiene and social distancing at this time, and should also speak with their healthcare providers if they have any specific questions.

Have restrictions and lockdowns prevented flu transmission and deaths as well? 

The 2019-2020 influenza season saw a steady decline in numbers throughout the month of March. According to the CDC, the number of clinical cases testing positive for flu decreased from 24.3 percent at the end of February, to 2.1 percent for the week ending in March 28. 

That’s not exactly surprising, as numbers always tend to decline as we near April. But the drop has been pretty sharp. It’s too early to say whether social distancing measures are responsible and how great of a role they played. Other factors involved include the effectiveness of the vaccine and how many people got it, how infectious the flu was this year, and how rigorously people were tested (and whether the covid-19 pandemic played a role in incentivizing testing). We won’t know for sure until epidemiologists get a chance to look over the data.

Does Covid-19 really cause a loss of smell and taste?

On March 20, scientists with ENT UK, a professional organization representing ear, nose and throat doctors, reported that the loss of smell and taste seemed to be a symptom of coronavirus infections, based on anecdotal reports from colleagues around the world. The authors wrote that it seemed 30 percent of confirmed Covid-19 cases in South Korea experienced anosmia (loss of smell) “as their major presenting symptom in otherwise mild cases.” In Germany, anosmia was reported by two-thirds of Covid-19 patients.

And the truth is, it’s not entirely surprising. Post-viral anosmia is the cause of 40 percent of all cases where someone loses their sense of smell. The ENT UK statement says previously studied coronaviruses cause anosmia in 10 to 15 percent of all infections.

Although it’s a normal part of many viral infections, the reason anosmia is a concern for Covid-19 is because it’s often presenting itself in very mild infections, in the absence of more severe symptoms like fever, coughing and shortness of breath. These are people who aren’t really presenting as ill in any significant way, so they may not be self-isolating themselves as they should. 

But before we jump to conclusions, we need to wait for published data that shows without a doubt anosmia is a symptom of Covid-19. If you’re experiencing a loss of smell and taste these days, it’s not a definitive sign that you have coronavirus. But it might be a sign that you should be extra vigilant about self-isolating, and perhaps seek out a Covid-19 test (if it’s available).

How does this end?

Nobody knows. Epidemiologists at Imperial College London suggest we could see a worst-case scenario of 264 million Americans infected and 2.2 million dead. We also don’t know some important things about the virus, including how many asymptomatic cases there are, making it difficult to plan. 

After the outbreak in Wuhan became public in late December, Chinese authorities began enforcing strict measures on travel and activity designed to stop the spread of the virus as aggressively as possible. It seems to be working: China reported no new cases in Wuhan on March 15. Strict measures are said to have helped reduce the number of new infections in hard-hit places like South Korea as well

Unfortunately, for every South Korea or Singapore, there’s a case like Italy, which did not handle the initial outbreak well and is now reeling from the effects, with the virus spreading incredibly fast and taxing health-care systems well beyond capacity. 

That’s part of the reason we don’t know how this will end—we don’t yet have a system of containing the virus that is universally adhered to around the world. Just last week, the UK was suggesting it would forgo strict mandates on social distancing and isolation, and instead take a slow approach that would allow over 60% of its population to become infected in order to encourage herd immunity. The about-face on this policy may have come too late. 

The pandemic could reach a natural end when it finally spreads to nearly every part of the world and no longer has anywhere else to go. But that would leave an unthinkable number of people dead. We could see a combination of various antiviral treatments being fast-tracked sooner to help treat cases, and continued efforts to help slow the spread and “flatten the curve” (more on that below). But the solution that saves the most lives is a vaccine that provides immunity. That will probably take another 18 months to develop, and there’s no telling yet how effective it might be.

How is a quarantine supposed to work?

The idea behind quarantine is to isolate people who are or may be infected, in order to prevent them from transmitting the illness to others, or to sequester healthy people and make sure they stay healthy. If you restrict someone’s movements beyond the incubation period of the infection, you can isolate new cases as they come up, prevent the spread of infection, and treat those who fall sick.

CDC researcher examined flu cultures

There’s some elasticity in what qualifies as a quarantine. Not being allowed to leave home, or being kept in isolation within a hospital, are pretty strict forms. Sometimes quarantines are not mandatory, but self-imposed by individuals who think they might be sick and doing the right thing by waiting out the incubation period (or recovering from illness) before going out in public again.  

Quarantines are only one of a list of actions that can be taken to increase social distancing and help “flatten the curve”—limit the number of cases at any one time, so the peak caseload is much easier for health-care systems to manage.

How fast can coronavirus mutate?

Mutations are natural to every gene on the planet, including those that are part of viruses. In fact, we can study these mutations in the coronavirus genome itself to see whether outbreaks in a single country are related. 

So far, it appears the rate of mutation in coronavirus is  less than half the rate of eight to 10 times per month for influenza. And more specific numbers will come as researchers spend more time studying the virus.

It’s harder to say how specifically we can use this information. Multiple genetic mutations are required for a virus to evolve into something more virulent or threatening. Current research suggests the two major strains of coronavirus affecting humans differ by just 0.007%. There’s no reason to think a vaccine developed for one won’t work against the other.

If you survive coronavirus once, can you be reinfected?

Italian walking with bicycle
AP Images

There are a few reports so far that individuals who’ve contracted the disease and been cleared of the virus have tested positive again. So far these seem to be extremely rare —in China they seem to account for less than 0.2% of all infections. Other literature shows that scientists have observed persistent infections of coronaviruses in animals

We still don’t know enough about the virus or about how immunity develops after infection to say much about how this might work. Thus far it seems rare enough not to be alarmed about. And most scientists seem to think errors more likely explain why some recovered patients are testing positive. 

What should we expect as spring arrives? Will the warm weather hurt or help our efforts to stop the virus?

A big question scientists are trying to answer is whether coronavirus peaks during the winter and ebbs during the summer, like the flu. If there’s a seasonal aspect to the virus, then it also means we have to plan for levels of infection in the Northern Hemisphere to rise rapidly as autumn sets in.

The answer is unclear. A new study that hasn’t been peer-reviewed yet suggests that 95% of positive cases globally have thus far occurred between -2 and 10 °C, which could indicate greater transmission in cooler climates.

The prospect of seasonality is already influencing how some countries are approaching the problem. The UK’s maligned former strategy to encourage herd immunity assumed in part that the country needed to plan for keeping its health-care system from being overwhelmed by peak caseloads in winter. 

Yet so many different variables can influence transmission. We’ve only known about the virus for a few months and have yet to actually observe what will happen as the seasons change. The virus may just barrel through the summer unimpeded, or it may exhibit stranger behavior in the winter. We need more data to make strong predictions. 

How long are people contagious when they are infected?

The answer depends on the study you read. A recent study by German scientists suggests that people who test positive are most contagious before they’ve started exhibiting symptoms and during the first week that symptoms show up. Symptoms can appear anywhere between two and 14 days after infection. On the plus side, the same study shows that after about eight to 10 days of symptoms, patients were no longer infectious. This seems to show that though the disease is pretty contagious at the onset, the body gets rid of the virus quickly once antibody production turns on (which is typically within six to 12 days). 

Yet another study, however, suggests the virus can endure in the body for a median of 20 days after infection, and as long as 37 days in some cases. 

The rule of thumb being promoted so far is to remain quarantined for 14 days from the moment you develop symptoms. 

What are the core health and medical tools, technologies, and resources we need to handle thousands or tens of thousands of cases in cities and towns around the US? Why haven’t we scaled up production?

One of the biggest concerns facing health-care systems down the road is the availability of medical ventilators for hospitalized patients. Covid-19 is a respiratory disease, and for those severely affected, it's critical to be able to provide oxygen or mechanical help with breathing. The US has only 160,000 ventilators available at the moment—a fraction of what we may need if the virus hits harder. Current business models are just not designed to incentivize this level of manufacturing, though there are efforts to change that right now.

But by far, the biggest immediate need is testing kits. “We have a simple message for all countries: test, test, test,” WHO director general Tedros Adhanom Ghebreyesus said in a press briefing Monday. Unfortunately, the US simply hasn’t been testing enough people, and it’s almost a certainty there are many more infections than cases that have been confirmed. Production is ramping up now thanks to new efforts by private and academic labs, but might be too late. 

Down the road, we’ll also need to figure out how to scale up manufacturing of antiviral treatments or even a viable vaccine. 

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