Despite having more coronavirus cases than any other country, America has a testing rate below several countries that have lower per capita rates of the virus.

The slow rollout of testing has crippled us from making more progress and opening up the economy, says Ryan Demmer of the division of epidemiology and community health at the University of Minnesota.

While testing for active infections has much improved since March, tests are still in short supply in some areas around the country. And where tests are readily attainable, results can still take several days.

Now numerous companies are racing to develop rapid at-home tests. Rather than requiring advanced lab equipment for processing, as current tests do, these new ones would use a sample collected at home and, like a pregnancy test, give you a simple positive or negative in less than an hour. (These tests are distinct from the at-home collection kits also being rolled out that require you to send a sample to a lab for processing.)

If these rapid tests prove to be accurate, affordable, and easy to manufacture, they could allow many more Americans to test themselves, even on a regular basis. This could be a huge asset in the fight against the coronavirus, which continues to spread in the US and take thousands of lives a week.

These tools are urgently needed, says Amanda Castel, a doctor and professor of epidemiology at the Milken Institute School of Public Health at George Washington University.

And for the SARS-CoV-2 virus, which causes Covid-19, testing is particularly important, Demmer says, because a lot of the transmission happens from asymptomatic people or presymptomatic people people who dont have any signs of the virus. (In fact, people seem to be most infectious just before they start to have symptoms.)

But there are many caveats to rolling out large-scale, rapid at-home testing for the coronavirus. For example, the results would need to be shared with public health officials to track cases and trace the contacts of people who test positive, and no ones put in place a way to do that yet. And these tests, some of which will likely have lower accuracy than current PCR tests, are also still probably at least a few months away from being available.

For starters, its painfully clear that we need faster, more frequent, and more widely available testing.

The current testing process in the US typically requires a health care worker wearing personal protective equipment (PPE is still in limited supply in some places) to collect a sample. It then needs a lab to analyze it (which takes hours and expensive machines to amplify the genetic signature of the virus). This resource-intensive process has not proved to be scalable to even approach the 500,000 tests per day that experts say the US should be doing at minimum. And the labs processing these tests continue having major backlogs and supply shortages from nasal swabs to the testing machines further hampering wider rollout.

The long waits for results, which still usually take days, have also caused issues.

Before receiving their results, people are advised to self-quarantine just in case. In addition to people not always complying, this lag can also delay identifying the personal contacts of people who are infected.

As Castel, who has studied testing and tracking for HIV infections, notes, Any time you can get someone tested and provide them with their results right then and there, there is an advantage for public health efforts to stop disease transmission. So far, we havent really been able to do this for Covid-19 at any substantial scale.

At best, there are some coronavirus tests that can provide results within a few hours if the test is done on-site (such as at a health care facility that has a testing lab), but their availability is extremely limited. And the accuracy of another test, made by Abbott, which promised answers in less than an hour, has been called into question.

Having a test that people could do without seeing a health care worker in person would also be helpful, saving strain on medical personnel and personal protective equipment.

At-home tests could make it even safer to test people with symptoms while reducing exposure for health care workers, says Emily Toth Martin, an epidemiologist at the University of Michigan School of Public Health. It might also encourage people who are not sure if they are sick to get tested.

In late April, the US Food and Drug Administration began authorizing some at-home collection kits for coronavirus tests; there are now six such kits that have been authorized. These kits let people collect their sample (whether via a nasal swab or saliva) at home before mailing it to a lab. By avoiding a trip to a medical facility to get tested, they can limit spreading the virus if they are infected and reduce their odds of catching it if they are not.

However, these new test collection methods still require lab processing and take several days to receive results. And many are still only available in limited quantities and are being used primarily for front-line health care workers.

We do have technologies that can detect viral particles more quickly and with far less equipment than the mainstream PCR method. In particular, there are two key techniques researchers are currently pursuing.

One method is known as antigen-based testing. These tests look for virus-specific proteins in mucus from nasal swabs and can produce a quick readout, such as a line on a test strip, if the virus is present. (This is in contrast to PCR tests that rely on multiplying genetic material of the virus with expensive machinery and careful laboratory handling before the virus can be detected.)

Antigen testing is already used for rapid tests for strep throat at doctors offices and as part of at-home HIV tests (which also look for antibodies to the virus). The White House has talked up the potential for wide-scale use of these tests, and the FDA authorized the first one in May.

Antigen tests are, however, considered less accurate than the current PCR tests, with some companies estimating their tests miss one in five people who have Covid-19. This might be in part because, unlike the PCR test, it does not multiply the viral particles and so must rely only on the quantity collected in the sample. So they could be especially prone to missing the infection in people who have early infections or who do not collect the sample properly. So some experts suggest these tests would best serve as a quick initial screening; likely cases would then receive a traditional PCR test for confirmation and diagnosis.

Another approach uses CRISPR, the gene-editing technique. It deploys specially designed molecules to find genetic sequences in the SARS-CoV-2 virus and activate compounds to send a signal again, like a line on a test strip if the virus is present. This could be done in about 20 minutes at home. The two most famous scientists in CRISPR technology, Jennifer Doudna of the University of California Berkeley and Feng Zhang of MIT, are each working to bring tests to market that use this process (with Mammoth Biosciences and Sherlock Biosciences, respectively).

Before the pandemic hit, CRISPR technology was already a potential rapid diagnostic tool for other illnesses such as tuberculosis. Results of early studies like the TB one suggest it might have a relatively high accuracy rate, and an early, non-peer-reviewed paper by the researchers at Sherlock Biosciences reports its lab-based CRISPR Covid-19 test has an accuracy similar to PCR tests.

Like the current viral PCR tests, both of these new test types would only look for current infections, not previous ones. Developing a rapid at-home test for previous infection (by looking for coronavirus antibodies) has been less of a priority so far.

I would choose to test for infection at home over a test for antibodies, because it can change decisions that you make that same day to prevent spreading to others, says Toth Martin. For controlling the pandemic, getting accurate viral tests into the hands of people with symptoms has the potential to stop the transmission through a community. That is incredibly valuable.

But just having these tests widely available would not guarantee a slowing of the coronaviruss surge. It would be a convenient way to broaden the availability of tests; however, it needs to be carefully thought out, Castel says. One potential problem with home-based tests is that you could lose the ability to track the virus: who has it and where it is spreading.

Currently, because Covid-19 tests are being run through approved labs, there is a structure in place to collect information about results positive as well as negative ones. This information gets reported to local and state health departments and, ultimately, the federal government. With this data, officials can learn where the virus is and whether its prevalence is increasing or decreasing in certain locations, and know whom to contact to let people whod been exposed to someone infected know they should self-quarantine and maybe seek testing and care.

But if people were able to get quick results from a paper strip at home, there is a real danger of losing this surveillance that is essential to reducing the spread of the virus across the country.

People who tested positive for the virus would need to self-quarantine, and ideally their contacts would need to be traced and notified to also self-isolate. But if theres no doctor, nurse, or health official involved in the process, that tracing and isolation might not happen. Additionally, it would be important for those who receive a positive test result at home to have access to health care, as needed. Without going through a lab or health care system, these messages and connections could easily get lost.

If people were to do their own testing, ideally a procedure would be in place to ensure that the test results get reported to the local health department, Castel says. What exactly this would look like is still not clear. Mammoth Biosciences, which is working on one of the CRISPR tests, has suggested, for example, possibly somehow integrating the test with an app that would report the results anonymously.

And for the patient side, from Castels work on HIV home-based testing, she notes that having a consumer hotline for people to call with questions about taking the test, interpreting their results, and getting connected to health care would also be crucial.

In the rush to get more tests virus-detection tests as well as antibody tests to more people, the FDA has waved through dozens of brand new diagnostics without subjecting them to in-depth scrutiny. Its done so under the Emergency Use Authorization power, which waives the standard, lengthy approval process. The result is that numerous tests have been deployed with sketchy accuracy rates some estimates suggest even current PCR tests might be missing up to a fifth of coronavirus infections (some of this might be due to the tests themselves and some to imperfect collecting and handling methods).

When talking about scaling up a rapid home-based test to potentially the entire country and giving people a tool that, in essence, told them whether or not they were infected (and could infect other people), Demmer says it is imperative these tests be accurate.

These tests have to be good and valid, and I think were a long way from having those, he says. Antigen tests, for example, tend to perform better when looking for bacteria than viruses. And the CRISPR tests are so new, they are still being studied.

The most important area of accuracy would need to be the false-negative rate. A false negative tells a person they dont have the virus when they really do. And in that instance, the person might have a false sense of reassurance and possibly less adherence to social distancing, resulting in further spread of the disease, Castel says.

Demmer agrees. If its going to scale to millions and millions of people, it has to be very close to perfect, to really remove false negatives, he says. (Occasional false positives for infection-detection tests would be less of a setback in controlling the pandemic.) He notes that to ensure this, government regulation of these tests will be essential.

And people taking the test would also need to understand its limitations. It would be important to have a disclaimer to remind users that the test results only reflect someones status for that particular day and time, Castel says. A negative result one day would not guarantee the person would not become infected and infectious in the coming days.

Current health care worker-administered coronavirus tests run about $50 to $100 each. And tests that allow you to collect a sample at home and mail it to a lab cost around $135 to $150.

So although some companies including Ford, Smithfield Foods, and UnitedHealth are starting to test more of their workers as they return to work, these prices make it unrealistic for many businesses to test everyone regularly for an extended period.

Demmer suggests that if new rapid diagnostic tests could approach something closer to $1, they could be deployed virtually everywhere. And many of these rapid tests are looking like they could come in at under $10 each, which would be a vast improvement in making them more accessible.

Demmer acknowledges it might be a pipe dream, but his vision is to have these sorts of rapid tests at every hospital and health clinic and even at the door to every business for employees and customers alike. So if the tests were extremely accurate, a restaurant could conceivably screen everyone and, within several minutes, know whom they could safely allow in. If potential patrons could get screened first, that eliminates the vast majority of your concerns, Demmer says.

Even if rapid tests meet all of these criteria, they are likely still many months away. Of the antigen tests, for example, David Walt, a professor of pathology at Brigham and Womens Hospital, told CNBC that he expects it would probably be four to six months before they would be given FDA authorization.

If and when they do become available, though, he said, I suspect well have pretty good test strips that people will be able to buy like a pack and test themselves every few days or if theyre considering going back to school or work.

As we look ahead to the cold and flu season of the fall and winter, rapid testing could become even more important. I can see these being especially useful in a few months when we might be contending with Covid-19 and other viruses at the same time, Toth Martin says.

And developing rapid at-home tests for these other viruses would be helpful, too, far beyond the pandemic. Id love to see rapid diagnostic tests for all sorts of respiratory viruses, not just SARS-CoV-2, she says. Knowing you have influenza when you thought it might be just a cold could convince you to stay home and not spread it to vulnerable people.

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