When should I get a Covid-19 test? Here’s a simple guide.

A year into the largest vaccine rollout in history, the current phase of the Covid-19 pandemic may seem eerily familiar: rising cases, a new variant of the virus, and the looming specter of a winter surge.

But there are ways to soften the blow of the pandemic this winter. The best thing to do is to get vaccinated against Covid-19 if you haven’t already. The next best is to get a booster shot if your last vaccine dose was more than six months ago.

“You gotta get boosted — first thing,” said Alexander Greninger, assistant director of the clinical virology laboratory at University of Washington Medicine.

After that, there is another crucial measure that some Americans have neglected: continued testing. At the peak of coronavirus testing last winter, the US was administering 2 million coronavirus tests a day. But as shots went into arms, those numbers fell by 75 percent to just half a million a day. Many vaccinated people assumed they could stop getting tested even after being exposed to an infection.

However, the immune protection from vaccines wanes over time, and the rise of variants like omicron stand to erode that shielding further. This leaves even vaccinated people at risk of contracting the virus, sometimes without any symptoms, and potentially spreading it to others. Most of these breakthrough infections have been mild, but some vaccinated people have fallen ill and even died from Covid-19.

Testing guidelines can be confusing, and they have changed over time, particularly for people who are vaccinated. So Vox asked four health experts for their hopes and recommendations about testing right now.

They all agreed that as the omicron variant shows up in more countries and US states, testing remains critical for finding Covid-19 cases. Not only can a positive test tell you when to isolate from others, it can help you warn others who may have been exposed, and it can even help scientists catch the next coronavirus variant.

When and how often should you get tested for Covid-19?

The number of tests performed in the US varies widely from day to day, but on average, it’s currently around 1.7 million per day. This is a big improvement from the low over the summer, but scientists say it’s still not enough.

The Centers for Disease Control and Prevention (CDC) has been tweaking its guidelines for testing throughout the pandemic, and recently added more details about Covid-19 testing for travelers. If you want to travel internationally, you’ll likely need to test negative right before you return to the US.

The agency even created a new chatbot to help people sort out when they should take a test. You answer some basic questions about your test results, symptoms, exposures, and it tells you what you should do next.

If you don’t feel like chatting with a bot, or you’re feeling confused and overwhelmed by the evolving guidelines, here are a few factors you should consider.

The type of test

If you are concerned about an active coronavirus infection, it’s key that you take a test that looks for the virus — for example, a rapid antigen test or a PCR test.

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Don’t take a test that looks for antibodies — proteins that help the immune system contain infections — because antibodies take a while to show up after an infection starts, and they can linger long after the virus is cleared.

Rapid antigen tests take only 15 minutes, you can often self-administer them at home, and they’re cheap — currently about $10 per test. They look for proteins made by the coronavirus. “The great thing with the rapid tests is that they save time, you get results immediately, they’re actionable,” said Greninger.

To catch potential infections early, researchers say it’s worth stocking up and keeping some rapid tests on hand, if feasible. That way the test is ready and available as soon as you need it, and you don’t have to go to a store or clinic to get a result.

That said, rapid tests aren’t as accurate as tests that amplify genetic material from the virus, like PCR tests. These genetic tests are very accurate and can detect low levels of the virus, but they can be expensive and they must be processed at laboratories, so it can take days to get results. They’re useful for confirming Covid-19 cases or catching infections in very early stages when the virus is still at low levels.

When to get tested

For the general public, one of the most critical times to get tested is when you start exhibiting symptoms: fever, chills, a runny nose, a loss of taste or smell. That’s true regardless of an individual’s vaccination status.

“If someone has been vaccinated and develops any symptoms, even mild symptoms, they should be tested,” said Davidson Hamer, a professor of global health at Boston University. That’s particularly true for people at risk of severe disease, like older adults.

Without symptoms, it’s worth getting tested if you have been exposed to someone who may have been carrying the virus. Vaccinated people should get tested five to seven days after an exposure, while unvaccinated people should get tested right away and follow up with another test five to seven days later, according to the CDC.

The agency says vaccinated people do not need to quarantine after an exposure, provided that they don’t show any symptoms. People who have had Covid-19 in the past three months also do not need to get tested if they were exposed, according to the CDC.

If you test negative but still have symptoms of Covid-19, your initial test could have been a false negative — particularly if the negative test was a less-accurate rapid test. The CDC recommends continuing to isolate from others and contacting a health care provider to monitor symptoms, and possibly to conduct another test.

The CDC doesn’t have specific guidance for using tests as a preventative measure, particularly for gatherings, but that’s another useful way to deploy tests. Sports leagues like the NFL have successfully used rapid daily tests to limit and contain Covid-19 outbreaks. The same strategy can work for crowded settings like holiday gatherings, weddings, and parties that can spread the coronavirus.

“You can protect family or friends by seeking out who is infected the day of,” Hamer said. “The same goes for public events.”

Ideally, rapid tests would be used close to daily for people in high-exposure settings like clinics, hospitals, nursing homes, and jails. The frequency of testing can help compensate for the lower sensitivity and specificity of rapid tests. But the costs of so many tests can be prohibitive, and there may not be enough to go around.

“I think we could do a lot more with rapid testing in the US,” said Emily Gurley, an epidemiology professor at Johns Hopkins University, in an email. “They, sadly, have not been widely promoted for regular public health use, though they should be.”

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What to do if your Covid-19 test is positive

If a rapid test is positive, the individual should isolate, follow up with a more robust genetic test like PCR, and consult a health care professional if they need medical attention. The earlier you catch an infection, the better: A doctor can give you Covid-19 treatments if the virus is detected quickly. Many treatments are less effective in the late stages of infection.

The CDC currently recommends that people isolate for 10 days after the start of their symptoms or their first positive test, but some researchers want this recommendation to change, so that vaccinated people can test out of quarantine if a negative result follows a positive one.

Depending on your jurisdiction, public health officials may also ask you about your recent close contacts so that other potentially exposed people can get tested. If they don’t, you should consider notifying everyone you’ve been in close contact with recently, so they can get tested too.

So far, the rise of the omicron variant doesn’t change this guidance. While antigen tests could be less sensitive to the mutations in omicron and miss some infections, the genetic tests may have a better chance of catching variants, though they too could suffer diminished accuracy.

Ramping up testing could help keep omicron in check

It’s good news that 60 percent of the United States is now fully vaccinated against Covid-19, and there are multiple effective treatments for those who do get sick. But with the mutations in omicron, the virus may still have more surprises in store.

While most Covid-19 tests don’t distinguish between variants, they can still provide a lot of useful data — especially during the spread of a variant that seems more transmissible, like omicron. A change in patterns of test results can be an early warning sign that the virus itself has changed.

But tests can only improve public health if officials have easy access to the results and the public acts on them. If people with positive tests continue with their normal lives, they could infect others and worsen the pandemic. And if there’s no contact tracing, other potentially infected people may not even know that they should get tested.

Unfortunately, the US still lacks a consistent national Covid-19 tracking system. State and local health departments provide most Covid-19 test results to the CDC, but they don’t all conduct tests with the same frequency or process tests at the same rate. That leads to a spotty and delayed picture of the pandemic across the country. In turn, health officials have a harder time marshaling resources like vaccines and treatments to afflicted areas or anticipating potential strains on hospital capacity.

The US also has no centralized reporting system for at-home tests, so even as more people take these tests, the information they provide may not do much to resolve the overall picture.

One area where the US has made progress is in genetic surveillance. Laboratories across the country have increased their capacity to sequence genomes from positive test results. Looking at the genetic makeup of SARS-CoV-2, the virus that causes Covid-19, can reveal new mutations as they emerge and hint at the potential damage they could cause.

The US should aim to sequence the genomes of 5 to 10 percent of positive Covid-19 cases, according to Bronwyn MacInnis, director of pathogen genomic surveillance at the Broad Institute. “Although there is a decline in the level of testing recently, we don’t need to sequence every case to have a very good picture of what’s out there,” she said.

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To get the clearest picture of how variants like omicron are changing the course of the pandemic, scientists need to make sure they’re getting a representative sample from across the country, not just in areas with medical research laboratories nearby. Researchers like MacInnis are working on sequencing genomes from harder-to-reach parts of the country to find out what’s driving Covid-19 outbreaks wherever they happen.

Even with a growing variety of testing options on the market, there are still limited supplies of some tests. The Biden administration recently announced that it is paying nearly $2 billion for 280 million rapid Covid-19 tests. The White House also said that major retailers will sell rapid tests at cost, that they will be covered by Medicaid enrollees, and that free testing will be available to anyone at 10,000 pharmacies.

Starting in January, health insurance companies will also be required to cover the costs of Covid-19 tests. But many Americans don’t know how to navigate this process, and that could dissuade people from finding out whether or not they’re infected.

Even as Covid-19 cases are rising in many parts of the country, state and city governments are reluctant to restrict gatherings or mandate vaccines, masks, and tests. The will to implement aggressive Covid-19 containment measures is fading.

But researchers say that many pandemic best practices are still effective: social distancing, good ventilation, face masks, hand washing, and of course regular testing.

“The best tools for omicron remain the same as for previous variants,” Gurley said.