How can you know which strain of Covid-19 you have been infected with?

Experts explain what the symptoms of Omicron are, how to differentiate the variants of Covid and why it is more difficult to distinguish them than it seems.

The Omicron variant of COVID-19 (these are its 8 most recognizable symptoms ) has quickly become the second dominant strain of the virus in Spain, behind the Delta. But given the new wave of cases that we are facing right now in the country, it is expected that the Omicron strain will continue to increase its numbers: it has gone from 3.4% to 47.2% of those infected in just one week.

In countries like the United States, Ómicron has just unseated the Delta variant as the dominant strain of SARS-CoV-2, the virus that causes COVID-19, with more than 73% of cases in the country.

Given the names of the new strains, if you are diagnosed with COVID-19, it is more than understandable that you want to know which one you have been infected with . Although doctors say it's not easy information to come by—even for them—there may be a way to find out. How do you know what strain you have?

How do public health professionals know which strains people have?

"When the Centers for Disease Control and Prevention (CDC) publishes information on the percentages of variants, they are not looking at all the positive tests in the country to get those numbers," explains Dr. Thomas Russo, professor and chief of infectious diseases from the University at Buffalo, to our colleagues at Prevention .

Instead, the CDC conducts genetic sequencing of a percentage of positive tests across the country. For the United States, for example, to get the latest results, the CDC looked at 160 test results from Alabama, 4,157 from Arizona, 18,424 from California, and so on, to get a breakdown of what percentage of those positive tests matched. with a particular strain of COVID-19. And something similar happens in Spain.

CDC officials and lab technicians don't even know whose test results they're analyzing for privacy reasons. These are disidentified before performing the tests, eliminating the name of the person to whom it belongs. "Consequently, the CDC could not call you or your doctor to say what strain of COVID-19 you have, even if they had the necessary personnel to do so, since they do not know it themselves," Russo says.

Does your GP know which strain of COVID you have?

Usually not, and there are reasons for it. "The tests that doctors do in offices and hospitals don't sequence or specify the variant," says Dr. Amesh A. Adalja, an infectious disease expert and scholar at the Johns Hopkins Center for Health Security. " Rapid antigen tests are usually limited to saying whether the test result is positive or negative, nothing more."

Even a PCR test, considered the most reliable diagnosis, "is not going to tell you what strain you have or sequence the test," says Adalja. PCR tests can also take days to give results, which is why now, given the flood of cases, health professionals are opting for rapid antigen tests," explains Russo. The important thing is to detect and stop infections, regardless of whatever strain it is.

So is there a way to tell which strain you have?

This is where things get a bit complicated. The Omicron variant has a particular genetic sequence that can show up differently in PCR test results, a sequence that would not be seen with other strains of COVID-19, such as Delta. "It's called S gene target miss and it can show up as a 'missing band' in the test results," Russo says.

"This may give a clue that it is Omicron, but it is still not definitive," says Adalja. She also points out that most GPs aren't going to ask about the type of strain you have: "They usually just want to know if you're positive or negative. It's more like something infectious disease experts and microbiologists would ask." Still, he says, if you want to know and your doctor gives you a PCR test – and he knows that information – “ you can ask him if there is a miss in the S gene target . If there is, for all intents and purposes, you have the Omicron ".

However, there is a small caveat with all of this: Russo points out that not all Omicron cases show up with a miss in the target of the S gene when doing the PCR. "We're still trying to understand why that is," he says. Therefore, it is possible to get Omicron and not be detected in the result of the PCR test, or simply be infected with the Delta strain."

Can COVID strains be identified by their symptoms?

It won't be an easy diagnosis, "but there may be some indication that you have one variant or another , depending on your COVID-19 symptoms and your vaccination status," says Russo.

"If you're fully vaccinated, it's been at least two weeks since you got your booster shot, and you're still getting COVID-19, the odds are high that you have the Omicron variant," he explains. "Statistically speaking, you're more likely to get infected with Omicron than Delta anyway," she says. "But this theory is reinforced if you have been vaccinated, since Omicron seems to be more resistant to vaccination."

According to a recent CDC study, those symptoms can include:

• Cough
• Fatigue
• Congestion
• mucus

But if you haven't been vaccinated against COVID-19, Omicron and Delta are likely to have similar symptoms:

• Fever or chills
• Cough Shortness of breath or difficulty breathing
• Fatigue
• Muscle or body pain
• Headache
• Loss of taste or smell
• Throat pain
• Congestion or mucus
• nausea or vomiting
• Diarrhea

How important is it to know the strain of COVID you have?

"For the average-risk patient, it really doesn't matter," says Dr. Russo. "At the end of the day, if you're infected, you should go ahead and watch for more serious symptoms, like shortness of breath, and see a doctor regardless." whether you are infected with Delta or Omicron," he explains. "For healthcare professionals, the symptoms and severity of the disease are often what determine treatment."

However, there's an exception. "Certain monoclonal antibody treatments don't work against Omicron ," says Adalja. "From a clinical standpoint, it's important for someone at high risk to know that information."

Still, "getting that information in a timely manner can be challenging, unless the diagnosis was by PCR and the S gene target was missed and that information is readily available to the provider," Russo says. .

In general, doctors say it 's not vital for you or most other COVID-19 patients to know what strain of the virus you have . However, it doesn't hurt to ask.