Which test for COVID-19 is better? How effective are rapid tests? Will quality tests stop the pandemic?
Fast, accurate and cheap COVID-19 test will make the world a better place
Conducting mass tests for the SARS-CoV-2 coronavirus, followed by quarantine for those infected, is currently one of the important measures to combat COVID-19. Back in March 2020, the World Health Organization called on: “Test, test and test.”
About 40% of those infected with coronavirus do not no symptoms, but they can infect others. Patients who develop symptoms of COVID-19 begin shedding the virus two days before they appear. The sooner the virus is detected in such patients, there are fewer people they can infect.
“Rapid and frequent testing has the potential to make a difference before vaccines are available. The social restrictions associated with infection could have been eased much earlier. ” quotes JAMA Rochelle Walensky, an infectious disease specialist at Massachusetts General Hospital, an advisor to a non-profit organization Rapid Tests.
Michael Mina, epidemiologist at the School of Public Health. T.H. Chana, considersthat the test should cost no more than one dollar. In this case, people could regularly check themselves and self-isolate if a virus is detected.
Why the PCR test hasn’t saved the world yet
Currently, PCR tests remain the most sensitive to coronavirus. In South Korea and New Zealand, their widespread use has helped suppress the infection, indicates author of a publication in Nature. However, this success has not been replicated elsewhere. According to the same article, their effective use was not achieved in the United States due to poor coordination, batches of poor-quality tests and difficulties with supplies.
The efficiency of the PCR test is not great, at best it will take several hours, in real life, in case of a bad scenario, the results can be expected for several days. Hypothetically, a person whose PCR reaction did not detect a coronavirus may already be infected at the time of the test result. The analysis requires a special laboratory and trained specialists, that is, it is resource-intensive.
The relatively high price of the test also complicates mass testing. In Moscow, holding it at home can cost more than 5,000 rubles.
Will antigen tests save the world?
Tests that detect coronavirus antigens (proteins on its surface) are much faster: the result can be obtained within 5-15 minutes. To carry them out, a swab is taken from the nose or from the back of the throat.
Sensitivity and specificity
Antigen tests possess high specificity: according to the American Centers for Disease Control and Prevention (CDC), it aims for 100%. This means that positive results from this test can be taken with confidence, false positives are rare. But its sensitivity ranges from 84% to 97.6%, that is, lower than that of the PCR test. The lower the sensitivity, the higher the risk of a false negative result. The US Food and Drug Administration (FDA) recommends check negative antigen test results in people with COVID-19 symptoms using a PCR test.
Rapid antigen tests have received bad press recently. Wall Street Journal in an article headline tied up them with a COVID-19 outbreak after being taken in the White House Rose Garden. One of the cases was US President Donald Trump. Participants were reported to undergo rapid analysis using the Abbot BinaxNOW test system immediately prior to the event.
Antigen tests have undeniable advantages. They do not require a special laboratory, they are cheaper than PCR. They can be used directly at the bedside of a large (for example, in the emergency room or at home). They can potentially be used in educational institutions and at various events.
Antigen test is not a dream test yet
The high risk of a false negative result and the need for testing are not all disadvantages of an antigen test. There are other reasons why existing test platforms are not suitable for the role of “folk” test, which can be done quickly at home before going to work.
- Available antigen tests are not for independent use. To carry them out, you still need a health worker.
- They are not cheap enough for frequent use. Abbott Test Kit worth $ 5, Quidel – $ 23. The Beckton Dickinson test platform requires a dedicated analyzer that costs $ 250-300. In Moscow, conducting a test in a laboratory can cost about 3 thousand rubles.
- The reliability of existing antigen tests for asymptomatic COVID-19 is unknown. In the latest Cochrane Commonwealth survey, such data are completely absent… The FDA currently recommends that antigen tests only be performed on people with symptoms. For example, the “illustrious” test by Abbott intended for use during the first week of illness.
JAMA gives an example failures use of antigen test in nursing homes in Nevada. Half of the positive tests rechecked by PCR were false positives.
The test can be useful without sensitivity 100%
At the end of July, Walenski and his colleagues published a study that showed that an antigen test with a sensitivity of 70% can also be useful. According to the calculations of scientists, if you check college students with such a test every two days, then the educational institution can be opened against the backdrop of a pandemic. Along with this, standard preventive measures are required (washing hands, wearing masks, and others).
“I would prefer a 90% test over a 70% test, all other things being equal. But other circumstances are not equal. We must distinguish between the strengths and weaknesses of different tests, “- indicates Walenski. She suggests that false negative test results may indicate that the person is no longer contagious. But there is no scientific evidence for this.
Hope is pinned on antigen tests
“We believe that antigen tests have the highest potential for screening asymptomatic people.” considers Mara Aspinall, creator of the Biomedical Diagnostics Program at Arizona State University. She reported JAMAthat now two dozen companies are working on a simple and quick test for SARS-CoV-2, which, in its simplicity, can be compared to a pregnancy test.
“We take a state-of-the-art lab and shrink it down to the size of a plastic-coated strip,” said JAMA Bobby Brooke is the founder of E25Bio, one of the companies that are in the race for a simple test.
A quick test is not a panacea
If there is a rapid test available, it is important that people do not ignore the results. If the infected do not follow the quarantine en masse, there will be no effect. In addition, the passed test is not protection against infection. A person who neglects the standard rules of prevention COVID-19, even an instant test with 100% sensitivity and specificity will not save you from infection. Read about the prevention of a new coronavirus infection in our material.