Rapid COVID test would be the key to end the pandemic?

The COVID pandemic might enter the late stage due to the low toxicity of new COVID variants, such as the Omicron variant. However, the omicron variant has high transmissibility than other variants. How could we stop the transmission and end the pandemic? Maybe a rapid COVID test could be the solution. Let’s understand why a quick COVID test would be essential.

There are two types of tests, diagnostic tests and antibody tests. Diagnostic tests are usually used to determine if we have an active COVID-19 infection. If tested for positive COVID, we need to take steps, potential treatment, and quarantine to isolate ourselves from others to prevent transmission. On the other hand, an antibody test is measured to determine the antibodies produced from the immune system in response to the COVID virus. It means that we could not use an antibody test to identify active COVID-19 infection. When should we get a COVID test? There are several conditions, you should do a COVID test, either molecular or antigen tests. 1. If you have any COVID symptoms, including fever or chills, cough, shortness of breath (difficulty breathing), fatigue, muscle or body aches, headache, loss of taste or smell, sore throat, congestion, or runny nose, nausea, or vomiting, diarrhea. Even you are fully vaccinated, you should have a COVID test. 2. If you have had close contact with someone who tested positive for COVID-19. The definition of close contact is to stay with a COVID-positive person within 6 feet for more than 15 minutes. 3. If you had any activities that might put you at high risk for COVID-19, such as traveling, attending a significant social event, crowded indoor gathering. Last, sometimes the workplace or school might establish a screening program to maintain a COVID-free environment. Depending on the program regulation, you might need to do the COVID test weekly.

Figure1, the real-time viral RNA replicates through reverse transcription-polymerase chain reaction (RT-PCR), and the cycle threshold (Ct) value is measured. When the Ct value is smaller, the higher the viral RNA is measured.

The diagnostic tests consist of molecular tests and antigen tests. The primary method is nucleic acid amplification tests (NAATs) in the molecular test. Its amplifying methods are divided into two groups, reverse transcription-polymerase chain reaction (RT-PCR), isothermal amplification including nicking endonuclease amplification reaction (NEAR), transcription-mediated amplification (TMA), loop-mediated isothermal amplification (LAMP), helicase-dependent amplification (HDA), clustered regularly interspaced short palindromic repeats (CRISPR), strand displacement amplification (SDA). Both amplifying methods measure the amount of viral RNA in the body, but the isothermal amplification method might shorten the time to get the Ct (cycle threshold) value. What is Ct value? In the RT-PCR, we used the fluorescent probe to measure the total amount of RNA in each cycle, and the number of cycles reaching the threshold is called the Ct value. In other words, when the Ct value is lower, there are more viral RNA to be detected. In current regulations, there is no standard for Ct value in NAATs. In general, the test result would be positive in COVID-19 viral RNA detection when the Ct value is between 35-40. This is why some people might receive a negative COVID test before the international flight but for a test positive after entering the U.S. On the other hands, the antigen test measures the protein from the virus to identify the infection. Usually, the antigen test is less sensitive to the COVID virus detection but has a shorter time to receive the result than NAATs. Here is the summary table to compare the NAATs and antigen tests:

Table1. Comparison between NAATs and antigen tests

The antigen test could provide a quick and cheap result to screen people who have a potential infection in a community, but it might need to repeat the test to confirm the result by NAAT. For example, in a community screening, we should use an antigen test as a rapid COVID test to quickly screen the people who might have contact with the COVID-19 virus. If a person does not have any symptoms of COVID-19, and the result of the antigen test shows positive, then this person needs to do additional NAAT to determine whether this person has COVID-19 or not. If a person has COVID symptoms, and the antigen test result shows negative, this person still needs a NAAT to confirm the infection. If the final result is positive in COVID-19, then quarantine would be required to stop the virus transmission. Also, if there is an outbreak in the community, serial testing should be done every 3-7 days until there are no new COVID-19 cases for 14 days.

Figure 2, the COVID-19 viral RNA accumulates in the infected body while the viral antigen also increases in the body for antigen test. The sensitivity of viral detection is higher by NAATs than antigen tests.

In sum, the COVID-19 pandemic might enter the late stage because the new variant shows a high transmission rate but less toxicity to humans, and what we need to do to prevent any recent outbreak from breaking down the medical system is frequent rapid COVID test to maintain a COVID-free environment. Then we could get back to our normal life soon.

Reference:

  1. the U.S. Centers for Disease Control and Prevenetion, www.cdc.gov
  2. Paul Drain, Rapid Diagnostic Testing for SARS-CoV-2. N Engl J Med 2022; 386:264-272 DOI: 10.1056/NEJMcp2117115

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Jason (Yen-Chun) Lu, All right reserved.

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