Start by doing what’s necessary; then do what’s possible; and suddenly you are doing the impossible.– Francis of Assisi
“Can antibody tests help tackle COVID-19?“
SOURCES: THE HINDU EDITORIAL/EDITORIALS FOR UPSC CSE MAINS 2020
Can antibody tests help tackle COVID-19?
Why have States complained about the tests being inaccurate in many cases? And, should India use both RT-PCR and antibody tests?
SYLLABUS COVERED: GS 3:Diseases
- The rapid testing kits that State governments had been using to detect antibodies to the novel coronavirus were throwing up unreliable results.
- In Rajasthan for example, rapid testing kits failed to detect antibodies even when the laboratories had confirmed patients to be COVID-19 positive.
DIFFERENCE BETWEEN RAPID ANTIBODY TESTS AND THE RT-PCR TESTS?
- There are two ways to detect the presence of a virus, directly or indirectly.
INDIRECT TEST :
- Antibody tests, also called serological tests, have usually been the time-tested approach to finding out the presence of a virus in the body.
- It is an indirect test because it cannot find the virus, but it can determine if the immune system has encountered it.
- Antibodies can show up between nine to 28 days after an infection has set in; by that time, an infected person, if not isolated, can spread the disease.
- Sometimes the antibodies may be produced in response to a closely-related pathogen and sometimes they may not be the right kind to counter the infection.
- These are the factors that can make an antibody test erroneous.
DIRECT TEST :
- In an RT-PCR test, a nasal or throat swab is taken from a patient suspected of having the disease.
- The only way such tests turn negative is if the actual sample does not have the virus or the swab was not properly administered and too little of the virus was gleaned.
- This is why it was possible to prepare accurate tests to detect the virus relatively quickly, almost in the middle of a pandemic, and the RT-PCR tests began to be followed as the ‘gold standard’ in detecting the virus.
- As not enough research hours have been spent studying the antibodies and the profile of recovered patients, the antibody tests we have for COVID-19 are imperfect.
WHY IS THERE A CLAMOUR FOR ANTIBODY KITS?
- Antibody tests are fast and relatively inexpensive.
- And at least a minimum of 30 samples are needed to make the process economically viable.
- The tests are done in batches and it can take up to four hours to confidently test for the presence of a virus from a batch.
- If one adds the time taken to isolate the RNA from swabs, this could again take a couple of hours.
- The scale of logistics involved can mean that it can practically take a day for results from a sample to be known.
- It can cost at least ₹4,500 depending on whether one is tested at a public or privately-run facility.
- Antibody tests are portable, can be administered on-site, conducted on masse and give quick answers.
WHAT DO ANTIBODY TESTS REVEAL?
- Given that they are not useful for directly detecting the presence of the virus, antibody tests can be used to gauge the extent of infection in a community or a large group of people who may have had exposure to the virus.
- Much like pregnancy detection kits, rapid-test kits change colour when particular molecules are detected.
- In response to an infection, the IgM is first produced within a week of infection.
- Two weeks later, the levels of IgM reduce and are replaced by IgG.
- The latter is a longer-lasting antibody .
- Antibodies to the chickenpox virus last for decades.
- Those to influenza viruses and even other coronaviruses (that cause the common cold) last no more than a year or two.
- This is why people need flu shots at regular intervals, and one of the reasons why it is practically pointless to have a vaccine for the common cold.
- Rapid antibody tests can also play a role in determining the degree of “herd immunity” in a population.
WHAT HAPPENED TO INDIA’S RAPID TESTING PLAN?
- Another feature of the kits is their sensitivity (in percentage terms, the times the tests correctly identify people as positive for an infection) and specificity (in percentage terms, the times the test correctly rules out those not carrying the virus).
- Specificity refers to its ability to accurately distinguish between the target virus and other viruses.
- Several of these were to be given to States and some were for the ICMR’s own use.
- A first batch from China was deployed in some States and soon complaints began pouring in over inaccurate results.
- After two days, the ICMR advised States to stop using the kits altogether.