SARS CoV 2 is an enveloped, single-stranded RNA virus of the family Coronaviridae, genus Beta coronaviruses. SARS CoV 2 is transmitted person-to-person primarily via respiratory droplets, but also indirect transmission through contaminated surfaces is possible. SARS CoV 2 can be isolated from respiratory samples obtained via nasopharyngeal/ oropharyngeal swabs or from sputum. The coronavirus accesses host cells via the angiotensin-converting enzyme 2 (ACE2), which is the most abundant in the lungs.

The body’s immune system produces antibodies - proteins that are critical for fighting and clearing out the virus. The incubation period for coronavirus is thought to range from 2 to 14 days following exposure, with most cases showing symptoms approximately 4 to 5 days after exposure.

Definite COVID 19 diagnosis entails SARS CoV 2 detection by RT PCR method

Anti SARS CoV 2 Test is an immunoassay test for the qualitative detection of antibodies (including IgG) to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS CoV 2).

Seroconversion or recovery is observed after a median of 10 to 13 days after symptom onset for IgM and 12-14 days for IgG and lasts for several months. Levels and chronological order of IgM and IgG antibody appearance are highly variable supporting detection of both antibodies simultaneously.

How does a COVID-19 antibody test work?
COVID 19 Antibody Test, also known as a serological Test, is done after full recovery from COVID-19. Eligibility may vary, depending on the availability of tests. A health care professional takes a blood sample, usually by drawing blood from a vein in the arm. Then the sample is tested to determine whether you’ve developed antibodies against the virus.

What’s the difference between COVID RT-PCR and antibody test?
COVID RT-PCR Nasopharyngeal swab test is the definite diagnosis for SARS CoV 2 infection.
The FDA approved two types of tests for diagnosing COVID Molecular (RT PCR) and Rapid Antigen Test.

• COVID RT-PCR test- This test detects the genetic material of the virus using a lab technique called polymerase chain reaction (PCR). Also called a PCR test, a health care worker collects fluid from a nasal or throat swab or from saliva. COVID Molecular tests are considered very accurate when properly performed by a healthcare professional.
• COVID Antigen Test- This newer COVID-19 test detects certain proteins that are part of the virus. Using a nasal or throat swab to get a fluid sample, a Rapid Antigen Test for COVID can produce results in minutes. Because these tests are faster and available at less expensive cost than molecular tests are, some experts consider antigen tests more practical to use for large numbers of people. A positive COVID 19 antigen test result is considered very accurate, but there's an increased chance of false-negative results - meaning it's possible to be infected with the virus but have negative antigen test results. So Antigen Test for COVID 19 isn’t as sensitive as the molecular/RT-PCR test. Depending on the situation, the doctor may recommend a COVID RT-PCR test to confirm a negative antigen test result.
• The antibody test for COVID helps to find recovery or seroconversion from the virus and done 2 weeks of post symptoms. The timing and type of COVID antibody test affect accuracy. So test ideally done after 2 weeks of infection
• Another benefit of accurate COVID antibody testing is that people who've recovered from COVID-19 may be eligible to donate plasma, a part of their blood.
• The coronavirus antibody test results indicate how many people had COVID-19 and recovered, including those who didn't have symptoms. This aids in determining who might have immunity. It can also help in contact tracing to assess who else is at risk of infection and how far the disease spread. All of this data will help improve strategies to curb the COVID-19 pandemic.
• But the World Health Organization cautions that there's a lack of evidence on whether having antibodies means you're protected against reinfection with COVID-19. The level of immunity and how long immunity lasts are not yet known

Why do we need Corona antibody testing?
Detection of IgG antibodies for SARS-CoV-2 may be useful in the following situations:

• COVID-19 serological survey to understand the proportion of the population exposed to infection with SARS-CoV-2 including asymptomatic individuals. Depending upon the level of seroprevalence of infection, appropriate public health interventions can be planned and implemented for the prevention and control of the disease. Periodic serosurveys are useful to guide the policymakers.
• A Serology survey in high-risk or vulnerable populations (health care workers, frontline workers, immunocompromised individuals, individuals in containment zones, etc) to know who has been infected in the past and has now recovered.