ANTIBODIES & ANTIBODY TESTING IN COVID-19
Antibody response to infections
Antibodies are proteins produced by the human body in response to an infection and help fight it off. They can stay in the blood for months to years and help in countering future attacks by the same infection.
There are 2 main types of antibodies IgM and IgG. As a rule of thumb, in most infections, IgM arrives on the scene first (usually within a week to 10 days) and at least a week later, IgG appears. However, this pattern varies from disease to disease. IgM then slowly peters out while IgG persists for years and can provide future immunity against the causative microorganism.
So, usually detection of IgM indicates that the infection is still in its acute phase and detection of IgG indicates the infection has passed.
Immune response to COVID -19
So far, scientific data suggests that, in COVID-19, antibodies can appear anytime between 5 days to 3 weeks after the onset of symptoms.
In many other viral infections, the quantum and the virulence of the virus in the patients decline by the time antibodies appear. However, in COVID-19, viral shedding is detectable for a few days even after antibodies are seen. Also, unlike other infectious diseases, detection of IgM does not indicate an acute infection and IgG, a past infection. This is because of the variable time of appearance of IgM and IgG in relation to each other in SARS CoV-2 - IgG can appear later, at the same time or earlier than IgM.
Because of this, detection of total antibodies, rather than the subtypes (specifically IgM or IgG) has more significance in a clinical context.
It has also been shown that almost 95-99% COVID-19 positive patients produce varying quantities of antibodies as they recover. Some might take a longer time to produce the antibody.
Whether these antibodies confer an acquired immunity to the patient against future infection is unclear at this moment, although one would like to believe so.
RT-PCR has been the mainstay in the diagnosis of the disease from the beginning. This is a direct diagnostic test and a positive result is confirmatory of the presence of COVID-19 infection. A positive antibody test, on the other hand, is only a surrogate marker of a recent infection. Therefore, ANTIBODY TEST, BY ITSELF CANNOT BE USED FOR DIAGNOSIS OF AN ACTIVE INFECTION.
When used judiciously and in combination, the results of RT-PCR and antibody tests can be of great help in stratification of the population vis-à-vis actively infected population, recently infected but recovered population, and the normal population.
An algorithm based on these considerations is given below as a general guide for the population at large (source: CDC, Atlanta, USA). The reader is encouraged to follow these guidelines and help the healthcare and regulatory authorities in controlling and, if possible, in eradicating this pandemic.
|Viral testing (Testing for current infection – PCR/Antigen)||Positive||Most likely have an active infection|
|Negative||Most likely do not have an active infection|
|Antibody testing (Testing for evidence of past infection)||Positive||Likely had a COVID-19 infection in the past|
|Negative||Likely never had a COVID-19 infection or never developed antibodies to a past COVID-19 infection|
|Both||Viral Positive, Antibody Positive||Most likely have an active infection|
|Viral Positive, Antibody Negative||Most likely have an active infection|
|Viral Negative, Antibody Positive||Likely had and recovered from a COVID-19 infection|
|Viral Negative, Antibody Negative||Likely never had a COVID-19 infection|
Antibody Test For COVID-19 FAQ
What is an antibody?
• An antibody is protein that develops in the body as a normal part of the immune response to many types of infections.
• Our bodies develop antibodies in the days and weeks after being infected.
• Our bodies develop antibodies in the days and weeks after being infected.
Why would a person want to have a COVID-19 antibody test performed?
This test offers a way for a person to know if they have had COVID-19 in the recent past.
What does the COVID-19 antibody test do?
• As mentioned, antibodies are proteins that your body makes to fight an infection. The presence of antibodies indicate that the immune system has seen the virus and begun a reaction against it. These antibodies develop in most patients within one to three weeks after symptoms of COVID-19 begin and remain in the blood after the infection has passed.
• The COVID-19 antibody test detects the presence of these specific antibodies.
Can this test be used to diagnose COVID-19 infection?
NO. This test is not intended to be a diagnostic test. It is intended to identify if a person has contracted COVID-19 in the past.
Does this test correlate with the severity of the disease?
No. In fact, the result may indicate you were infected with the SARS-CoV2 virus even if you showed no symptoms whatsoever. A person who was hospitalized in critical condition and a person who had barely a slight cough could both show antibodies to this virus. It had nothing to do with the severity of the disease.
How are antibody tests performed?
Antibody tests are blood tests that are conducted through a simple blood draw. The blood is then sent to the lab to be inspected for the antibodies.
How long does it take to receive test results?
If a sample is collected in Mumbai, results can be expected within 24 hours.
Who all are eligible to be tested?
ICMR has decreed that the following people are eligible to be tested:
• Immuno-compromised patients: PLHIV, patients on immunosuppressive treatment, TB, SARI, COPD, patients on dialysis to be considered for testing;
• Individuals in containment zones: In identified containment zones and buffer zones where large number/ cluster of cases have been identified as demarcated geographical areas with residential, commercial structures;
• Health Care Workers: Specifically, all doctors including specialists, nursing staff, support staff, sanitary and other staff including the staff at registration, pharmacists, client facing desk clerks etc. Those workers in health care settings who either faces patients (whether known COVID 19 +ve or not), involved in their care or are in environment of potentially shared spaces or handling fomites;
• Security personnel: All security personnel facing the visitors, conducting their security screening, physical checking and thermal screening. This includes CISF personnel involved in security especially of offices;
• Police and paramilitary personnel civil defense & volunteers:previously or going to face in future. Bus conductors, cleaners and helping staff also should be included; police personnel and volunteers involved in duties facing large number of individuals or those coming in contact with potentially infected individuals, fomites or settings/ places;
• Press corps: Press reporters covering field, interviews, press briefings, etc. and support staff;
• Rural, tribal population (after reverse migration): Migrant workers who have travelled back from urban and peri-urban areas to rural, tribal, hard to reach areas in the country as well as natives after coming in contact with returned migrants.
• Industrial workers or labour force: industry workers, daily wagers, migrant workers, temporary travel related workers, hospitality related works, service sector who are in large number or groups and has potential to spread transmission rapidly in workplace settings;
• Farmers, vendors visiting large markets: Farmers, sellers, brokers, purchasing vendors, distributors and other persons including drivers and labor by virtue of visiting crowded places like main markets where large exchange of materials happen between farmers and vendors during purchase and sell of vegetables etc.;
• Staff in municipal bodies: Municipal staff working in areas like sanitation, water supply, electricity, etc. where interactions with citizens is expected; and
• Drivers: Drivers of hospital ambulances, hearse, buses, auto, taxies, etc. who have been on work font faced large number of individual;
Banks, post, couriers, telecom offices: public or private banks, small or large branches of banks and post, telecom offices as well as couriers;
• Shops: Vendors and/ or owners as well as staff working in shops for essential goods, groceries, vegetables, milk, bread, chemists working at pharmacies, eateries and take away restaurants, etc.;
• Air travel related staff: All ground staff, security staff, janitors, sanitation staff, flight captains and crew for domestic and international as well as cargo may be considered; • International operations: All members of overseas operations for evaluation;
• Congregate settings: People staying or working in slums with very high population density with poorly ventilated building, structures. Persons staying in institutional settings like old age homes, orphanage, asylums, shelters for homeless, hostels, etc. may also be considered;
• Prisons: All prisoners with or without symptoms whenever there is a batch transfer or reported symptomatic;
If I presently don’t have COVID-19 symptoms, should I get the test?
The antibody test will tell if your immune system has developed antibodies against COVID-19. Antibodies may produce immunity to viral infections. However, at this time, research has not shown that antibodies produce immunity to COVID-19 or how long they will persist in your body. Research is underway to gain more knowledge about this.
If I have a positive COVID-19 antibody test, am I protected against future infections?
• A positive antibody test means that you have developed an immune response to the COVID-19 virus.
• We aren’t certain yet how much this immune response protects you from future infections.
Are there any other benefits to doing this test?
• The people who can be tested for COVID-19 antibody tests include a large swath of the population. This is part of ICMR’s sero-surveillance. If a large enough number of people are tested, ICMR can then calculate what proportion of the population has contracted the disease in the past and therefore may have immunity against it.
• This test will also become very useful once a vaccine is developed as vaccines also induce an antibody response which can be confirmed by this test.
• Another benefit of antibody testing is that people who've recovered from COVID-19 with detectable antibody levels may be eligible to donate plasma, a part of their blood. This plasma could be used to treat others with severe disease and boost the ability to fight the virus.
When can this test be done?
This test is best performed atleast 2 weeks after the onset of symptoms. The timing and type of antibody test affects accuracy. If you have testing too early in the course of infection, when the immune response is still building up in your body, the test may not detect antibodies
Is social distancing needed if I have antibodies?
• Yes, it is important to continue social distancing, frequent hand washing, respiratory etiquette, and practice proper hygiene since it’s not certain that having antibodies means that you’re immune to subsequent infection from the COVID-19 virus.
• Furthermore, people can transmit viral particles on their hands, face, other areas of the body, and clothes, even if not infected. This can then increase the risk of infection to others.
How much does the COVID-19 antibody test cost?
The COVID-19 antibody test costs INR 950 if blood collection is done at our lab. A home visit for the same will cost INR 1450
Are there health concerns to taking the COVID-19 antibody test?
• There are currently no known medical risks related to taking the COVID-19 antibody test, beyond that typical of a blood draw.
• If you or your family member taking the antibody test has had issues or concerns with blood draws in the past (bruising, bleeding, fainting, etc.), please alert our centre staff or our phlebotomist and they will advise the best course of action.