Antibody Testing And Its Scope In Fighting Covid-19

Virologists and medical experts around the world have made themselves busy by researching different mechanisms to combat against Covid-19. Off late media coverage of antibody testing for SARS-CoV-2, has generated high hopes that individuals who are immune to this virus can be identified. So how does antibody testing work? Are immunity passports feasible? Can it be adopted by authorities as an additional tool to diagnostic testing?

Crux of the Matter

What Is Antibody Testing?

Source: ITV

Antibody testing involves screening a sample of blood for tiny protein molecules known as antibodies that have ‘learned’ to respond to a particular pathogen like a virus. T-cells found in antibodies can easily recognize and fight off viruses on being exposed to them and our immune system mounts different responses based on that within seven to 14 days.

In the case of SARS-CoV-2, antiviral antibodies can be found in the blood after infection, but they are also present in the respiratory system, where the virus resides and propagates. So if a doctor finds in a person’s blood antibodies that respond to virus, they can confirm that the person has overcome the infection caused by the novel Coronavirus.

IgM and IgG are antibodies

What Researchers Say?
Researchers and virologists initially stated that deploying antibody tests widely in communities can help monitor the local population and ease the quarantine restrictions accordingly. According to Dr. Jenny Harries, Chief Medical Officer of England, a deeper insight into the number of people that have recovered from SARS-CoV-2 infection could enable specialists to accurately estimate the dynamic and rate of the virus’ spread. This indicated a possibility of freedom of movement for asymptomatic people having their immunity proof in the form of documents or immunity passports.

A medical study yet to be peer-reviewed in France even posted on the medRXiv server about a finding that suggests, even mild cases of coronavirus that don’t require hospital treatment, produce antibodies in 99.4% patients, with the body’s defenses against the virus increasing during the weeks of recovery.

CDC and WHO Cannot Make Up Their Minds?

People who assume that they are immune to a second infection may ignore public health advice. The use of such certificates may, therefore, increase the risks of continued transmission.

World Health Organization

CDC (Centers for Disease Control and Prevention) came under the scanner recently after there was an alleged mix up of numbers from the two completely different kinds of coronavirus test: RT-PCR and antibody tests, which confused medical experts around the globe who are invested in drawing conclusions from the released data and calculating how deadly the disease is.

About Short & Long Term Decisions
Even though antibody testing garnered media popularity with early stage research, many medical officials weren’t supportive of the immunity passports making public health policy decisions. They believe that there is no solid evidence that people have acquired long-term immunity after recovering from SARS-COV-2. Thus even if people’s bodies have produced antibodies in response to past infection, they can get re-infected. The silver lining being that till date, recurrence of the virus has been rare, so short term immunity.

About Prevalence, Sensitivity & Specificity 
In coronavirus diagnosis, test sensitivity is the ability of the test to correctly identify those with the SARS-COV-2 virus (true positive rate), whereas test specificity is the ability of the test to correctly identify those without the virus (true negative rate).

Thus the antibody test has to be sensitive enough not to miss the antibodies if they’re actually present, but specific enough not to accidentally show a positive result. Now the results of testing can go wrong if in the end, it all depends on the prevalence of the virus i.e how common the virus is in the population being tested. Take the two cases below:

Case 1: In a population where the prevalence is 5%, a test with 90% sensitivity and 95% specificity will yield a positive predictive value of 49%. So only less than half of those testing positive in the antibody test will have antibodies.

Case 2: In a population with prevalence exceeding 52%, a positive predictive value greater than 95% will be yielded, then only less than 1 in 20 people testing positive will have a false positive test i.e positive results for individuals that do not have the antibody in reality.

As per Bayes Theorem, lower the prevalence rate of the virus, larger the number of false positives. Therefore, it’s best to use tests with high specificity that are unlikely to throw up high false positives, like RT-PCR diagnosis, the current gold standard in the Covid-19 battle.

Where All Has It Been Approved ?
The U.S. Food and Drug Administration has issued an emergency use authorization for 12 tests, including a combination of lab-based and point-of-care tests, whereas 200 other devices are awaiting approval.

The EU recently validated an antibody test developed by the healthcare and medical device company Abbott Laboratories.Abbott claims that their test has “99.6% specificity and 100% sensitivity for patients tested 14 days after symptoms began,” which would indicate a high level of accuracy.

What’s Happening in India?
Meanwhile, the Indian government in collaboration with the Indian Council of Medical Research is planning to do antibody tests in 69 districts of 21 major states in the country. A survey would be conducted to collect blood samples from 400 randomly selected individuals (one per household) from 10 clusters in each district. Samples from each of these individuals would be tested for the presence of IgG antibodies using ELISA test developed by the National Institute of Virology, Pune, and manufactured by Zydus Cadila.

So to use, or not to use ?
Complete reliance on antibody tests would give the people a false sense of security and make them lenient towards following social distancing and optimum quarantining mechanisms. These tests can instead be used as an additional tool to diagnostic testing to identify true positive coronavirus cases and lower the overall positivity rate by understanding the natural course of the virus.

Medical researchers globally plan to test new groups of participants every few weeks in the coming months to gauge the pandemic’s trajectory in various regions. Once we know more about the tests, evidence based guidelines can be further generated to indicate how to use the findings. 

  • The first use of the term “antibody” occurred in a text by Paul Ehrlich. The term Antikörper (the German word for antibody) appears in the conclusion of his article “Experimental Studies on Immunity”, published in October 1891. In 1908, Paul received the Nobel Prize in Physiology or Medicine for his contributions to immunology.
  • Angel of the West is an outdoor sculpture in Jupiter, Florida, United States. The sculpture was made in 2008 by German sculptor Julian Voss-Andreae. It is based on the antibody structure published by E. Padlan. The antibody is placed into a ring referencing Leonardo da Vinci’s Vitruvian Man thus highlighting the similarity of the antibody and the human body.
  • Oswald Theodore Avery Jr. was a Canadian-American physician and medical researcher. Avery was one of the first molecular biologists and a pioneer in immunochemistry. The Nobel laureate Arne Tiselius said that Avery was the most deserving scientist not to receive the Nobel Prize for his work, though he was nominated for the award throughout the 1930s, 1940s, and 1950s.