Serosurvey learnings

#GS2 Health and Governance

News info:

  • Since the pandemic began in 2020, the Indian Council of Medical Research (ICMR) conducted three countrywide serosurveys to live the spread of infection thanks to the SARS-CoV-2 virus. 
  • The third one (from December 17-January 8) showed that 21.5% of the population had been exposed to the virus. Up to May 23, India has been ready to fully vaccinate only 3% of the population and only 10.9% had received one dose. 
  • There are indications that the ICMR is unlikely to right away undertake a fourth national serology survey to estimate the extent of exposure to the coronavirus since January this year.

Why are serology surveys important?

  • Serology surveys take blood samples from participants and measure antibodies to see past exposure to the virus. From almost 10 days after being infected, antibodies grow to sizeable numbers in most patients. 
  • As some studies show, they begin to say no after five to 6 months. Researchers are more curious about a category of antibodies called immunoglobulin G (IgG), that persists the longest and latch onto the coronavirus to stop them from proliferating then their longevity and numbers are proxies to immunity against future infection. 
  • Because the SARS-CoV-2 virus is new, there's uncertainty on how long these antibodies actually last. Serology surveys are thus a crude measure of what proportion of a population is probably going to be shielded from a second infection; this will be employed by planners to make a decision on future healthcare capacity and opening up the economy.

How many serology surveys are conducted so far?

  • The ICMR has conducted three national serology surveys since May 2020 and located that the exposure to the virus was several times that reported by confirmed cases. The third serosurvey that measured the spread of infection from December to early January found that 21.5% of India’s adult population and 25% of those between 10-17 years old may are infected. Before that in August-September, it had been 7%, and therefore the first survey, May-June 2020 estimated infection rate at 0.73%. 
  • The ICMR survey spanned 70 districts, across 21 states, that were meant to incorporate high and low prevalence of the infection also because of the spread of the infection in rural and concrete India and enrolled about 28,000 individuals. Subsequent surveys were conducted within the same districts but included those from 10-17 years also as healthcare workers. 
  • There have also been several city-specific surveys in Pune, Delhi, Mumbai, Chennai — sometimes several rounds — to assess spread among various districts. Many of those surveys, a minimum of before the second wave struck, seemed to suggest that over 50% of the population in urban clusters may are exposed to the virus.
Introduction – Serosurvey Tools

Why is that the ICMR unlikely to conduct a fourth serology survey?

  • India’s devastating second wave began around mid-March amidst a vaccination program that prioritized healthcare and front-line workers, and senior citizens. The antibodies that are triggered after a SARS-CoV-2 viral infection are structurally indistinguishable from those after one is vaccinated. 
  • However, studies do show that those vaccinated after being exposed to the virus have much higher levels of antibodies than those vaccinated. increase in the complication of waxing and waning antibody numbers. Dr. Balram Bhargava, Director General, ICMR, told The Hindu, “Serosurveys lose their scientific relevance once vaccination starts within the population.”
  • In theory, it might be possible to regulate this by eliminating those that are vaccinated from the survey. 
  • However, health officials claimed that thanks to the vicious second wave, hospitals and healthcare infrastructure in several districts were overwhelmed by handling the surge in cases. 
  • A serology survey may be a logistically demanding exercise as detailed interviews got to be undertaken with participants, trained phlebotomists need to be available and dedicated laboratories need to earmarked to analyze the blood work. 
  • This is able to require extensive inputs from the districts. aside from the infections, the main target at the regional level should get on vaccination, and by all accounts, India is struggling to stay up with demand. Only 10.9% of the population possesses one dose in spite of nearly 20.4 crore vaccines having been administered. it's quite possible that the ICMR might consider a future survey when things are more amenable.

Can serology surveys reveal quite just exposure?

  • Surveys provide information on the questions they're designed to ask. Tellingly, the second serology survey did point to a rise in infections in rural India.
  • These surveys showed that enormous parts of the country were unexposed to the virus and hence in danger of infection — because the second wave underlined.
  • The specific blood-analysis tests, called assays, are often wont to check if antibodies produced by the body are targeting the spike region of the coronavirus or an inner envelope containing its genetic material called the nucleocapsid. 
  • The antibodies against the spike are believed to be more relevant to preventing future infections and hence a far better proxy for immunity. they will also thus provide inputs for improving vaccines.

Source: The Hindu

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