Seroprevalence : Pros and Cons
COVID-19: What serosurveys suggest and what they hide
WHY IN NEWS:
The results of five serosurveys ; for the prevelance of novel coronavirus (SARS-CoV-2) infections conducted in several parts of India .
SYLLABUS COVERED: GS 3:Health:Diseases
For PRELIMS go through the definitions of Ig immunity , Sero-testing etc .
For MAINS make notes for this issue . This is an important topic for this year Mains 2020 ! Let us dive in !
- Antibodies are specific proteins made in response to infections.
- Antibodies are detected in the blood of people who are tested after infection; they show an immune response to the infection.
- PREVIOUS RECORDS : Antibody test results are especially important for detecting previous infections in people who had few or no symptoms.
- TRACING : The survey includes people who had blood specimens tested for reasons unrelated to COVID-19.
- These samples are compared to percentage changes over time in each area.
- HERD IMMUNITY : Result doesn’t necessarily mean herd immunity.
- INFECTIONS AND DEATH TOLL : What it does mean is that we need to look much more critically at our numbers of infection and the death toll.
SEROSURVEY AND HERD IMMUNITY
- The results for the surveys varied because of the time they were conducted at and their respective sample sizes into account.
- The common interpretation drawn from all them, however, was whether the cities they were conducted in were moving towards herd immunity or not.
Since taking recourse to herd immunity may by and large be fraught with complacency, experts suggest a second surge can lead to a high case load in these areas, something avoided in the first wave.
- The survey in Pune — conducted in five wards of the Pune Municipal Corporation with 1,520 individuals .
- The seroprevalence was found to be 51.5 per cent.
- Researchers looked into the antibody prevalence.
- What proportion of these antibodies were neutralising antibodies is something unknown at the moment.
- These exercises found the presence of IgG antibodies and not actual antibodies that create a protection mechanism against the virus.
- The prevalence of infection indicated the scale to which it may have spread in the city.
- It is prudent to believe a large number of cases are asymptomatic as they were out of the testing net.
The infection spread found through the surveys was not reflected in COVID-19 cases detected through tests.
Seroprevalence : Pros and Cons
UNCOUNTED COVID-19 DEATHS?
- There may be a possibility of the current testing regime missing out on a large number of positive cases and deaths, since the infection was found on such a large scale.
- An improvement in the country’s testing regime was needed.
- A long-term immunity is, thus, also not reflective in such surveys.
- Otherwise you would have started seeing a large number of re-infections by now.
- SAMPLE SIZE : The study has limitations that are associated with both the samples and with the tests used.
- MINIMAL DATA : The specimens were collected for clinical purposes from persons seeking health care and were shared with labs with minimal accompanying data.
- FALSE SENSE OF IMMUNITY : There is currently no evidence to suggest that people who have recovered from COVID-19 are immune to catching it again.
- Representativeness may vary by age group as well.
- ACTIVE INFECTIONS : If you test negative for COVID-19 antibodies, it doesn’t rule out the chance that you could have an active infection and haven’t built up the antibodies against it yet.
- GEOGRAPHICAL LIMITATIONS : Furthermore, at this stage in the pandemic, infections may not be evenly distributed even within these geographic sites.
- ACCURACY : Seroprevalence estimates for large geographic sites may not be accurate if the majority of samples come from specific areas with higher infection rates.
Finally, the representation of specific geographic pockets may not be the same between the 2 commercial laboratories, and underlying patient populations may differ between the laboratories.
- Experts, thus, suggest that the cities are closer to achieving herd immunity, is like jumping the gun.
- A clear message from the surveys is the disease outbreak is widespread .