Relevance of Post-vaccination Seroservey

Serosurveys involve testing of blood serum of a group of individuals infected by a particular disease. In present times, serosurveys are in discussion for monitoring the trends of the prevalence of coronavirus, also known as SARS-COV-2 infection at the district level. As per the Ministry of Health and Family Welfare, the serosurveys will be conducted by the Indian Council of Medical Research (ICMR) and the National Centre for Disease Control (NCDC) in collaboration with key stakeholders and state Health Departments. Additionally, surveillance concerning flu and serious respiratory cases are being monitored as an expansion to the serosurvey. In the sero-testing, a more focused population-based serosurvey of the low and high-risk groups will be carried out in selected districts. It is aimed at checking community transmission in any part of the country.

Note: As per the statistics, there is no evidence of community transmission in India. Although few cases of large outbreaks in some clusters with the sharp exponential rise in COVID-19 cases had been reported.

How Serosurveys are conducted?

The population is categorized and tested for low risk and high risk for the serosurveys concerning SARS-COV-2.

Low-risk group- outpatient attendees (non-ILI patients) and pregnant women
High-risk group- Health care workers

10 health facilities- 6 public and 4 privates from each district being tested.
Total sample inclusion-

Low-risk group: 200 samples/week and 800 samples/month
High-risk group: 50 samples/week and 200 samples/month

Kit usage- a combination of RT-PCR and ELISA kits

For the serosurvey conduction, a combination of RT-PCR for the throat and nasal swab detection and ELISA antibody kits will be utilized. The results of the sample pooling are only for surveillance purposes and not for the diagnosis of individual patients.
In the ELISA testing, blood samples will be tested for the detection of IgG antibodies, which in subsequent rounds will be replaced by the RT-PCR based testing.

Note: ELISA testing kit to replace rapid antibody testing kits from China

Institute developing ELISA kits in India

The National Institute of Virology in association with Zydus Cadila is developing the ELISA testing kits. With 97% specificity, the ELISA kits expect to play a critical role in surveillance of a population exposed to the infection (the rapid antibody testing kits failed the ICMR quality tests).

UPSC Prelims specific concepts

How ELISA works?

ELISA (Enzyme-linked immunosorbent assay) is a plate-based assay technique. It is designed for the detection and quantification of proteins, peptides, antibodies, and hormones in blood samples.
While testing, an antigen is immobilized to a solid surface and then complexed with an antibody that I slinked to an enzyme.
If the antigen-antibody coagulation happens, the detection is termed as positive for the respective blood sample. Therefore, the most crucial element of the detection strategy is a highly specific antibody-antigen interaction.

How does RT-PCR work?

In RT-PCR, the presence of specific genetic material of any pathogen including virus is detected.
If the pathogen is present, a specific part of the transcribed DNA is amplified and detected in the RT-PCR.
RT-PCR being a highly sensitive technique is one of the reliable methods as it allows to see results almost immediately while the process is ongoing.

Image courtesy: Centre for Health Security

How relevant Post-vaccination Serosurveys are?

Serosurveys help track the long-term efficacy of the COVID-19 vaccines and help plan future phases of the campaign.

Under the reports that some countries have recently struck off the Oxford-AstraZenaca from their list, it is understandable that many people are apprehensive and have raised their concern to vaccination. India, not only one of the biggest manufactures and distributors of the Oxford-AstraZenaca COVID-19 vaccine, ‘Covishield’ but this vaccine is authorized for emergency use. Another emergency use vaccine in India is Bharat Biotech’s ‘Covaxin’.
As of March 8, 2021, in 37 countries there have been 37 reports of blood clots (including 15 events of deep vein thrombosis (DVT) and 22 events of pulmonary embolism) among 17 million people vaccinated with the Covishield.
The side effects following immunization (AEFI) reported in India among the Healthcare workers and senior citizens those about 45 comorbidities. As per estimates, this is 0.020 per cent with an even lower number of 0.00025 per cent requiring hospitalization and no death linked to the vaccination so far in India.

Therefore, carrying out post-vaccination serosurveys are critical due to the huge genetic and nutritional diversity in the country. This holds a greater significance as India has a range of comorbidities (the presence of one or more additional conditions often co-occurring with a primary condition). Hence, based on the information obtained from the serosurveys vaccination campaigns and vaccination drives can be intensified.

Note: The Union Govt. earlier had notified that the people above 45 years with comorbidities and the senior citizens above 60 years will be inoculated in phase II of the immunization drive (which is started from March 1, 2021).

As the COVID-19 cases are rising in India, the serosurveys hold immense significance in the light of the onset of a potential second wave and for carrying out the vaccination drives with focused district-wise vaccinations.