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The importance of post-vaccination serosurveys

Such studies would help track the long-term efficacy of the Covid-19 vaccines and help plan future phases of the campaign.

Written by Anu Raghunathan |
Updated: March 22, 2021 8:50:57 am
Vaccines are a critical tool in the fight against COVID-19 and are our best bet in this pandemic to reach herd immunity

Indians are increasingly asking the question of whether or not to get vaccinated. Last week, some countries had struck off the Oxford-AstraZeneca vaccine from their list. Though the questions raised about the vaccine have now been answered and its use has resumed, it is understandable that several people may still have apprehensions. Blood clot formations and a potential connection with the COVID vaccine in countries across the EU and beyond was the prime reason behind the pause in the use of this vaccine. India is not only one of the biggest manufacturers/distributors of the Oxford-AstraZeneca COVID-19 vaccine Covishield, but this vaccine is one of the only two authorised for emergency use in India, the other being Bharat Biotech’s Covaxin.

Vaccines are a critical tool in the fight against COVID-19 and are our best bet in this pandemic to reach herd immunity. Covishield is made from another virus of the adenovirus family that has been modified to contain the gene for making a protein from SARS-CoV-2. It does not contain the virus itself and cannot cause the disease. The vaccine teaches the body to recognise the viral protein that allows entry into the body and produce antibodies in a safe and relatively controlled manner. Thus, when the body encounters the real virus, it will be already trained and ready to eliminate it before it can do any damage. The most common side effects have usually been mild or moderate and are known to subside in a few days.

There have been 37 reports of blood clots that include 15 events of deep vein thrombosis (DVT) or thrombocytopenia and 22 events of pulmonary embolism among more than 17 million people vaccinated with the Oxford AstraZeneca vaccine across more than 37 countries as of March 8. These numbers are much lower than what would be expected to occur naturally in a general population of this size and do not seem higher than what would be seen annually in the EU, suggesting that they were coincidental fatalities. The side effects or adverse events following immunisation (AEFI) reported in India where the vaccine rollout has been primarily for health care workers (HCW) and front line workers (FLW) and now senior citizens and those above 45 with comorbidities, has been minimal (0.020 per cent), with an even lower number (0.00025 per cent) requiring hospitalisation. There have also been no deaths linked to the vaccine so far in India. Hence, when it comes to risk, the odds are clearly in favour of vaccination.

The potential benefits of the Oxford AstraZeneca vaccine in preventing COVID-19 outweigh the risks of side effects. The World Health Organisation and the European Medicines Agency (EMA) currently maintain this view. However, due to the undocumented nature of the thromboembolic events in relation to vaccination, this safety signal is currently being reviewed at an accelerated rate by EMA’s Pharmacovigilance Risk Assessment Committee (PRAC).

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In the UK, currently, those above 50 years of age are being vaccinated, while in most of continental Europe the preventive is being administered to those over 70 years of age. If the population in this age group refrains from getting vaccinated and gets infected by SARS CoV2, there is a 10-25 per cent chance of them becoming severely ill and needing hospital care. One consequence of critical COVID illness is blood clots. This suggests a higher risk of mortality by not getting vaccinated.

There is a need to conduct post-vaccination serosurveys of individuals to track the long-term efficacy of the vaccines and unravel the immune response in India. As the nation awaits immunisation at a larger scale, such studies would be critical due to the huge genetic and nutritional diversity in the country and the range of comorbidities that affect the Indian population. The results can provide valuable inputs for planning further phases of the vaccination campaign and will also support further confidence-building measures for the vaccination drive.

The case count in India is rising. In light of the onset of a potential second wave, and the statistics available on fatalities and the benefits of vaccination, the answer to the question should Indians continue to be vaccinated is a resounding “yes”.

This column first appeared in the print edition on March 22, 2021 under the title ‘Completing the cure’. The writer is senior principal scientist, Biological Engineering Unit in the Chemical Engineering and Process Development Division at the CSIR-National Chemical Laboratory, Pune

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