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Vaccines,  the  long and only route to herd immunity

While the World Health Organization is of the view that vaccines are the only shot at achieving herd immunity, two major clinical trials have been temporarily halted following unexplained illnesses. Mint analyses how long the immunization drive would take to materialize.

How do we describe herd immunity?

When a majority of the community is immune to an infectious disease, whether through vaccination or prior illness, it reduces the spread of the disease from one person to another, leading to herd immunity. It is calculated from the reproductive number, or the number of secondary infections caused by one infected person. This, however, varies for every infection type. For covid, experts estimate 70% of the population must be affected for community to reach herd immunity. With a population of about 1.3 billion people, India will have to vaccinate around 900 million people to reach herd immunity.

How has development of vaccine progressed?

Globally, 42 vaccines are undergoing human trials right now, with another 151 in the pre-clinical stage. In India, three vaccines—by Serum Institute of India, Bharat Biotech International and Zydus Cadila—are in human trials, and half a dozen more are in pre-clinical stage. Serum Institute’s candidate is in phase 3 trial, while the other two are in phase 2. At least one candidate is expected to get nod by December-end or early next year, and commercialization may begin by June 2021. While vaccines take at least five years to develop, covid candidates are going through all three phases of trials in a year.

Booster shotHave any of the vaccine trials faced safety concerns?

AstraZeneca’s trial was paused last month, while Johnson & Johnson’s study is also temporarily halted due to an unexplained illness in one participant each. In J&J’s trial, the pause is not a major concern, with no clarity on what caused the illness. For AstraZeneca, all global regulators, except the US FDA, allowed resumption of trials after a thorough review of the safety data.

How will logistics work out post-vaccine?

India has the largest vaccine manufacturing capacity and Serum Institute is the world’s largest producer by volume, with an annual capacity of over 1 billion doses. Bharat Biotech and Zydus Cadila plan to produce at least 200 million and 100 million doses, per year. However, Bharat Biotech and Serum’s vaccines require two doses, while Zydus Cadila’s needs three doses. While India can produce 1 billion syringes per year, about half of it will be for exports. Cold storage and transport are key to India’s immunization plan.

Who will get the covid vaccines first?

WHO and governments worldwide are coming up with guidelines prioritizing people who are at high-risk, including front-line workers such as healthcare executives and the police, besides the elderly and people with comorbidities. On Wednesday, WHO said the young and heathy might have to wait until 2022 to get the covid-19 vaccine. The entire immunization process could take around three years. However, as the clinical trials are short, we will not know how long the vaccines will provide immunity. – Livemint

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