The country is going through a terrible phase of the second wave of the COVID-19 pandemic. During this phase, more people are getting infected with the virus and we have seen more critical cases requiring medical emergency and oxygen supply surfacing. 

Looking at the condition, the government has been speeding up the vaccination process in the country, and now anyone above the age of 18 years will be eligible to take the jab. On Monday, the Union government announced that the third phase of COVID-19 vaccination in India will begin from May 1 and everyone above the age of 18 years will be eligible to be vaccinated.

The experts are urging people to focus less on efficacy numbers and instead prioritize getting vaccinated with whichever authorized vaccine is being offered to them. But before that, today let us understand what vaccine efficacy means and what is herd immunity?

What is vaccine efficacy?

Vaccine efficacy is the percentage reduction in disease in a group of people who received a vaccination in a clinical trial. It differs from vaccine effectiveness, which measures how well a vaccine works when given to people in the community outside of clinical trials.

Efficacy reflects how well the vaccine works in a controlled setting like a clinical trial. All new vaccines undergo clinical trials to test how well they work.

The developers of a vaccine candidate usually determine the main goals of their trial in their clinical trial study protocol. These goals are called the primary endpoints. 

Scientists can calculate how well a vaccine candidate works by looking at the difference in new cases of the disease between the group receiving a placebo and the group receiving the experimental vaccine. This is called vaccine efficacyTrusted Source. 

There are chances that the efficacy numbers may dip when vaccines or other medical interventions are released into the general population.

What is herd immunity?

The term refers to when enough people become immune to a disease that the virus is unable to transmit to new hosts.

When most of a population is immune to an infectious disease, this provides indirect protection or population immunity (also called herd immunity or herd protection) to those who are not immune to the disease.

Depending on how contagious infection is, usually, 50% to 90% of a population needs immunity before infection rates start to decline. 

The higher the level of immunity, the larger the benefit. This is why it is important to get as many people as possible vaccinated.

The more people who are vaccinated, the less opportunity the virus will have to spread in the population, and the closer we will be to herd immunity.

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