HERD IMMUNITY COULD BE EASIER THAN THOUGHT

NEW DELHI: A region can achieve herd immunity against Covid-19 with fewer people than previously estimated, a new study said on Wednesday, but experts cautioned that the humanitarian and medical costs of taking the route continue to remain high, especially in India.

The study, published in the journal Science and conducted by mathematicians from the University of Nottingham and University of Stockholm, categorized people into separate groups reflecting their age and social activity levels.

Their model found that the threshold percentage of population who need to be infected for the chain of transmission to be broken – known as herd immunity – was 43% and not 60%, as thought earlier.

But the scientists warned that the 43% figure should not be interpreted literally as an exact value and instead should be seen as a study of how population differences affect herd immunity.

“Our findings have potential consequences for the current Covid-19 pandemic and the release of lockdown and suggests that individual variation (for example in activity level) is an important feature to include in models that guide policy,” said Professor Frank Ball from the University of Nottingham, one of the authors of the paper.

The scientists flagged two important things. One, that activity level mattered more than age differences and that more socially active individuals were found more likely to get infected and spread the virus.

The second was that herd immunity can be achieved in two ways: by vaccinating enough number of people or if enough people are infected and develop immunity against the disease. “The herd immunity level is lower when immunity is caused by disease spreading than when immunity comes from vaccination,” Bell said.

The study also said the previous figure of 60% assumed that each individual in the population was equally likely to be vaccinated, and hence immune. However, that was not the case if immunity arises as a result of disease spreading in a population.

While publishing the study, Science editor-in-chief Holden Thorp noted that even if the model’s prediction was correct, none of the seroprevalence studies suggested that any country was close to achieving herd immunity. Other experts pointed to a study that showed levels of an antibody found in recovered Covid-19 patients fell sharply in 2-3 months after infection.

THE STUDY SAID THAT

ACTIVITY MATTERED MORE THAN AGE AND MORE SOCIALLY ACTIVE INDIVIDUALS WERE LIKELY TO GET INFECTED