Is it possible to achieve Covid-19 herd immunity amid rising delta cases? A doctor answers
- A population is said to achieve herd immunity when a large percentage of individuals become immune to a disease. A doctor on whether or not we will get there anytime soon.
Amid the fear of third wave of Covid-19 infection and a surge in Delta cases in Maharashtra, India continues its fight against the deadly infection with all its might as the country's vaccination drive is on in full steam.
According to reports, India on Sunday registered 42,766 new cases of coronavirus disease in the last 24 hours taking the active caseload to 4,10,048 comprising 1.24 per cent of the total infections.
Out of nearly 11 variants of SARS-CoV-2 virus being monitored by WHO, Delta Plus also known as B.1.617.2.1 or AY.1 is on rise in India as well other parts of the world. Towards the end of August, Maharashtra recorded 103 Delta Plus cases. Approximately 65% of the reported cases were amongst the unvaccinated population.
Dr Rahul Pandit, Director-Critical Care, Fortis Hospitals Mumbai & Member-Maharashtra COVID19 Taskforce explains more about how a virus mutates and what is the possibility of achieving herd immunity against it.
What happens when a virus mutates
"The standard process of mutations impacts us when it leads to changes in transmission levels or on treatment. Mutations can have positive, negative, or neutral effects on human health. For example, negative impacts may include clustering of infections, increased transmissibility, ability to escape immunity and infect others who have poor immunity, neutralization escape from monoclonal antibodies, improved binding to lung cells and increased severity of infection. But positive impacts can make the virus becomes non-viable," says Dr Pandit.
How and when will we achieve herd immunity?
"A population is said to achieve herd immunity when a large percentage of individuals become immune to a disease. Based on mathematical calculations, if vaccines could provide a lifelong, fail-safe shield against infection with SARS-CoV-2, it would need to reach 60-72% of people to establish herd immunity. But if vaccines are only 80% effective at preventing infection, 75-90% of people would need to be immunized — a high bar," according to Dr. Pandit.
If a third wave is triggered, a rise in infection rates may pose the toughest challenge yet for the government, owing to the weaker health infrastructure and staff availability. Robust serological surveys can show where the community is in terms of seropositivity, and in a way, low case numbers are an outcome of the spread slowing. However, in the journey towards herd immunity, many other factors determine daily case numbers and daily deaths, including the age and morbidity profile of those affected, he adds.
Can herd immunity reduce the chance of transmissibility?
Experts feel that herd immunity doesn’t mean that people will be immune to the virus but it only reduces the risk of vulnerable people encountering the pathogen.
"However, most herd-immunity calculations don’t consider behaviour changes, interventions, and rules. For instance, if people follow good physical distancing, the R0 (R0, pronounced “R nought,” is a mathematical term that indicates how contagious an infectious disease is) will go down, if they stop following the same after a while, the R0 will go up again. This will change the herd immunity threshold accordingly," says Dr Pandit.
Vaccination is the way forward
Dr. Pandit says until large-scale vaccinations are done, social distancing, face masks, testing, contact tracing, and isolation, will also need to continue.
"History tells us that we have never achieved herd immunity via natural infection concerning a novel virus, and SARS-CoV-2 is no different. Vaccination is therefore paramount," he says.