ADVERTISEMENTREMOVE AD

Does High Seropositivity Mean We Have Achieved Herd Immunity?

Updated
story-hero-img
i
Aa
Aa
Small
Aa
Medium
Aa
Large

Recently, two serosurveys - one on Delhi and one on India as a whole - have given rise to many questions on the state of COVID in India.

A quick recap:

The fifth round of seroprevalence survey conducted in Delhi showed that 56 per cent of the people who were surveyed have developed antibodies against COVID-19, said Delhi Health Minister Satyendar Jain.

Meanwhile, according to the Indian Council of Medical Research (ICMR) nation-wide survey, Indians above 18 have overall 21.4 per cent seropositivity. The survey was conducted between 17 December to 8 January, with blood samples from 28,589 individuals and another group of 7,171 healthcare workers tested from 70 districts across 21 states and UTs.

The survey estimated the average infection prevalence at about 25 per cent in India. While healthcare workers have the highest seroprevalence at 25.7 per cent, ICMR Director General Balram Bhargava announced in a press briefing on Thursday that a large proportion of our country still remains vulnerable and so preventive measures and vaccines are vital.

Have we achieved the famed ‘herd immunity’? Do we still need vaccines? Delhi showed high seropositivity but India showed that a large population was still vulnerable to COVID-19.

Virologist Dr Shadid Jameel explains, “While the Delhi serosurvey does show a good seropositivity rate, we don’t know at what percentage everyone develops what everyone is calling ‘herd immunity,’ although herd immunity is a concept developed for vaccination, not infections.” He jokes that “herd immunity is like herd mentality almost where no one really understands what it means.”

“Yes, Delhi may have 50 per cent exposed to the virus, but what about the other 50 per cent? They will also be travelling and potentially infecting other parts of the country. So vaccines are very important.”
Dr Shahid Jameel, virologist and Director, Trivedi School of Biosciences at Ashoka University
ADVERTISEMENTREMOVE AD

Why Exactly Are Vaccines Important?

In a pandemic, a vaccine does three things:

  1. It protects people who are giving care to others such as the healthcare workers and frontliners who are in frequent contact with other people like the police, public transport drivers etc.
  2. The second purpose of a vaccine is to reduce mortality. And that can be done by vaccinating people who are at a high-risk group, which in India is people above 50 years and those below 50 who have other morbidities.
  3. The third thing a vaccine should do is break transmission to end the pandemic.
“We don’t know at what per cent herd immunity will kick in. Whether it is 50 per cent or 60 like some are saying, we don’t know. So the idea that we don’t need vaccines since we have 50 per cent seropositivity in Delhi is totally rubbish.”
Dr Shahid Jameel, virologist and Director, Trivedi School of Biosciences at Ashoka University

Dr Jameel adds, “Another thing is that all over the world we are seeing mutants are developing. Whatever we know so far say that the vaccines are working on mutants but not as well, which essentially means that even if you get a mutant, you get infected but the severity of the disease will be reduced. This is still a good enough reason to take the vaccine anyway.”

Since vaccines are already available, Dr Jameel says that we must take them as the upsides outweigh any potential risks.

What Is the Relationship Between Serosurveys and Vaccines?

“See, if enough people have developed immunity in a cluster, then those who have not developed immunity are also protected. That’s the concept of herd immunity. But we don’t know when this occurs or at what percentage of people have to develop immunity.”
Dr Shahid Jameel, virologist and Director, Trivedi School of Biosciences at Ashoka University

He adds, “ For example, in measles we know 95 per cent people have to be immunised before the remaining 5 per cent are protected as per the World Health Organisation.” This percentage of people who need to be immune to achieve herd immunity varies for each disease and the percentage is not known for COVID-19.

“The proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known.”
World Health Organisation

Dr Jameel explains that we need more detailed sero surveys, as an average for the whole country will not tell us much. “Say the number is 60 per cent, now I could achieve 60 per cent herd immunity for the whole country through an average where some states have 100 per cent immunity and some have 0. Herd immunity does not work at a country level but at a community or cluster level.”

“So it is a completely wrong notion to say that if we reach X figure, everyone will be protected. No, we will as people move in and out of clusters too.”
Dr Shahid Jameel, virologist and Director, Trivedi School of Biosciences at Ashoka University

A recent study published in The Lancet found that the hard-hit city of Manaus, Brazil, had a resurgence of COVID-19, despite a high prevalence of people with antibodies. Experts found that one reason could be waning immunity from infections and the emergence of stronger variants.

Why are Cases Falling?

The ICMR serosurvey found that only 21 per cent of Indians over 18 had developed antibodies. “I can’t explain the downward trend in cases then, given the festive season, the unlock and then the ICMR results. Something is amiss somewhere.”

Dr Jameel added that we need more transparent data in the public domain on the survey such as which cities and areas were included to help understand the results.

“21.5 per cent will make sense as per the curve only if the main cities where seropositivity is high or around 50 per cent such as Delhi and Pune are not included. The only big cities were Chennai and Bangalore.”
Dr Shahid Jameel, virologist and Director, Trivedi School of Biosciences at Ashoka University

So it could be that since the survey was looking at smaller areas where the “infection would progress more slowly simply because the is population density is lesser.”

Continuing its streak of low numbers of single-day coronavirus cases, India reported 12,408 new infections in the last 24 hours, increasing the overall tally to 1,08,02,591.

For over a week, the country has recorded less than 15,000 single-day cases.

“There are fewer cases and deaths in hospitals as well, and this is a harder figure to hide,” adds Dr Jameel.

Intensivist Dr Sumit Ray adds,

“Just because our cases are low right now does not mean there will not be a surge again. But we need to analyse larger seropositivity data from smaller regions within cities and this data needs to be made public. There is a possibility that certain areas have reached good levels and will have fewer cases - but this does not mean there will not be another surge. You have to be careful.”

So far, Dr Jameel says, we still don’t know enough. Do we have a weaker variant like other countries have a stronger one? “Maybe, but we have only sequenced 5000 viral genomes out 10 million cases, and with that density, we won’t know if we have a weaker mutation or not. The government is trying to sequence more but it will take at least 2-3 more months for the data to come out.”

Another possibility is that the virus may follow a cyclic pattern with highs and lows. Another could be that “enough people may be infected and this reduces the virulence of the virus, but we need more specific data for this,” adds Dr Jameel.

“I do believe that we have to be careful and wary still, we already know there are variants developing - what if tomorrow a variant develops that escapes these vaccines? It hasn't happened yet, but it’s possible. So it’s not over yet.”

ADVERTISEMENTREMOVE AD

So, When Will the Pandemic Be Over?

“So, COVID-19 will become endemic but this will not happen tomorrow. Once this cycle goes down, we may see restricted, localised outbreaks across the world and only then will it become endemic. Maybe then the virus will die down and become endemic and cause only maybe seasonal flu-like illness. But this is not for a few more years.”
Dr Shahid Jameel, virologist and Director, Trivedi School of Biosciences at Ashoka University

Perhaps the initial scare is over but COVID is not, “so wear a mask, get your vaccines when you can and be careful.”

“A vaccine won’t hurt you, since they are given to healthy people in trials (unlike drugs), safety is the most crucial aspect. If your turn comes, take the vaccine. How much it will help, we don't know since the efficacy of these vaccines are in controlled trials, and it drops by a few points when the vaccine moves out in a population - so the number crunching is useless.”

Our bottleneck is not the shortage of vaccines but that we don’t have enough centres and people to administer the vaccine. “We have 3000 centres to give the vaccines across the country. Each of these can administer one shot to 100 people a day, which becomes 3 lakh a year. In a 30 crore priority group, this will take roughly 3 years.”

Dr Jameel also says he did not account for holidays and only accounted for one dose when you need two, so the reality of this timeline will be longer.

“We need to work on increasing our capacity,”says Dr Jameel.

Published: 
Speaking truth to power requires allies like you.
Become a Member
Monthly
6-Monthly
Annual
Check Member Benefits
×
×