Coronavirus | Opeds and editorials

A serosurvey template for the whole of India

The Ahmedabad Municipal Corporation (AMC) needs to be complimented for conducting seroprevalence studies on its own. The latest seroprevalence done in June 2021, for which the data was released a few days ago, has shown that the city population has COVID-19 antibodies in 81% of the population sampled. This is one of the highest rates seen anywhere. The study only measured antibodies, as there are no easy methods to check cell-mediated immunity or neutralising antibodies. Some studies in other countries have shown that besides the antibodies, there is a substantial proportion of infected people who will not show antibodies but will have cell-mediated immunity.

Studies in Ahmedabad in earlier rounds of sero-surveillance showed that up to 30% of the population with past infection, which is not recent, do not show antibodies in such surveys. It is possible that the waning of antibodies and cell-mediated immunity together can indicate that an additional 10-15% of persons might be protected. Therefore, the proportion of people with some immunity protection at the population level in Ahmedabad may be close to 90-95%.


On herd immunity

The Ahmedabad Municipal Corporation is one of the most progressive municipal corporations to use serosurveys evidence to plan and decide the course of action. As part of the COVID-19 control work, besides the routine testing, tracing and isolation work — that most cities or districts have done — the Ahmedabad Municipal Corporation also invested in conducting periodic sero-surveillance of its own. It is time to use the efforts of Ahmedabad city as a case study to revisit the discussion on the threshold for herd immunity.

At the national level, the National Institute of Epidemiology (NIE) of the Indian Council of Medical Research (ICMR) has conducted four rounds of serosurvey; the Council of Scientific & Industrial Research (CSIR) too conducted a nationwide serosurvey. The States, including Karnataka, Kerala, Haryana, West Bengal, Odisha, Maharashtra, Gujarat, Delhi, Tamil Nadu and Punjab, have done citywide population-based serosurveys. The sero-surveillance from cities show the percent of the population infected with the virus and has antibodies in a specific time period. The threshold for herd or population-level immunity is a local geographical phenomenon, wherein the population or herd is intermixing with each other and spreading the disease within itself. Hence, it is reliable only to estimate the level of immunity at the city or town level, given that there are no sizeable amounts of migration occurring, changing the population dynamics of transmission.

For example, in Gujarat, two nearby cities,Ahmedabad and Baroda, behave as two separate communities or herds as there is not much travel and intermixing between the people of the two cities compared to mixing within the same city. So, both cities may have very different immunity levels — say 80% in one and 20% in another. So, the disease might infect many people, as a greater proportion of the susceptible are present in the city with 20% immunity but not spread greatly in the city with higher levels of protection, say 80% immunity.


Some serosurveys which combine smaller numbers from multiple studies might be misleading. For example, suppose we do a common study between two cities. In that case, we may estimate 55% of persons having immunity — inferring that both cities have a high degree of vulnerability. While a limited inference will mean that the disease will spread equally in both cities, it is not completely true as one city will have a lower burden in the future, with 80% of people having some form of immune response. Each of the major cities or towns must conduct its own sero-surveillance to estimate the level of protection and estimate the proportion of the susceptible population in that city.

Other surveys

A nationally representative sample of serosurveys is useful to provide a bird’s-eye view of the situation. The NIE should be complimented for its efforts and for conducting four rounds of serosurveys over the last 15 months. The efforts led by the Ministry of Health and Family Welfare, Government of India and the World Health Organization’s tuberculosis programme in the field and technical partnership led by the NIE are praiseworthy for any public health agency; comparable to the best in class in a rigorous process, and peer-reviewed publications in high impact journals.

Opinion | Serosurveys underestimate building of herd immunity

The results from these surveys showed that antibody levels increased from 0.7% in April 2020 to 67% in June 2021. There is also not much of a difference between urban-rural, and male-female groups. A higher prevalence is seen in people above the age of 45, in vaccinated people and health-care workers. But one must understand that all these are average numbers from a study of a total sample of about 29,000 people. As the sample is taken scientifically, we have to assume that it represents the true situation in the country. While the aggregated data at the national level inspires the good work done by the NIE-ICMR scientists and other researchers in the collaboration, it is not a reason to celebrate in enthusing unreasonable optimism. We should be careful and not jump the gun in declaring that we are nearing the threshold of population immunity at the national level.

We can still have major outbreaks in specific geographical regions in the future, as seen in the United Kingdom, Israel, and others. There will also be regional and State-wise differences. Urban areas, as sampled by the ICMR study, showed a prevalence of 69% — slightly higher than in the rural areas, which had a figure of 65%. The rural areas have a greater spread of the virus similar to urban areas, despite rural areas being less congested with lower social interactions. There is not much crowding in the rural areas as seen in urban areas. Compared to the Indian urban sample of the ICMR, the Ahmedabad city seropositivity is higher at 81%. The time ahead will be a marker to know how many cases will be detected in Ahmedabad and how transmission dynamics and seroprevalence will change in the future. Hence, the surveys in this city provide a good case study for the country to review and plan city-specific actions.

Ahmedabad experienced a very bad second wave. A similar second wave was also seen in Delhi, Mumbai, Bengaluru and other big cities. If sero-surveillance is done in these cities, we may see very high levels of antibodies. Urban local bodies and State governments should launch rapid and successive rounds of serosurveys.


Aiding policy making

A more efficient way is to set up sentinel surveillance sites in all public hospitals and estimate the trend in overall seroprevalence. One such effort was done by Karnataka in utilising the strengths of the National Aids Control Organization’s field team along with technical supervision by multiple academic institutions in Bengaluru, including the Public Health Foundation of India, the Indian Institute of Science, the Indian Statistical Institute, etc. These efforts can guide and inform decisions on the extent to which the city’s business, educational institutions, and markets can be opened up. Wider and faster vaccination coverage is an additional and absolute necessity.

The distribution of vaccines, stepping up the hospital response, and severity in future waves can be understood and addressed by the periodic antibody prevalence from serosurveys. Based on sero-surveillance studies, such an evidence-based approach will be very useful in the process of decision making while unlocking cities and increasing economic activities. Till supply constraints are completely resolved, it will also help deploy scarce vaccine resources to the places in most need of them. Also, sero-surveillance does not cost much — at a price of ₹500 per test, it will cost ₹25 lakh to test 5,000 people. This is not a major cost for any major city. We constantly face one problem: cities do not have mechanisms to use evidence generation and analysis expertise from public health professionals including epidemiologists.

Watch | What are serological surveys?

In summary, every major city with a population of more than 10 lakh should do a rapid sero-surveillance survey and set up sentinel surveillance to confirm the protection levels in the existing population and plan. It is time to use the information on existing levels of antibodies in the population to guide evidence-based policymaking. These efforts will help understand and mitigate the risk of opening up the economy and society, and deciding the priority for vaccination. Over 40 cities have a million population, and another 300 cities have a population between one lakh to 10 lakh. There is an urgent need to take up sero-surveillance studies to help guide the COVID-19 control strategy throughout rural and urban India.

Dr. Dileep Mavalankar is Director, Indian Institute of Public Health, Gandhinagar. Dr. Giridhara R. Babu is a Professor, Head-Lifecourse Epidemiology at the Public Health Foundation of India

Our code of editorial values

Related Topics
This article is closed for comments.
Please Email the Editor

Printable version | Sep 18, 2021 3:57:13 PM |

In This Package
Cracking the whip: On Joe Biden’s vaccine mandates
Should children be given COVID-19 jabs?
The lag between jabs: On Covishield gap
Back at school: On student safety
Breakthrough challenge: On vaccines and the virus variants
The prognosis for school reopenings
Effectiveness of vaccines
Kerala’s rising COVID-19 cases explained
Learning safely: On schools reopening
A surfeit of sero surveys
Curbing Delta: On the variant that drives India’s COVID-19 infections
Focusing on diseases sidelined by COVID-19
Lessons from India’s all-cause mortality data
Safe at school: On getting students back on campus
The importance of the booster dose to plan ahead
A call for improving civil registration systems
Pandemic of distrust: On resisting COVID-19 vaccination
Vaccinating the young: On priority groups
You are reading
A serosurvey template for the whole of India
Making decisions under stress
Dealing with denial: On playing down the COVID-19 tragedy
A cardinal omission in the COVID-19 package
Rising again: On global rise of fresh COVID-19 cases
Ramping up supply: On COVID-19 vaccination woes
Upholding trust in vaccination
Caution and optimism: On preventing the third wave
Countering the next wave of COVID-19
Stopping the surge: On unlock and the next COVID-19 wave
A welcome spike: On India’s COVID-19 vaccination record
A time to give: On ex-gratia compensation to families of COVID-19 victims
Focus on COVID-19 estimated deaths
What needs to be done with vaccines
Counting the dead: On measuring excess deaths
Refocused vaccination campaigns are possible
Bring genomic sequencing into the pandemic fight
Preparing for the next COVID-19 wave
Connecting the dots to mitigate a third wave
The red flags on the trail of the virus
Behaviorial change can reduce transmission
Adverse changes, federalism imperilled
Close the vaccination gap, in global lockstep
Only a global effort can tame COVID-19
Addressing vaccine hesitancy
Naturally, selection: On vaccinating the vulnerable in 18+ group
Vaccination is our only weapon
Extending safety: On deferring second dose of COVID-19 vaccine
The AIDS fight offers a COVID vaccine patent pathway
The basics of an effective vaccine policy
Using all options: On Covaxin licensing
State action: On Centre’s role in COVID-19 fight
COVID mishandling foretold in the Budget
A matter of concern: On Indian coronavirus variant
Vaccine skirmishes: On production of COVID-19 vaccine
Lockdown gains: On need to augment health system
Social murder and the missing state
A CT scan for COVID merits a word of caution
To stop a third wave, India has to mask up
Is the government committed to vaccine equity?
Salutary steps: On Election Commission norms to curb COVID-19 spread
Shortage and wastage: On cutting vaccine wastage
Gasping for air, gasping for answers
Misinformed and misleading
Right priorities: On U.S. COVID-19 aid to India
A patently wrong regime
Tips for managing COVID-19 at home: the dos & don’ts
Undermining ‘vaccination for all’
Another wave spells more nutrition loss
Unfair and dangerous: On vaccine inequity
Viral load: On lockdowns, lives and livelihoods
The road ahead in India’s augmented vaccination drive
Infernal infernos: On hospital fires amid the pandemic
Too little: On the Election Commission’s COVID-19 curbs
India’s COVID crisis — when difficult became worse
A descent into disillusionment and chaos
Open and safe: On Modi government’s vaccination policy
A recipe for vaccine inequity
Vaccine diplomacy that needs specific clarifications
On the trail of the second wave’s dynamics
How can India contain the second wave?
Lessons from the first wave
Examination priorities: On annual exams amid the pandemic
The secrecy around deaths after vaccination
Indian universities need immediate vaccination
Lessons from COVID-19
The second wave: On why new COVID-19 vaccines should be cleared
Weighing in on the saga of a vaccine
Rising poverty: On pandemic-induced disparities
A booster shot for India’s vaccination plan
Allaying concerns: On public trust and vaccination programmes
A moral test: On the vaccine divide
Efficacious too: On Covaxin
Sustaining the drive: On COVID-19 vaccination phase 2
Vaccine inequities: On need to vaccinate all above 45
Addressing vaccine reluctance and policy hesitancy
Redefining the exit plan for COVID-19
Boosting confidence: On need for efficient use of COVID-19 vaccine stocks
Opening up the vaccine market
Origin and spread: On the source of SARS-CoV-2
New questions: On COVID-19 infecting one-fifth of Indian population
A year on, mind the gaps in the pandemic response
Should Board exams be conducted in one go this year?
No to vaccine nationalism, yes to global cooperation
Tempered optimism: On India’s sliding COVID-19 graph
The best shot against COVID-19
More vaccines than takers
Managing the rollout: On addressing vaccine hesitancy
Injecting confidence: On India’s COVID-19 vaccination drive
Vaccine optimism and the scientific uncertainty link
Building trust in vaccines
The debilitating side-effect of a flawed vaccine trial
Gearing up: On vaccines and public trust
A hurried gamble: On vaccines and transparency
The second dose: On COVID-19 vaccine
A constant vigil: On the new coronavirus strain in India
Unmasked, reflections on the pandemic and life
Caution pays: On Centre’s COVID-19 surveillance guidelines
Towards an effective vaccination distribution policy
Essential dry run: On COVID-19 vaccination drive
COVID-19 and limits of political accountability
The purpose of a vaccine
Clear the fog, draw up a clear vaccination policy
Rein in the vaccine nationalism, the profiteering
In vaccine race last lap, the key steps for India
The storage tale of two vaccines
T-cell immunity and COVID-19
COVID-19, climate and carbon neutrality
Signs of easing: On India’s COVID-19 fight
Has India passed the COVID-19 peak?
Sooner, better: On indigenously developed COVID-19 test kits
The battered Puja economy
Outline of a pandemic fight, by and for citizens
Pandemics and the collective consciousness
Vaccines with a global common good guarantee
Saving lives under the long shadow of the pandemic
Until vaccine: On Unlock 5
The challenge of changing health behaviour
Weighing the costs: On COVID-19 vaccine
The slow and frustrating journey of recovering from COVID-19
Health worker safety deserves a second look
Unlocking campuses: On UGC’s revised academic calendar
Recovery from COVID-19 can be a struggle
Uniting to combat COVID-19
Coronavirus fears and preconception advice
An agriculture-led revival as flawed claim
A necessary pause: On the COVID-19 vaccine race
The uncertainties over COVID-19 numbers
The challenges in counting the dead
COVID-19 deaths may be higher than reported
The many challenges in estimating deaths
Alone at the top: On India’s COVID-19 numbers
The participants we need in Phase 3 trials
Differential impact of COVID-19 and the lockdown
More than a vaccine, it is about vaccination
COVID-19 and a country club India must leave
A quest for order amid cyber insecurity
Adopting a public systems approach to COVID-19
Milestone of a million: On India’s COVID-19 numbers
Testing times: On university exams
Predictions, pandemics and public health
It’s time to flatten the pandemic stereotyping
Viral outrage only spikes the data
Sending the right message
Needed: Clear testing data
The social contract needs to be rewritten
The pandemic is about eyes shut
Joblessness and opportunity in Tamil Nadu
Green-lighting ecological decimation amidst a pandemic
COVID-19 has no religion
A case for extension: On rural jobs scheme
Surely, even if slowly: On a COVID-19 vaccine
Bend it like Italy: On flattening the COVID-19 curve
Promise and delivery: On India’s first COVID-19 vaccine
States hold the key: On Unlock 2.0
PCR testing is a double-edged sword
Science vs nonsense: On Patanjali’s COVID-19 claim
Shut and open: On tennis during the pandemic
The perils of follow the leader syndrome
The many questions about Favipiravir
In new lockdown, a second chance for Tamil Nadu
United front in Delhi: On Kejriwal government-Centre camaraderie
A prescription of equitable and effective care
Multilateralism post COVID-19
Making public transport safe during COVID-19
A better rate: On COVID-19 recovery
Look back in relief: On the migrant labour crisis
Needed, a transfusion for public health care
Wrong priorities: On keeping religious places open during a pandemic
Crossing the line: On Delhi’s decision to limit health services
Profit, not profiteering: On regulation of COVID-19 testing charges
In Persian Gulf littoral, cooperative security is key
Paging the private sector in the COVID fight
Curves and recoveries: On India’s coronavirus numbers
India’s Parliament is missing in action
Axing the economy’s trunk
Scripting a new narrative for COVID control
Open with caution: On Unlock 1
It’s time for a universal basic income programme in India
The waning of subaltern solidarity for Hindutva
Export blocks: On India’s trade amid the pandemic
A moment to trust the teacher
The echo of migrant footfalls and the silence on policy
Enjoying the fruits of their labour
Helping supply chains recover
The heavy burden of social suffering
An effective lockdown
The lockdown has highlighted stark inequalities
Will sport be the same in empty stadia?
Cinema after COVID-19
The eternal longing for the distant home
Working safely: On workplaces during the pandemic
A hole in the whole: On health sector woes
China, better prepared for the post-COVID world
How public health boosts an economy
Keep it retrospective
Backing the ‘angels in white coats’
Standstill: On opening of stadia for training
Flawed stimulus is justice denied
We need social physicians
A callous response
Peaking: On India’s coronavirus tally
Farm gate in focus: On amending Essential Commodities Act
A question of quarantine: On migrant workers and other travellers
TASMAC tribulations: On Tamil Nadu liquor sale
The pandemic and the challenge of behaviour change
One for the poor: On Centre’s corona package
Lockdown syndrome: On virus-induced economic crisis
Are India’s labour laws too restrictive?
Stop the return to laissez-faire
States cannot be left to the Centre’s mercy
Local motif: On Modi’s call for self-reliance
Liquidity lifeline: On Nirmala’s MSME package
A plan to revive a broken economy
Provide income support, restore jobs
Perilous state: On State finances
COVID-19 and the path ahead
Reaffirm cooperative federalism
Riding roughshod over State governments
Tragedy on the tracks: On the killing of 16 migrant workers
Coming to terms: On India refusing to admit community transmission
The trends shaping the post-COVID-19 world
The epidemic and ensuring safety in courts
Responding to COVID-19 at the grassroots
The face of exploitation
Contempt for labour: On dilution of labour laws
Slower growth and a tighter fiscal
Back home: On return of Indian expatriates
Blame game: On Donald Trump’s anti-China rhetoric over COVID-19
Resuscitating multilateralism with India’s help
A war-like state and a bond to the rescue
Fear and loathing in the land of the free
Everyone wants a good stimulus
Rent control amidst pandemic
Slow release: On lockdown 3.0
No comfort in numbers: On Bengal’s coronavirus cases
Pandemics without borders, South Asia’s evolution
India’s disease surveillance system needs a reboot
No relief for the nowhere people
BRICS against COVID-19
Recovering early: On India’s COVID-19 patients
It’s about food, nutrition and livelihood security
Taiwan’s coronavirus protocol shows how it is done
Needed: a pandemic patent pool
Getty Images/iStockphoto
Plasma therapy is no silver bullet
Take care of yourself too, fellow journalists
Strategic shift: On home isolation of mild coronavirus cases
Coping with today, planning for tomorrow
No end in sight: On India’s coronavirus strategy
Vividly imagining the life of migrant workers
A task for South Asia
Privacy concerns during a pandemic
Unlocking justice in the lockdown
Safe return: On migrant worker distress
The outline of another pandemic combat strategy
Pandemic and panic: On Tamil Nadu’s five-city lockdown
Protecting the poor from becoming poorer
Did SARS-CoV-2 begin from a lab?
Protection for protectors: On safety of healthcare workers
Rapid failures: On antibody testing kits
The COVID-19 paradox in South Asia
Fishing in troubled waters during a pandemic
How will India emerge out of the lockdown?
Making doctors wash hands
Locked out of cities, homes and livelihoods
Script of unity: On coronavirus and social prejudices
Exploiting a pandemic: On Trump’s immigration policy
The village is still relevant
A time for planetary solidarity
There may be no going back
No transparency in West Bengal
Focus on the curve: On India’s COVID-19 numbers
Economy in lockdown: On India’s worst case scenario
A shot of hope with a game changing vaccine
Caught in the heightened arc of communal polemics
Singing the corona tune
Helping a lending hand: On RBI’s second lockdown stimulus
A season of change: On IMD forecast system
A virus, social democracy, and dividends for Kerala
Across the gulf: On stranded Indian workers
Virtual reality: On telemedicine
A blueprint to revive the economy
A case to use JEE-Main instead of JEE-Advanced this year
Will the aviation industry recover from the pandemic?
Data-driven reporting during COVID-19
Stress test: On revised lockdown guidelines
Disastrous decision: On Trump halting funds to WHO
Cease the distractions, seize the moment
Getting the containment strategy in India right
In India’s response, a communications failure
Harmonising with nature
End the harassment of farmers now
A narrowing window: On extension of lockdown
Corona bond: On Eurozone COVID-19 rescue package
Halting the march of rumours
Polls during a pandemic
The pandemic and the contours of a health response
Economic liberalisation and its faults
Invasive, alien, most fearsome
Trade in tatters: On the global slump
Wanted, a collective national endeavour
Disingenuous and no antidote
COVID-19 and the crumbling world order
Women’s safety during lockdown
Lives and livelihoods: On economy after lockdown
Stage fright: On denying community transmission
Team India and winning the pandemic battle
In time of need: On hydroxychloroquine export
Will COVID-19 affect the course of globalisation?
Finding a scapegoat in WHO
Curating news for children during pandemic
A time for extraordinary action
For better use: On MPLADS funds
Needed, greater decentralisation of power
A key arsenal in rural India’s pandemic fight
Preparing for exit: On lifting the lockdown
Sanctions and pandemic: On America’s Iran policy
‘A script of action, responsibility and compassion’: Chief Minister Ashok Gehlot writes on Rajasthan’s fight against COVID-19
Taking a long view of the pandemic fight
Ten questions posed by the virus
A different economic approach
Why healthcare workers above 60 should be ‘benched’
Enemy at the gates: On Kerala-Karnataka border row
Reducing farm distress during a pandemic
Why everyone should wear masks
The criticality of community engagement
A niggardliness that is economically unwarranted
The spectre of a post-COVID-19 world
Light and sound: On Narendra Modi’s 9-minute light ceremony
A million and counting: On global coronavirus spread
Safe forests, safe people: On diseases of animal origin
Quarantine and the law
Making the private sector care for public health
Looking east to contain COVID-19
Limits to rugged individualism
Uncritical endorsement: On exodus of migrant workers and the Supreme Court
Beyond the blame game: On the Tablighi Jamaat episode
A long road: On India’s 21-day coronavirus lockdown
The missing notes: On politics and the fight against COVID-19
China’s zero: On China’s lead in containing coronavirus
Unprecedented step: On Wuhan lockdown
The return of the expert
Lessons from Hubei
A pandemic in an unequal India
Faith can’t override public health
Devising a people-centric response to COVID-19
Karnataka CM writes on how the State is fighting the pandemic
Tamil Nadu CM writes on how the State is stopping the pandemic in its tracks
The hunt for a cure begins with telling the truth
COVID-19 and a city’s anatomy
Long live the nation-state
The COVID cycle
Coronavirus | The worst of times, the best of times
It’s also a fight against punitive measures
The age of the neoliberal virus
The deep void in global leadership
Thinking national, acting local
Every man is a part of the main
Beyond social distancing to fight COVID-19
Next Story