Explained: When to roll out booster jabs

🔴 The WHO has said such a decision should be evidence-based. What is the evidence on protection given by a regular course and an additional jab? What is India considering; which vaccines are likely to be used?

Covid-19 vaccines, Covid vaccines, Covid booster shots, World Health Organization WHO, booster jabs, booster vaccines, Explained, Indian express, Indian express explained

It said the evidence till date “indicates” a “minimal to modest” reduction of vaccine protection against severe disease over six months after the second dose. (File/Partha Paul)

In an interim statement on Wednesday, the World Health Organization (WHO) said the introduction of booster doses of Covid-19 vaccines should be “firmly evidence-driven” and targeted to groups at highest risk of serious disease and frontline workers. It said the evidence till date “indicates” a “minimal to modest” reduction of vaccine protection against severe disease over six months after the second dose.

What is this evidence?

On December 7, the WHO’s Strategic Advisory Group of Experts on Immunisation conducted a systematic review of 18 studies on vaccine effectiveness, conducted in various countries (not including India) between June 17 and December 2. The vaccines assessed were those Pfizer, Moderna, AstraZeneca (used in India as Covishield), and Johnson & Johnson.

The review estimated the average change in vaccine effectiveness (VE) from 1-6 months after full vaccination. For symptomatic disease, VE decreased by 32% for older adults (above 50) and 25.4% for all ages. For severe disease, it decreased by 9.7% for older adults, and 8% for all ages. The review summarised that:

⦿ Moderate decrease in VE after 6 months for infection and any symptomatic disease

⦿ Minimal decrease of VE over time against severe disease

⦿ Continued follow-up of VE after 6 months is needed, and for more vaccines

⦿ The impact of Omicron on waning VE is not known

Are these rates good news or bad?

Leading public health expert Dr Srinath Reddy, president of the Public Health Foundation of India, said one should look at two specific data points: age-specific data, and breakthrough infections causing severe disease.

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“I would be interested in seeing the data for severe illness in 50-plus, 60-plus, and 70-plus. Let us say, for 60-plus it is 18 %, and 70-plus is 25%. Then we are in trouble,” he said.

“We have to see how many of the breakthrough infections are classified as a severe infection. Because if it is mild to moderate, it is not a cause for concern.” He added: “Because India also has comorbidities at a younger age, I would also like to look at data at 45-55 plus and the level of severity.”

How soon should India ideally start booster doses?

Referring to the WHO statement, V K Paul, head of the national Covid-19 task force, said: “… It [the decision in India] has to be driven by science that is applicable to our situation, driven by science that is applicable to our vaccines. What you read largely is about other platform vaccines in different settings, and with a different profile of comorbidities, and age profiles in some ways,” he said.

“There are intense efforts to culture the virus and we will test our vaccines [against Omicron]. Be rest assured the decision for adolescent vaccination and booster doses will be taken on scientific principles and overarching interest of people of India,” he said.

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States such as Maharashtra, Kerala and Delhi have repeatedly asked the Centre to begin booster doses. So have the Indian Medical Association (IMA) and many health experts.

“We are very upset about the delay. The UK and some other countries are taking up third dose vaccination. We are told that there is a need for evidence to clear the booster doses. We know for sure the warning signs are there and the government should act proactively,” IMA president Dr J A Jayalal said.

Dr Subhash Salunkhe, member of the Covid task force, said booster doses can begin even while primary doses are being given. “This is not an either/or situation. It has to be done concurrently. Those who need the second dose are definitely a priority but the third dose is also required, especially for immuno-compromised persons and healthcare workers.”

What aspects are experts considering ?

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The National Technical Advisory Group on Immunisation (NTAGI) is examining data from across the world as well as from India on three aspects: T-cell response, antibody response with a particular vaccine and with another vaccine, and how long immunity persists after infection, said Indian Council of Medical Research (ICMR) chief Dr Balram Bhargava.

Sources said the ICMR’s real-time tracker shows breakthrough infections are less than 2% in the general population, and around 7% among doctors and nurses.

Sources said there is a detailed discourse on an additional dose focusing on cellular immunity from memory cells, which play an important role in providing protection against severe disease and hospitalisation.

Also, the source said, “certain dates, and, timelines, are very important. A majority of India’s adult population received their first dose immediately prior to the second wave, and the second dose, most of the adult population definitely received it after the second wave… A substantial proportion has already received an ‘additional dose’ in terms of antibody response from the April-May Delta surge. How this impacts immunity is being scientifically examined,” the source said.

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Must Read | Explained: Omicron rising, but Delta still dominant

Which vaccines can potentially be used as boosters in India?

While NTAGI is examining scientific evidence, a preliminary consensus has been arrived at: if one has taken an inactivated-whole virus (eg Covaxin) or adenoviral vector vaccine (eg Covishield or AstraZeneca’s vaccine), the third dose should not be of the same platform.

Preliminary studies from outside India suggest that a third dose of the AstraZeneca vaccine is effective against the Omicron variant. The emerging data too will be examined.

If and when the recommendation is made, eligible recipients are likely to have multiple options in the coming months, such as:

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⦿ Hyderabad-based Biological-E’s Corbevax, a protein subunit vaccine that contains only the antigenic parts of the virus

⦿ Serum Institute of India’s (SII) Covovax, a recombinant nanoparticle protein-based vaccine, for which US-based Novavax and SII have already received emergency use authorisation in the Philippines

⦿ Bharat Biotech’s intranasal vaccine which, sources said, is expected to come in the second half of January.

⦿ India’s first m-RNA Covid-19 vaccine developed by Pune-based Gennova Biopharmaceuticals Ltd which, the government has said, is expected to produce 6 crore doses.

Kaunain Sheriff M

As City Editor ( Delhi) at the Indian Express, Kaunain Sheriff leads city reporting with a sharp focus on accountability journalism, data-driven stories, and ground-level impact. As the National Health Editor he leads the newsroom’s in-depth coverage of pressing health issues. He is the author of Johnson & Johnson Files: The Indian Secrets of a Global Giant, a definitive investigation into the accountability of one of the world’s most powerful pharmaceutical corporations. Areas of Expertise Investigative Reporting: Has deep expertise in investigative reporting spanning public health, regulatory affairs, drug safety, and the criminal justice system. His work sits at the intersection of governance, law, and accountability, with a particular focus on how regulatory failures, institutional lapses, and policy decisions affect citizens’ rights and safety. Data Journalism: Has extensively on big data–driven investigations, including analyses of flagship government schemes and large datasets on criminal trials, uncovering systemic gaps. Global Collaborations Kaunain is a key contributor to major international journalistic projects: The Implant Files: Collaborated with the International Consortium of Investigative Journalists (ICIJ) to expose global malpractices in the medical device industry. Chinese Big-Data Investigation: Uncovered how a foreign data firm monitored thousands of prominent Indian institutions and individuals in real-time. Awards & Recognition His commitment to "Journalism of Courage" has been recognized with the industry's highest honors: Ramnath Goenka Award for Excellence in Journalism SOPA Award (Society of Publishers in Asia) Red Ink Award (Mumbai Press Club) Indian Express Excellence Awards (Triple recipient for investigations into the NSA abuse in UP, Vyapam scam, and the anti-Sikh riots). Education: Studied Mechanical Engineering at Visvesvaraya Technological University (VTU), Bangalore, before moving to Delhi to pursue his passion for journalism. His engineering training informs his analytical approach, enabling him to decode technical, legal, and data-heavy systems with precision. Social media LinkedIn: linkedin.com/in/kaunain-sheriff-3a00ab99 X ( fromerly Twitter): @kaunain_s ... Read More

Anuradha Mascarenhas

Anuradha Mascarenhas is a Senior Editor at The Indian Express, based in Pune. With a career spanning three decades, she is one of the most respected voices in Indian journalism regarding healthcare, science and environment and research developments. She also takes a keen interest in covering women's issues . Professional Background Education: A gold medalist in Communication and Journalism from Savitribai Phule Pune University and a Master’s degree in Literature. Author: She authored the biography At The Wheel Of Research, which chronicles the life and work of Dr. Soumya Swaminathan, the former Chief Scientist at the WHO. Key Focus: She combines scientific accuracy with storytelling, translating complex medical research into compelling public and human-interest narratives. Awards and Recognition Anuradha has won several awards including the Press Council of India's national award for excellence in journalism under the gender based reporting category in 2019 and the Laadli Media award (gender sensitivity -2024). A recipient of the Lokmat journalism award (gender category-2022), she was also shortlisted for the RedInk awards for excellence in journalism-2021. Her debut book At The Wheel Of Research, an exclusive biography of Dr Soumya Swaminathan the inaugural chief scientist of World Health Organisation was also nominated in the Popular Choice Category of JK Paper AUTHER awards. She has also secured competitive fellowships including the Laadli Media Fellowship (2022), the Survivors Against TB – New Research in TB Media Fellowship (2023) and is part of the prestigious 2025 India Cohort of the WomenLift Health Leadership Journey.” Recent Notable Articles (Late 2025) 1. Cancer & Specialized Medical Care "Tata Memorial finds way to kill drug-resistant cancer cells" (Nov 26, 2025): Reporting on a breakthrough for triple-negative breast cancer, one of the most aggressive forms of the disease. Discipline, diet and purpose; How a 97-year-old professor defies ageing'' (Nov 15, 2025) Report about Prof Gururaj Mutalik, the first Head of Department at Pune's B J Government Medical College who at 97 credits his longevity to healthy habits and a strong sense of purpose. 2. Environmental Health (The "Breathless Pune" Series) Long-term exposure even to 'moderate' air leads to chronic heart, lung, kidney issues" (Nov 26, 2025): Part of an investigative series highlighting that even "safe" pollution levels are damaging to vital organs. "For every 10 µg/m3 increase in PM2.5 level, there was 6-8% jump in medicine sales" (Nov 23, 2025): Using commercial data to prove the direct link between air quality and respiratory illnesses in Pune. 3. Lifestyle & Wellness News "They didn't let cancer, diabetes and heart disease stop them from travelling" (Dec 22, 2025): A collaborative piece featuring survivors who share practical tips for traveling with chronic conditions. At 17, his BP shot up to 200/120 mmHG; Lancet study flags why child and teen hypertension doubled between 2000 and 2020'' (Nov 12,2025)--A report that focusses on 17-year-old-boy's hypertensive crisis and reflects the rising global trend of high blood pressure among children and adolescents. 4. Scientific Recognition & Infrastructure For promoting sci-comm, gender diversity: IUCAA woman prof highlighted in Nature" (Nov 25, 2025): Covering the global recognition of Indian women scientists in gender studies and physics. Pune researchers find a spiral galaxy like the Milky Way from early universe'' (December 3, 2025)- A report on how Indian researchers discovered a massive galaxy that existed when the universe was just 1.5 billion years old , one of the earliest to have been observed so far. Signature Beat: Health, Science & Women in Leadership Anuradha is known for her COVID-19 reportage, where she was one of the first journalists to provide detailed insights into the Covishield and Covaxin trials. She has a dedicated interest in gender diversity in health and science, often profiling women researchers who are breaking the "leaky pipeline" in STEM fields. Her writing style is scrupulous, often featuring interviews with top-tier scientists and health experts from various institutions. ... Read More