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Explained: When to roll out booster jabs

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.

“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.

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 ?

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.

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:

⦿ 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.




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