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Basis for precaution dose approval not clear

There has been just one study each for Covishield and Covaxin to understand vaccine effectiveness despite being granted EUA 12 months ago

January 01, 2022 08:10 pm | Updated January 05, 2022 07:07 am IST

On November 22 last year, Dr. Balram Bhargava, Director-General of ICMR, said there is “no scientific evidence so far to support the need for a booster vaccine dose against COVID-19.” He said the primary focus of the government was on giving a second dose of the vaccine to make people fully vaccinated. “Administering the second dose of COVID-19 vaccine to all adult population and ensuring that not only India but the entire world gets vaccinated is the priority of the government for now,” he said. A day earlier, Dr. Samiran Panda, Head of ICMR’s Epidemiology and Communicable Diseases Division said scientific evidence does not support booster doses. “Right now, the scientific evidence from within the country does not underline the need for a booster dose. Public health considerations are on the priority now,” he told the news agency Asian News International.

In mid-December 2021, Dr. Jayaprakash Muliyil, member of NTAGI told The Outlook: “There is no need for a booster dose as the memory cells will produce the specific antibody once the virus comes in contact with a vaccinated or a naturally recovered person.”

Precaution dose

Yet, a “precaution dose” was approved by the government on December 25, 2021. Prime Minister Narendra Modi announced the decision to begin administering the precaution dose from January 10 onwards for health-care and frontline workers and people older than 60 years with comorbidities. No new studies have come in the public domain to support an additional dose since Dr. Bhargava said on November 22 that no scientific evidence was available to support a booster shot.

Early data from South Africa and the U.K. indicate that the Omicron variant does not cause severe disease or death in fully vaccinated people. But there is a time lag between infection and hospitalisation. The protection offered by vaccines available here against the variant in older people and other vulnerable populations is not known.

Omicron threat?

Whether the decision to approve the precaution dose was based on the emergence of the Omicron variant but in the absence of vaccine effectiveness data is not clear. There was no explanation on why the government revised its earlier stand and decided to provide an additional dose before increasing second dose coverage either. “In fact, the Omicron variant makes a strong case to increase primary vaccination coverage considering the preliminary data from South Africa and the U.K.,” says immunologist Dr. Satyajit Rath formerly with the National Institute of Immunology, Delhi. Across age groups, nearly 90% have received the first dose but only 64% are fully vaccinated, and 21.5% of those older than 60 years are yet to be fully vaccinated, as on December 31, 2021.

There has been just one study each for Covishield and Covaxin to understand vaccine effectiveness (before Omicron emerged) despite the vaccines being granted an emergency use approval 12 months ago and after administering 1.45 billion vaccine doses. The study on Covaxin did not even look at the effectiveness of the vaccine in preventing severe disease and death.

Incidentally, immunocompromised people have not been included like in most of the 126 countries that have approved a booster shot. “A third dose or additional dose for immunocompromised is something on which experts have consensus. [Unlike many countries] in India, where third shot is recommended for sub-group of population only, a separate policy on third shot for immunocompromised is urgently needed,” says Dr. Chandrakant Lahariya, physician-epidemiologist and public policy and health systems specialist.

“But a key question is if an immunocompromised individual has not developed sufficient antibodies after two shots, will a third dose result in increased antibodies? We know that third shot results in increased antibodies in immunocompromised individuals after an mRNA vaccine. However, [as to] whether it is true for other vaccines or not, we don’t have evidence. For this population sub-group, making a choice on the right vaccines is very important,” Dr. Lahariya says.

In a press conference on December 30 last year, Dr. Bhargava, while not providing any scientific reason or evidence for deciding on approving a booster shot to the three categories, did point out to studies that had found evidence of protection offered by natural infection lasting up to nine months. This was to tell why the government has decided to provide the precaution dose nine months after the second dose.

Hybrid immunity

The emphasis was on hybrid immunity (immunity produced by natural infection followed by vaccination) being superior to immunity conferred by infection and full vaccination in infection-naïve people, which was known many months ago, to support the decision to administer the precaution dose nine months after the second dose. Dr. Bhargava cited the 67% seroprevalence in the last sero survey to drive home the point that many people who have been vaccinated would be possessing hybrid immunity. The sero surveys are not truly representative of infection spread in the community, says Dr. Rath. If hybrid immunity in India is high, why provide an additional dose at all, he asks.

“We know that the longer the gap, the better the boosting effect. Since India has made the decision to administer precaution shots, this is the longest gap which could have been considered, especially if the precaution dose has to be administered from January 10 onwards,” says Dr. Lahariya.

Limited use

One of the studies cited by Dr. Bhargava and carried out by researchers from CSIR’s Indian Institute of Chemical Biology, Kolkata looked at cellular immunity among vaccinated and naturally infected people. The researchers found that T cell immunity from natural infection lasted as long as 10 months. But they did not measure the duration of protection offered by T cell immunity in fully vaccinated people who have not been previously infected. There is now overwhelming evidence that natural infection provides better protection than vaccination with two doses. “They [T cell immunity studies] are not robustly quantitative. All they can say is yes, there is some T cell response, which is not surprising and is of limited use,” says Dr. Rath.

Choice of vaccine

All the other Indian studies cited by Dr. Bhargava which looked at the duration of protection had measured only the humoral immunity and neutralising antibodies. But with breakthrough infections being far more common with the Omicron variant than the Delta variant, these studies have little relevance in making policy decisions. Also, the primary objective of COVID-19 vaccination is to prevent severe disease and death and not infection prevention.

For instance, a study undertaken by researchers from ICMR’s National Institute of Epidemiology, Chennai, which Dr. Bhargava mentioned, found the humoral immune response persisting up to seven months in naturally infected people. But the study was carried out in late 2020 before the emergence of the Delta variant and the massive second wave caused by it swept through the country.

The Union Health Minister Mansukh Mandaviya made an assurance on December 3 last year that the government will go by scientific advice to decide on booster doses. But on December 25, when the government approved the additional dose and even now there is no clarity on whether the booster dose will be with the same vaccine that an individual has got for the first two doses or a different one.

“Scientific evidence is that the preferred booster will be a vaccine developed using a different platform,” says Dr. Lahariya. “The Indian government is exploring the feasibility of recently licensed protein-based COVID-19 vaccines available for booster dose. I am of the opinion that in the case of Covishield, the booster should be protein-based vaccines — Covovax (data of its boosting effect is already available) and then Corbevax. The homologous booster would be the best approach for Covaxin, till we have evidence on heterologous boosting for Covaxin.”

But Covovax and Corbevax were granted emergency use approval only on December 28, three days after the government announced a booster dose for select groups. “If the government was waiting for scientific evidence on booster doses, why did it hurry before deciding on whether the booster should be a homologous [same] or heterologous [different] one,” asks a senior scientist who did not want to be named.

No trials for booster

Incidentally, there is no scientific evidence from clinical trials in India on the efficacy of Covishield or Covaxin as booster shots. Permission to conduct the first clinical study in India to understand the performance of a vaccine as a booster was granted only on December 29; Bio E was given permission to conduct the trial using Corbevax as a booster dose. While the Subject Expert Committee denied permission on December 10 to Serum Institute to administer Covishield as booster doses till it submits clinical trial data, Covaxin will be used as a booster dose despite no clinical trial for efficacy being conducted. According to News18, Bharat Biotech had sought permission to conduct a clinical trial to test the efficacy of Covaxin as a booster dose only after the Prime Minister’s announcement on December 25.

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