It has been more than a week since India reported its first two cases of Omicron infection on December 2 in Karnataka. The genetic sequencing of samples of two travellers, aged 66 and 46, were found to be infected with this new variant which was originated from Botswana in Africa on November 9.
Since then over 40 cases of Omicron infections have been reported from various states like Maharashtra, Delhi, Chandigarh, Andhra Pradesh, Kerala etc. The variant hasn’t shown a high rate of transmission in India as of now as there is no report of any large outbreak from infected people in their respective areas.
Even the Ministry of Health and Family Welfare has predicted a low impact due to the presence of natural antibodies in a large number of people.
Despite that, a section of health experts has raised their concern in favour of booster doses of vaccine as they believe that it can increase the level of immunity in the body and will help protect from the new variant.
The US Food and Drug Administration (FDA) had introduced a booster dose in August for people above 18 years of age. Later on, on December 12, adolescents, aged 16 and 17, have also been made eligible for this additional dose.
Global shreds of evidence, incidentally, suggest that fully-vaccinated people or even those with booster doses are being infected with Omicron as well.
Besides, experts believe, there are several concerns that need to be addressed before any such booster shot is approved in India where people’s immune profile is quite unique.
At present, two vaccines, Covishield and Covaxin, are being administered to people above 18 years of age under the adult vaccination programme for Covid-19. The gap between two doses of Covishield and Covaxin is 12 and 4 weeks respectively.
Here’re the five most prominent concerns of a section of scientists and public health experts before the government in India takes a decision for the third dose.
No clinical trial of booster dose
Countries like the USA have introduced the booster dose, however, there is no clinical trial to assess its safety and efficacy anywhere in the world.
"I believe that we should first gather the clinical data of the third dose so that we can make out how safe and effective it is. Without proper study, I will not advise the government to authorise any additional dose,” Dr Syamal Roy, a noted immunologist, said. Dr Roy retired as Head of the Department of Infectious Diseases and Immunology, Indian Institute of Chemical Biology, Kolkata.
Some immunologists believe that higher antibodies, that a booster dose of a vaccine can produce, might not always work against the antigen but sometimes it can cause harm to the body itself.
“Such situations are known as Antibody-dependent Enhancement (ADE) under which the antibody, instead of preventing infection, starts helping the antigen infect more number of cells,” Dr Roy said.
“That’s why I am emphasizing the need for clinical data," he added.
Does high antibody prevent infection?
There is no denying the fact that a booster dose increases the level of antibody in an individual. However, there is no scientific evidence to suggest that the high antibody, acquired with the help of vaccines, can prevent infection from the variants of SARS-CoV-2.
Experts say that whenever a naturally infected person or a vaccinated person comes in contact with the virus, its antibody level shoots up as the body produces immunity for its protection. Since the vaccine also has dead viruses or parts of the virus, the body responds against this antigen and produces antibodies.
“Had high antibody helped in preventing transmission, fully vaccinated people or those with booster doses might not have been infected with Omicron. There is no study to find out the correlation between high antibody and its protection from infection,” Dr Sanjay Rai, Professor, Community Medicine in All India Institute of Medical Sciences (AIIMS), New Delhi.
There are 25 vaccines already approved by various authorities all over the world and 326 vaccines are currently at different stages of development. Dr Rai, who was a principal investigator of the Covaxin trial in AIIMS, said that any additional dose of a vaccine will enhance the antibody but its side effect needs to be measured.
“The main indicator should not be the increase in the level of antibody but its effectiveness in providing protection,” Dr Rai said.
Not enough study on the presence of memory cells
During the clinical trial, it was found that vaccines not only produce antibodies to fight against the virus but also produce memory cells. These cells help recognise the virus if it will try to enter the body in future.
So the antibody gradually declines and disappears after a few months but the moment a vaccinated or naturally recovered person comes in contact with the virus, these cells help produce antibodies once again to provide protection against the specific antigen.
After rolling out the universal adult vaccination, such studies haven’t been conducted on large samples size to find out the memory cell response in vaccinated individuals. A couple of studies with small sample size, like the one done by the Asian Institute of Gastroenterology in Hyderabad, have confirmed the presence of memory cells in vaccinated or naturally recovered people.
Well-known scientist and a member of the National Technical Advisory Group on Immunization (NTAGI) Dr Jayaprakash Muliyil is of the view that the boisterous response of an additional dose goes on to confirm the formation of the memory cell which produces antibody after identifying the same antigen.
“It shows that 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,” Dr Muliyil said.
“B cells and T cells in the human body memorize the antigen and the moment the same virus infects the body, they make antibodies specific to target the virus. That’s why reinfection is very low and even if it occurs, the severity is not as high as it was during the first infection,” he added.
Gyaneshwar Chaubey, a professor of genetics at Banaras Hindu University (BHU), agreed with Dr Muliyil. “Antibody starts declining after three months and the virus will continue to mutate. So after the third dose, we will start talking about the fourth dose and so on. So, instead of that, we should research on the aspects of the memory cell of people rather.”
Omicron hasn’t caused many deaths globally
As of now, there are around 3,000 confirmed cases of Omicron in over 60 countries but only one death has been reported in the UK due to its infection so far. Its symptoms are reported to be milder than all other variants present in the environment.
“How will you evaluate a vaccine against a variant which is neither causing hospitalizations or deaths? It has been conceded by manufacturers and experts that vaccines do not prevent transmission but only reduce hospitalizations and deaths and this variant is not causing any severity. So what endpoints or goalposts are you going to consider when testing a vaccine against this benign variant?” Dr Amitav Banerjee, a clinical epidemiologist at Dr D Y Patil Medical College, Pune, said.
Natural immunity provides better protection
Since the reinfection rate has been very low in the case of all the available variants of SARS-CoV-2, this tends to show that natural immunity, acquired after recovery from Covid-19, provides a better antibody than that of vaccines. The reinfection rate has been between 5 to 10 per cent.
Many public health experts say that despite the presence of Omicron in India, its transmission is very slow and there is no large outbreak witnessed anywhere yet.
“This is because a huge population in India has natural antibodies which can prevent transmission and stop the spread of the virus. Besides, they are being vaccinated as well. So, according to me, two doses of vaccine in India along with natural antibody provides far better protection as compared to three or more doses in other countries like USA etc,” Dr Banerjee said.
