Bhubaneswar: COVID antibodies start declining after two months in recipients of Covaxin and after three months in those vaccinated with Covishield.
This was reported in a recent study led by ICMR-Regional Medical Research Centre (RMRC), Bhubaneswar.
The study commenced in March this year and was undertaken to determine the most common antibody IgG (Immunoglobulin G) among fully-vaccinated healthcare workers in the state.
According to ICMR-RMRC scientists, samples from 614 fully vaccinated healthcare workers were collected for the study. The participants comprised 308 (50.2 per cent) Covishield and 306 (49.8 per cent) Covaxin recipients. Eighty-one participants reported breakthrough cases (COVID infection even after full vaccination).
A total of 257 participants had contracted the infection before being vaccinated. Among them, 33 were reinfected after two shots of the vaccine.
The samples were collected from Berhampur, Khurda and Burla.
Talking to Odisha Bytes, ICMR-RMRC scientist Dr Devdutta Bhattacharya said this does not mean that a person in whom the antibodies have declined is prone to infection. “Memory cells develop due to natural immunity after the infection and vaccine-based immunity and these protect the body against the virus,” he said.
“Just the way we remember a place once visited, the memory cells persist and provide the required protection,” he said, adding, no vaccine provides lifetime protection.
Bhattacharya further said a vaccine shot after infection triggers the antibody level in the body. “It is the same in breakthrough cases and the body produces much more antibodies. The infection post-vaccination acted as a booster in these 81 cases,” he said.
According to the study, the production of vaccine-induced IgG antibodies is significantly higher in Covishield compared to Covaxin. In seronegative individuals, the rate of seroconversion after 28 days of the first dose was 81.9 per cent for Covishield and 16.1 per cent for Covaxin.
The results of 533 individuals without any history of infection post-vaccination indicated a significant drop in spike RBD IgG concentration for both vaccines.
He, however, was quick to point out that the vaccines are working fine and the severity is much less in such cases. “It neutralises the virus and help in clearing it from the body,” he said.
The scientist, however, said that studies are on to know the threshold level of antibodies for protection against COVID. “We should not think of booster dose until the entire population is fully vaccinated,” he added.
Besides RMRC, researchers from Chest Clinic, Berhampur; Kalinga Institute of Medical Sciences, Bhubaneswar; MKCG Medical College, Berhampur; Institute of Life Sciences, Bhubaneswar and Veer Surendra Sai Institute of Medical Sciences and Research, Burla were also part of this study.
Assistant Professor of Transfusion Medicine at MKCG Susmita Behera said samples of health workers were sent from 0-day, which is prior to vaccination, and the next 5 months. “Though a few breakthrough cases were hospitalised for lower respiratory infection, no one was put on a ventilator. Health workers are also getting reinfected before of longer duration of exposure,” she said.
Behera, however, advocated the need for a booster dose. “It is difficult to say how long the memory cells will provide the needed protection,” she added.
Director of ICMR-RMRC, Bhubaneswar, Sanghamitra Pati told the media that the study will be followed up after six months and there are plans to continue this over a period of time.
She said that study has a follow-up plan for two years, which will further help in understanding the kinetics model and also provide a better estimate of the antibody response in both seropositive and seronegative individuals over a significant period.
“Only after such studies, it can be determined whether a booster shot for those fully vaccinated is required or not and if required, when,” she added.
