Covaxin booster dose generates 25-fold rise in antibodies: ICMR study

The year-long longitudinal cohort study started in January last year and continued till March this year. A total of 304 healthcare workers (HCWs) were included in the study.
Image used for representational purpose. (Photo | AP)
Image used for representational purpose. (Photo | AP)

BHUBANESWAR: In a first-ever study in the country, researchers have found the long-term effect of Covid antibodies in people who have taken the Covaxin vaccine, and people with booster breakthrough had mild symptoms and did not require hospital admission.

The study by ICMR’s Regional Medical Research Centre (RMRC) here that investigated the year-long longitudinal antibody responses and the dynamicity in Covaxin and Covishield recipients revealed the former performed better even as both the vaccines effectively induced humoral responses.

“We found Covaxin can boost around 25-fold in IgG titre level whereas the Covishield booster spiked three-fold in participants who never had Covid-19 history. Both the vaccine boosters were able to develop neutralising antibodies at a 92 pc inhibitory level,” senior scientist and in charge of Cobas Laboratory and antibody testing at RMRC, Dr Debdutta Bhattacharya said.

The administration of homologous booster dose had increased both the spike and neutralising antibodies after one month of the administration, he added.

The year-long longitudinal cohort study started in January last year and continued till March this year. A total of 304 healthcare workers (HCWs) from six different hospitals, healthcare facilities and research institutes in Odisha were included in the study.

Among 304 HCWs, 154 (50.7 pc) people took Covaxin and 150 (49.3 pc) received the Covishield vaccine. The seroconversion rate after one month of complete dose was 68.3 pc in the Covaxin group versus 95.8 pc in the Covishield group.

The study found significant differences in antibody responses among the two vaccines.

The antibody titre of 190 HCWs without any post-vaccination Covid-19 history showed a significant waning at the end of 10 months after double dose vaccination.

The persistence of IgG was higher and the difference was statistically significant in the 45-59 years age group as compared to 18-44 years among Covaxin recipients.

The waning of antibody was non-significant among the people above 60 years in Covishield receivers.

During the year-long follow-up, 114 (37.5 pc) HCWs were infected by SARS-CoV-2 after double dose of either vaccine where 78 (68.4 pc) were Covaxin and 36 (31.6 pc) were Covishield recipients. The median day of these breakthrough cases was calculated as 77 days post double dose vaccination.

Among the vaccine breakthrough cases, 233 HCWs had mild symptoms, seven were hospitalised, none required ventilation and no death was recorded.

A total 48 (32.9 pc) booster recipients were infected with coronavirus at least 15 days after the booster dose and 13 (8.9 pc) of them were categorised as re-infection.

Of these 48 recipients, 23 (47.9 pc) were administered Covaxin and the rest 25 (52.1 pc) with Covishield. Most of them had only fever as primary symptoms followed by fatigue and cough. None of them required any hospital admission.

Among the 48 booster breakthrough cases, all were infected with the Omicron variants.

The study found a negative neutralising antibody percentage in participants, who got infected with the virus after a booster dose. However, the level of neutralising antibodies was 56.2 pc and 58.6 pc for Covaxin and Covishield respectively at the time of infection after the booster dose.

“The findings can help to implement vaccination strategies, particularly the need for a booster dose of the present vaccines. It could also aid in speculation about the requirement for more potent vaccine options or vaccine mandates to minimize vaccine escape.

The use of mixed or heterologous vaccines as boosters can also be studied to evaluate the correlates of protection and sustainability of longer antibody responses,” Dr Bhattacharya said.

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