June 7 (IndiaToday) – Covishield triggered more antibodies than Covaxin, claims a preprint of the first Indian study involving doctors and nurses who received both doses of either of the two Covid-19 vaccines. The study by Dr AK Singh and his colleagues states that both vaccines elicited a good immune response.
Unpublished data had earlier indicated that Covishield was found to be 70 per cent effective after the first dose. At the same time, preliminary data from its phase 3 trial put Covaxin’s efficacy rate at 81 per cent.
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“Among 515 healthcare workers (305 male, 210 female), 95 per cent showed seropositivity (higher antibodies) after two doses of both vaccines. Of the 425 Covishield and 90 Covaxin recipients, 98.1 per cent and 80 per cent, respectively, showed seropositivity,” says the study.
Antibody titer higher for Covishield than Covaxin
The study shows that while both Covishield and Covaxin prompted good immune response after two doses, seropositivity rates and median anti-spike antibody titre were significantly higher in the Covishield arm when compared to the Covaxin arm.
Antibody titer was 115 AU/ml (arbitrary units per millilitre) for Covishield and 51 AU/ml for Covaxin. A type of blood test, an antibody titer determines the presence and level (titer) of antibodies in the blood.
It goes on to add, “However, both the seropositivity rate and the average rise in anti-spike antibody were significantly higher in Covishield versus Covaxin recipients.”
Anti-spike antibody level is not the same as neutralising antibody titers (NAb). The two are not known to reliably correlate. In fact, neutralising antibody titers form only a fraction of the total anti-spike antibodies produced.
Gastroenterologist and former chief of the IMA’s Kochi unit, Dr Rajeev Jayadevan adds, “The percentage or level of anti-spike antibody measured in the study cannot be taken as a percentage of protection delivered to the recipient.”
Breakthrough infections
A total of 27 breakthrough infections (4.9 per cent) were recorded among respondents who had received both doses of either of the vaccines. Out of these, 25 were mild and two were moderate cases of breakthrough infections. No deaths were recorded as a result of breakthrough infections.
The study puts the risk of breakthrough infections in the case of Covishield at 5.5 per cent compared with 2.2 per cent for Covaxin.
While no difference was observed in relation to gender, body mass index, blood group and any comorbidities, people aged 60 years and above or those with type 2 diabetes had a significantly lower seropositivity rate, indicating a comparatively lower antibody response.
Study underlines need to ramp up vaccinations
Both vaccines were seen to be providing excellent protection on the ground, according to reports from doctors across the country. The exact percentage, say the authors, will only be seen in a head-to-head trial.
The study also shows a good safety profile for both vaccines. By and large, the study shows that the vaccines are working. It further underscores the need to speed up vaccinations to avert a potential third wave of infections by expanding the coverage of vaccinations.
At present, less than four per cent of the Indian population has received both doses of either of the vaccines, while less than 15 per cent have received at least one dose.
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