The latest COVID-19 guideline from Directorate General of Health Services at Ministry of Health & Family Welfare @MoHFW_INDIA, are pristine no-nonsense science.
Antibody titre 115 AU/ml for Covishield and 51 for covaxin.
27 breakthrough infections occurred (4.9%) after both doses: 25 were mild, 2 were moderate, no deaths.
Risk of breakthrough infection:
5.5% with covishield
2.2% with covaxin
2/5
Listing some facts which will help understand the context of the study:
1. Anti Spike antibody is not the same as neutralising antibody. Its level is not known to reliably correlate with NAb, which is typically measured only in research labs. See my earlier tweet on this.
3/5
The neutralizing ability of vaccine drops with time, and age. The variants of concern B.1.617.2, B.1.351
and B.1.1.7, have a 5.8, 4.6 and 2.6 - fold reduction respectively when compared with the original Wild type strain. Study from UK comparing variants against vaccines.
The study measured neutralizing ability of post-vaccine serum against variants. Theoretically, it means VOC are more likely to get past vaccine protection, esp. those who had only 1 dose.
However, such lab studies are best interpreted along with clinical observations.
2/5
The reason for seeking clinical correlation is that immunity is multi-pronged, and we are not measuring T cell protection in such studies.
While neutralizing antibodies stop the virus from infecting our cells, what happens AFTER the infection is largely decided by T cells.
3/5
Among 506 healthcare worker infections from a cohort of 12,248 at PGI Chandigarh, 64% were unvaccinated, 9.5% were fully vaccinated (>2 weeks past II dose)
However, the shorter follow up post 2nd dose (time bias) means the real % could be higher.
The graph does not factor in the duration of follow up. During an ongoing vaccination process, those who are unvaccinated “get longer time” (compared to the vaccinated healthcare workers) to pick up the infection.
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Cont’d
Since vaccination takes time, those who were 2 weeks past second dose in the pie chart would have had fewer days of observation, than others.
This means that the odds of picking up infection will be smaller by default. This also gets reflected in the pie chart.