Covaxin tested against two variants B.1.617.2 (India) & B.1.351 (S Africa). Mild reduction in neutralization ability noted; 2.7 and 3-fold, which is a smaller loss compared to other vaccines, reports ICMR/NIV study.
See graph for comparison.
Thread. 1/n biorxiv.org/content/10.110…
Neutralizing ability is one of the parameters scientists use to measure a vaccine's firepower against a virus.
If the vaccine is very effective, then its ability will be 1 or close to 1 -that is, in comparison with how effective the same vaccine was against the old virus.
2/12
If the virus has become so smart, it will then take several times the original "neutralising power" to kill it.
e.g. If the amount of vaccine required to kill the new variant is 10 times what it took to kill the old virus, we say the neutralising ability is 10-fold lower.
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Thus, if the vaccine is relatively more effective against the variant, then the neutralising ability is perhaps only 1-fold or 2-fold lower.
Knowing this is important when we try to interpret lab studies on vaccines and variants, hence the plain English explanation.
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In this study, ICMR/NIV scientists have found that the GMT (Geometric mean titer) of the vaccine sera were 187.5, 61 and 68.9 against B1 (original), B.1.351 (S. Africa) and B.1.617.2 (Delta, India) respectively.
5/n
Antibody titers were defined as the highest serum dilution that resulted in >50% (PRNT50) reduction in the number of plaques grown.
The more number of times dilution occurs, the less the antibody in the serum. A powerful vaccine can therefore be diluted MORE no. of times.
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The neutralizing antibody titer is the reciprocal of the highest dilution that still achieved the result discussed above.
Thus, if the serum was able to be diluted 1/64 times, the titer is 64. If it was diluted further 1/512 times, the titre is written as 512.
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Since these dilutions are multiples, logarithm is used for comparison, because numerically the difference between 256 & 512 seems more than between 4 & 8, even though they represent successive dilutions.
As arithmetic mean is misleading, geometric mean GMT is used here.
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Back to the study; see the whole thread for references about various vaccines and their neutralising ability against B.1.351 variant (chosen here because it has two critical mutations E484K and N501Y among others). Please remember they are not from the same lab.
While reading studies on the topic, it is important to keep some of the following points in mind:
1. Studies done in different labs may not be comparable head-to-head
2. Neutralisation or antibodies only measures a fragment of the immune response generated by vaccine.
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3. There are multiple segments to our immune response that cannot be measured.
4. Heterogeneity is the rule for this virus, there is considerable person-to-person variation in our immune response to this virus and to vaccination; not all of that can be measured in labs.
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*serum generated by a powerful vaccine can be diluted (read as)
[Tweet shortened due to word limit]
Sinopharm, study by Huang et al is linked, not Moderna
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Traditionally we hear about virus entering the exposed surface of the cell, like a bug flying in through the open window of a multi-apartment complex.
Now, imagine this bug burrowing through the walls into all the neighboring units. That essentially is cell-to-cell entry.
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The problem with this process is that our neutralising antibodies might not be able to stop it.
These antibodies are designed to stop the bug from entering through the window, but not from burrowing through the walls between adjacent apartments.
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ICMR-NIV study on P.2, the variant originally found in Brazil since ~April 2020 (WHO). Also called B.1.1.28.2 or zeta, it is now being rapidly replaced by P.1 in Brazil.
ICMR/NIV observed its effects on hamsters in comparison with P.1.
Presenting some context first. This variant P.2 was only seen in 2 samples so far in India; from asymptomatic travelers who arrived from Brazil and UK.
In Brazil, it is also being phased out by P.1 (deeper colour in recent weeks of 2021, genomic data from Manaus, Brazil).
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Study from Brazil showing how P.2 is being phased out by P.1. The latter variant has the N501Y mutation in addition to E484K, among several others.
Traditionally D-dimer is elevated when there are fibrin degradation products associated with clots. But D dimer is also elevated in other inflammatory conditions, trauma, post-op state / malignancy.
In COVID-19, its role is primarily as a marker of severity & inflammation.
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Studies in COVID-19 patients have shown that unless there are specific clinical pointers to a clot (leg or lung), an elevated D-dimer value ALONE will not be worth pursuing: we might end up chasing a bird that was never there.
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
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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.
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