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.
2/10
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.
3/10
Cont’d
In other words, the pie chart will give a true picture only if (theoretically) indefinite follow up occurred in the three subgroups (partially and fully vaccinated, unvaccinated) so they get equal chance to be exposed to infection on a timeline.
4/10
Cont’d
Hence it is important to factor in this lead-time bias while reading such pie charts that are done during an ongoing vaccination process, regardless of the place it is done at.
This also applies to the early data that came out of Israel.
5/10
Cont’d
To illustrate this bias with an example, imagine you are calculating the risk of a road accident based on 3 groups of drivers based on their age.
Your question is whether older age groups have a lower risk of accidents.
6/10
Cont’d
To do the study properly, you must ask each group to drive for the same DURATION and DISTANCE in SIMILAR conditions.
But if you ask the older group to only drive 10 Km, middle-aged group 100 km and the youngest group 1000 km, you can’t compare the accident rates.
7/10
Cont’d
In this hypothetical study, we will come up with an erroneous conclusion that older people are much less likely to have accidents. This result could occur simply because the older people did not drive long enough, and not because they were necessarily safer drivers.
8/10
Cont’d
A potential solution would be to calculate “man-days of exposure” and then redo the pie chart based on number of days of exposure, and the % infections acquired between the three subgroups.
9/10
Note: This thread was made only to highlight a common bias that occurs while reporting breakthrough infections, and it does not take anything away from PGI for publishing their data.
The study does indicate that unvaccinated people are more likely to pick up infection.
10/10
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It is not a straightforward process like deciding between 'pregnant & non-pregnant'. It is easy to under-count (a frequent complaint), and also over-count.
Let's take a look at WHO, ICMR & Public Health England's definitions. See thread.
1/9
2/9 (see whole thread)
This is the WHO's definition of COVID-19 death.
It was written on 16 April 2020, at a time when the complete picture of COVID-19 was not known.
We now know that COVID-19 is much more than a viral illness; delayed deaths occur.
These delayed deaths may follow a period of apparent clinical recovery, that is when the patient feels better.
The ongoing immune process inside the body could last for weeks, when vascular events such as stroke, heart attacks and pulmonary emboli have been well-described.
Rare study that demonstrates long-lived plasma cells (that make antibodies) in the bone marrow of those who recovered from COVID-19, after 7-11 months.
-This study looked the body's ability to generate antibodies long-term.
-We know that S-specific antibody levels in blood drop for about 4 months, & then level off.
-That however does not mean we 'lost' the ability to make antibodies.
-Let us look @ some basics first.
3/13
-During infection, B cells pick up the antigens of the virus and present them on Class II MHC to CD4 T cells in the germinal centres in lymph node or spleen. This activates B cells, generating memory cells and plasmablasts. Some of these mature into long-lived plasma cells.
This study involved 36,659 HCW who had easy access to testing, was done during a surge and involved relatively younger people.
Of these, 28,184 completed 2nd dose by the time of publication, of these, 14,990 were 2 weeks past 2nd dose.
See research letter attached above.
2/2
We must also remember that the age profile of this cohort is young; their baseline risk of developing severe disease is relatively low. The key point in this study is that they had some level of mandatory testing, which means lower chance of missing infections.
3/3
From Doctors, to Doctors.
25 Practical Tips for Doctors Treating COVID-19.
These pearls are based on the collective experience of several doctors who have been meeting every Tuesday 8 PM @ IMA Cochin, ever since the pandemic started.
Surge in Vietnam 🇻🇳 coincides with the discovery of B.1.617.2 with an additional mutation: Y144 deletion which had been seen in various settings (B.1.1.7 variant, and also in immunosuppressed patients who harboured longer SARS-CoV-2 virus infections)
Multiple mutations occurred while the SARS-CoV-2 virus lived for a long time in a immunocompromised B-cell-depleted patient. Such studies provide a rare opportunity to follow viral adaptive evolution. The Y144 deletion was first spotted ~a year ago.