Feb 11, 2021
In this episode: Effect of Israel’s full bore vaccine program, protection after a single vaccine dose, immunity after a single dose in those with COVID antibodies from previous infection, evidence of decreased transmission following AstraZeneca vaccine, vaccine potency and viral variants.
We Discuss:
Israel’s full bore vaccination
program and the effect on new cases, hospitalizations, and severe
disease [00:01:18];
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In patients over 60
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41% Decrease in new cases
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31% decrease hospitalizations
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24% decrease critically ill
How much protection is there
after a single dose of mRNA vaccine? [00:04:56];
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Pfizer vaccine reduced infection 13-24 days after first vaccination by 51% compared to 1-12 days after infection
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Inflection point 18 days post vaccination
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This doesn’t mean to get one shot and be done, but gives insight on immunity following first vaccine dose and when it arises
Effect of a single vaccine dose
on those who have pre-existing COVID immunity
[00:07:00];
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109 people getting vaccinated divided into two groups.
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Those with and without SARS-CoV-2 immunity/seropositive vs seronegative for SARS-CoV-2 immunity IgG.
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Seropositive patients’ antibody response to the first vaccine was equal to or even exceeded the titers found in naive/seronegative individuals after a second dose. In other words -- one vaccine in this study led to a higher antibody level than those who didn't have existing immunity and got two shots .
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Antibody titers in those with previous covid/seropositive who got a shot had up to 10 fold the antibody levels compared to those who were COVID naïve/seronegative (see below graphic)
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This preliminary data also suggests that those with previous immunity didn't get much of an antibody bump after the second dose .
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Is the second dose worth it in those with previous immunity? Well, first immunity needs to be proven by blood testing. Using an intense reaction to the first vaccine is a poor man’s marker of previous immunity, but that’s not what this study looked at.
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Immunologists are divided on what to do here. Some say a second dose isn’t necessary if there are COVID antibodies prior to inoculation (or there is a strong reaction after first shot in those with a previous history of infection) while others cite the data- the studies look at a 2 shot program, so stick with that
Graphic
from Krammer, Florian, Komal Srivastava, and Viviana Simon. "Robust
spike antibody responses and increased reactogenicity in
seropositive individuals after a single dose of SARS-CoV-2 mRNA
vaccine." medRxiv
(2021).
Evidence that the new Oxford
AstraZeneca vaccine decreases asymptomatic infection and
transmission [00:12:11];
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Study participants regularly swabbed after vaccination
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The vaccine group had up to 67 percent fewer positive swabs suggesting decreased asymptomatic infection and transmissibility
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Study results also call into question dosing between shots
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Interval between shots and vaccine efficacy
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Under 6 weeks, 55% effective
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12 weeks, 82% effective
Vaccine potency against UK and
South African variants [00:16:06];
Why you shouldn’t plan a
hootenanny quite yet, even if you’ve had 2 shots of vaccine
[00:17:00];