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  • Rob Orman

40. Effect of a single vaccine dose with and without previous COVID infection

In this episode: Impact 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.


Listen on:



We Discuss:


Israel’s full bore vaccination program and the effect on new cases, hospitalizations, and severe disease [00:01:18];

  • In patients over 60

  • 41% Decrease in new cases

  • 31% decrease hospitalizations

  • 24% decrease critically ill

  • Article Link

How much protection is there after a single dose of mRNA vaccine? [00:04:56];

  • Pfizer vaccine reduced infection 13-24 days after first vaccination by 51% compared to 1-12 days after infection

  • Inflection point 18 days post vaccination

  • This doesn’t mean to get one shot and be done, but gives insight on immunity following first vaccine dose and when it arises

  • Article Link


Effect of a single vaccine dose on those who have pre-existing COVID immunity [00:07:00];

  • 109 people getting vaccinated divided into two groups.

  • Those with and without SARS-CoV-2 immunity/seropositive vs seronegative for SARS-CoV-2 immunity IgG.

  • 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 .

  • 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)

  • This preliminary data also suggests that those with previous immunity didn't get much of an antibody bump after the second dose .

  • 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.

  • 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

  • Article Link


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];

  • Study participants regularly swabbed after vaccination

  • The vaccine group had up to 67 percent fewer positive swabs suggesting decreased asymptomatic infection and transmissibility

  • Study results also call into question dosing between shots

  • Interval between shots and vaccine efficacy

  • Under 6 weeks, 55% effective

  • 12 weeks, 82% effective

  • Article Link


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];


And not much more.


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