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Stimulus.


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];
  • In patients over 60
  • 41% Decrease in new cases
  • 31% decrease hospitalizations
  • 24% decrease critically ill
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
 
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
 
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
 
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];