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.
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];
And not much more.
If you like what you hear on Stimulus and use Apple/iTunes as your podcatcher, please consider leaving a review of the show. I read all the reviews and, more importantly, so do potential guests. Thanks in advance!
Interested in sponsoring this podcast? Connect with us here
Follow Rob: Twitter: https://twitter.com/emergencypdx