This is extremely promising. A new study conducted by Pfizer and Israel’s Health Ministry shows Pfizer’s vaccine was estimated to be 89.5% effective at preventing SARS-CoV-2 infections regardless of whether symptomatic or not. This infers a possible reduction in transmission! 🧵
Study is based on real-world data and analysis of individuals vaccinated with their 2nd dose.
90% Drop in infection
94% against symptomatic infection
94% against severe/crit. hospitalization
93% against death
This study can be found here (just see the screens).
The next two studies I want to highlight take into account viral load. When an infected individual has a high viral load, they are more likely to shed more viral particles, hence transmit the virus. Higher viral load is usually associated with severe disease as well. Carrying on.
In this second study, researchers traced the Ct value distribution of 16,297 positive qPCR tests and discovered a decrease in viral load in the >60yr old population post vaccination. The increase we see here in average Ct values over time demonstrates sharply reduced viral load
once the vaccine had time to take effect (an increase from ~26.5 to ~27.5 corresponding to a reduction of 50% in mean viral load overall). This provides us with evidence that the vaccine may indeed be reducing viral loads.
This study can be found here:…
Lastly, a third study analyzed Ct levels from positive PCR tests and performed a direct comparison of viral loads in vaccinated vs. unvaccinated individuals. First, researchers plotted the Ct levels indicating viral loads of 2897 individuals infected after their first dose
as a function of days since first dose. Remember, positive PCR tests after the first dose and before the second dose can occur while your body works to establish immunity (immunity is not instantaneous!) Note that 2897 infections out of 650,000 vaccinated corresponds to an
infection rate of 0.45% which is considerably lower than the infection rate in the Israeli population during the time of this study. Data plotted from their PCR tests shows the vaccine reduced viral loads 4-fold starting 12 days after the first dose with a change in mean Ct going
from 25 to 27. This type of reduction in viral load suggests these individuals would be much less likely to transmit the virus to those around them based on what we currently know linking viral load and transmission of SARS-CoV-2. To assess whether the vaccinated individuals had
lower viral loads than the unvaccinated individuals, they then compared the distribution of Ct in unvaccinated infected vs. those infected in days 1-11 after first vaccine dose (N=1755) and those infected days 12-28 after their first vaccine dose (N=1142).
The distribution of viral loads in those infected in days 1-11 after their first vaccine dose were identical to those infected in the unvaccinated group, but the viral loads of those whose infection was detected on days 12-28 after first dose were systematically lower than those
in the unvaccinated group, again by a factor of about 4x.
This study can be found here:…

All together, data from these studies provide probable evidence that Pfizer’s
vaccines may indeed provide substantial protection against infection and reduction of transmission once that first dose kicks in. Further transmission studies will need to be conducted but it’s a very good start nonetheless!
Another study to add to this thread. Pfizer’s vaccine demonstrates substantial early reductions in SARS-CoV-2 infection and symptomatic COVID-19 rates following first dose (VE 89–91% during days 15–28 after first dose) which might help with delayed doses.…

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More from @sailorrooscout

20 Feb
Vaccines are preventives, not cures.
The purpose of vaccination is to bring the severity level down to that of a benign virus. That’s how this works. Our best protection is to keep cases low and get people vaccinated. To expect eradication of this virus right now is unrealistic.
With this said, the more people vaccinated, the more restrictions should start to be lifted. Why? We are already starting to see evidence these vaccines do prevent transmission the more data comes out; it would be extremely ignorant to suggest otherwise or disregard it.
Eradicating this virus right now from the world is a lot like trying to dig a tunnel to the center of the Earth using only a plastic spoon. It’s unrealistic. Some forget or simply don’t care (totally different virus) but Polio was endemic before it was 100% declared eradicated.
Read 12 tweets
18 Feb
For those of you in the UK, this is wonderful news! Real-world data from the UK’s vaccine rollout program revealed just one dose of Oxford/AstraZeneca’s or Pfizer’s vaccines appear to block transmission and infection by two-thirds regardless of age group!…
And if you’d like some more good news: AstraZeneca has confirmed 100% protection against severe disease, hospitalization and death in their primary analysis of Phase III trials more than 22 days after the first dose. The trials were done in the UK, Brazil AND South Africa.
Increased efficacy with longer inter-dose interval, protection of over 70% starting after a first dose and first indication of reduction in disease transmission of up to 67%.… and…
Read 4 tweets
17 Feb
Ready for some good news?

Lab studies suggest Pfizer’s and Moderna’s vaccines CAN protect against SARS-CoV-2 variants B.1.351 and B.1.1.7. Despite reduction, neutralizing titer levels with B.1.351 remain above levels that are expected to be protective!…
In addition, they found NO reduction in efficacy against the B.1.1.7 variant! It’s a good day!
Preliminary reports can be found here:
Wanted to share more this morning concerning safety and efficacy of these vaccines that might put some of you with delayed Pfizer doses at ease. One dose of Pfizer’s vaccine was found to be highly efficacious, with a vaccine efficacy of 92.6%, similar to the first-dose efficacy
Read 5 tweets
17 Feb
I want to bring this up. I’m sure by now you have seen those sensationalist headlines about variants merging and “heavily mutated hybrids” and what not. Guess what I want you to do right now? Ignore them. Yes, ignore them. Know why? Things like this are just mass hysteria.
The ones we need to be paying attention to are B.1.1.7, B.1.351 and P.1 because these are the only known SARS-CoV-2 variants that HAVE been shown to possess any evidence of functional significance or biological properties that make them a cause for concern to date. The rest?
Forget them. I read one article and I quote: “the recombination event may have occurred within the sample after it was taken from the infected person, not while it was inside their body. In which case it is an accidental laboratory artefact, not a wild virus.” Makes my head hurt.
Read 6 tweets
17 Feb
A new study out of Harvard offers evidence that SARS-CoV-2 variant B.1.1.7’s increased transmissibility isn’t due to its viral load but rather it’s delayed clearance, resulting in longer duration of infection. The implications are extremely positive. 🧵…
This could potentially mean a longer personal isolation period (longer than the currently recommended 10 days after symptom onset) may be all that is needed to control the spread of B.1.1.7!
For individuals infected with B.1.1.7, the mean duration of the proliferation phase was 5.3 days, the mean duration of the clearance phase was 8.0 days, and the mean overall duration of infection (proliferation plus clearance) was 13.3 days.
Read 5 tweets
17 Feb
Let’s discuss SARS-CoV-2 variants, selective pressure, and mutations. In the face of variants, our best protection is to get more people vaccinated. Vaccination will not automatically select for vaccine-resistant variants, especially if we can reduce transmission. Here’s why. 🧵
First, it is important to realize these vaccines will not drive the emergence of new variants and compel this virus to mutate in novel ways (OR create some scary super mutant so throw that idea out the window). I think this where a lot of the confusion lies- it’s not possible.
The specific mutations we are currently witnessing focus on altering the fitness of this virus by improving its rate of transmission with some signs of immune evasion. Mutation is a fairly constant process to begin with. It occurs randomly when a virus replicates and trust me,
Read 14 tweets

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