Thread by @sailorrooscout

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
Effectiveness:
94% against symptomatic infection
94% against severe/crit. hospitalization
93% against death
This study can be found here (just see the screens).

https://twitter.com/nadav_eyal/status/1362405662509068289

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:
medrxiv.org/content/10.110…

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:
medrxiv.org/content/10.110…

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.
thelancet.com/journals/lance…