We're still waiting on the science about that.
Insofar as published, peer reviewed studies, yes, we are still waiting. However, the CDC can, will, and does work off preliminary data as well.
The basic question at hand is this: in creation of the vaccines, the basic test of effectiveness was "prevent you from becoming ill", meaning, showing symptoms. It left open the question of whether a vaccinated person could be infected, but not be ill, and thus possibly spread the virus.
In early April, the
CDC published a preliminary report, tracking health care workers, first responders, and other front line personnel.
"Among unvaccinated participants, 1.38 SARS-CoV-2 infections were confirmed by reverse transcription–polymerase chain reaction (RT-PCR) per 1,000 person-days. In contrast, among fully immunized (≥14 days after second dose) persons, 0.04 infections per 1,000 person-days were reported, and among partially immunized (≥14 days after first dose and before second dose) persons, 0.19 infections per 1,000 person-days were reported. Estimated mRNA vaccine effectiveness for prevention of infection, adjusted for study site, was 90% for full immunization and 80% for partial immunization. These findings indicate that authorized mRNA COVID-19 vaccines are effective for preventing SARS-CoV-2 infection, regardless of symptom status, among working-age adults in real-world conditions."
The results were simple - the vaccines are not just 90%+ effective at keeping you from getting ill, they are 90%+ effective at keeping you from getting infected at all. And if you are not infected at all, you cannot spread the virus.
It is now a month later, and as far as I can find, subsequent data has only supported this result. The data is still preliminary, because the rate of infection is terribly low, and in very technical statistics, that leads to a broad confidence interval around that 90%.
And, now here's a place where human understanding of risk typically fails us. Once you have a method that is highly effective as preventing infection/transmission, layering on more methods only adds marginal benefit.
If you have two, independent methods of prevention, that are each 50% effective, if you use them both, the result is about 75% effective, which seems like a good deal.
If you have two independent methods of prevention, one is 90% effective, and the other is 50% effective, the result is about 95% effective.
Now, let us apply what that effectiveness really means. A 90% effective vaccine does not mean it leaves you with a 10% chance of getting covid. It means your chance of getting covid is 90% less than if you were not vaccinated.
Broadly speaking, the chance of catching covid is on the order of 1% per exposure. A 90% effective prevention reduces that to 0.1% chance. A 95% effective prevention reduces that to 0.05% chance per exposure.
So, basically, adding the mask only drops the chance of transmission by
five hundredths of a percent.
That's a small change in probability, down in the level of experimental error where it is apt to be wiped out by other factors, such as to be meaningless.
That is not to say you should not wear a mask. I support anyone who wants to wear a mask. I will be happy if my state retains its "masks must be worn indoors in public places" mandate. I'm going to continue avoiding certain venues, and wearing masks myself.
