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I do love me some scientific serendipity. While everyone is talking about whether it may be safe+effective to give people only half the dose of the new #COVID19 vaccines, @TheLancet just pubbed a study looking at this same idea with the yellow fever vaccine 
First and foremost, the yellow fever vaccines and the COVID-19 vaccines are NOT directly comparable. YF vaccines are a live attenuated vaccines, meaning they are composed of actual YV viruses that have been rendered non- or less- infectious.
The Pfizer/BioNTech and Moderna vaccines are pieces of mRNA that instruct cells to produce a protein with the same sequence and structure as one particular part of the virus, which teaches the immune system to recognize and attack the virus if exposed.
Also, the YF vaccines are given in one dose, whereas the COVID-19 vaccines are supposed to be given in two doses, spaced a few weeks apart.
With that in mind, the authors found that just 1/5th the standard dose of the YF vaccine was "non-inferior to the standard dose in inducing seroconversion 28 days after vaccination", a very cautious way to say the lower dose produced anti-viral antibodies https://doi.org/10.1016/S0140-6736(20)32520-4
More serendipitous, @thelancet also pubbed the results of the @AstraZeneca COVID19 vaccine. In this trial, a portion of patients *accidentally* received a half the amount of vaccine in the first dose (still got full amount at second dose) https://doi.org/10.1016/S0140-6736(20)32661-1
They found that this low initial dose (in combination with a second full dose) was actually **more** effective than the two full doses. The data also support the idea that there is short term protection after one dose.
Now, very critically, does that mean that we are safe to give only one of two doses of the COVID vaccine? Not at all. But I'm curious if there is a general belief in the field that more is always better/necessary or how/why this two dose regime was selected
Also very critically, this science is all so fresh and so much more work is needed to really understand what is happening with this incredibly complex immune response. Lastly, this is just my personal interpretation of the studies.
HT to @LauringLab for posting this article. How do you interpret these findings? Is there a larger precedent for this in the field?
