And they were still peddling this message decades later.
The Watchtower 1st November 1961 p.670:
Since the Bible forbids the eating of blood, how are Christians to view the use of serums and vaccines? Has the Society changed its viewpoint on this? - J. D., U.S.A.
The Bible is very clear that blood could properly be used only on the altar; otherwise it was to be poured out on the ground. (Lev. 17:11 - 13) The entire modern medical practice involving the use of blood is objectionable from the Christian standpoint. Therefore the taking of a blood transfusion, or, in lieu of that, the infusing of some blood fraction to sustain one's life is wrong. As to the use of vaccines and other substances that may in some way involve the use of blood in their preparation, it should not be concluded that the Watch Tower Society endorses these and says that the practice is right and proper...it is a contamination of the human system."