NotFormer, I was only 1 when that change was made. Some older witnesses from the pre-1953 time period were still alive then and did not seem to get the message, so it had to be made very, very clear. Vaccinations were allowed around 1950, but the WTS was very coy about revealing that. That is why this was changed in 1952. "
● Is vaccination a violation of God’s law forbidding the taking of blood into the system?—G. C., North Carolina.
The matter of vaccination is one for the individual that has to face it to decide for himself. Each individual has to take the consequences for whatever position and action he takes toward a case of compulsory vaccination, doing so according to his own conscience and his appreciation of what is for good health and the interests of advancing God’s work. And our Society cannot afford to be drawn into the affair legally or take the responsibility for the way the case turns out.
After consideration of the matter, it does not appear to us to be in violation of the everlasting covenant made with Noah, as set down in Genesis 9:4, nor contrary to God’s related commandment at Leviticus 17:10-14. Most certainly it cannot reasonably or Scripturally be argued and proved that, by being vaccinated, the inoculated person is either eating or drinking blood and consuming it as food or receiving a blood transfusion. Vaccination does not bear any relationship to or any likeness to the intermarriage of angelic “sons of God” with the daughters of men, as described in Genesis 6:1-4. Neither can it be put in the same class as described at Leviticus 18:23, 24, which forbids the mingling of humans with animals. It has nothing to do with sex relations.
Hence all objection to vaccination on Scriptural grounds seems to be lacking." WT 1952 December 1952, p. 764
(BTW, I knew some jws long after 1952 were still telling other jws that vaccinations were not allowed, probably why the WTS had to make it very clear that they were allowed, especially during the pandemic.