It will not be 100% efficient, but reduction can be achieved.
Experts on the matter (I read a book recounting smallpox research, not a domain expert myself [0]) were concerned more about the publishing of that research than about the research being done, since proliferation is deemed very easy in the field. You don't need resources as with nuclear weapons to reproduce research like that.
(Edit: typo)
[0] The Demon in the Freezer by Richard Preston
An 80% kill rate of mice that are genetically engineered to express human ACE genes. For comparison, the original SARS-CoV-2 strain killed 100% of those humanised mice. Those rates aren't the same among human populations.
It was a modified version bringing the kill rate down from 100% to 80% in lab mice specifically bread to be weak to this virus.
It is when literally this week a version with an 80% kill rate but with the spread of the most transmissible was made in a lab for no good reason.
How many would die if that leaked out and the only reason it’s been made is just so some academic can get their name in a paper and earn some grant presumably.
The idea of we just have to trust that these labs are secure and competent enough when the fact they’re even making something so deadly raises questions about their competence. We need to start judging the people making these things with the potential to kill millions the same as we would anyone else building something that had the potential to kill millions.
I don’t see why playing with Weapons of Mass Destruction in a random lab is just considered fine when the weapon is invisible and can live inside your body or a mouse. At least Fat Man and Little Body couldn’t be carried off base by a single person.