I doubt there's been a sudden influx of med related workers. I suspect the Bay Area's universities, pharmaceutical, and biotech companies have created a slow influx over time. Like tech, a long slow one. Because a large chunk of "tech" is medical related.
It's worth excluding the lab techs, genetic counselors, admins, etc., from the medical field if you're going to exclude the non-engineers from the tech field. It makes for a more apples to apples comparison.
I couldn't give a percentage, but there are a lot of biotech companies in the peninsula, especially in South San Francisco, and Kaiser Permanente is one of the largest employers in the area. UCSF and Stanford Medical Center are also major employers.
It's worth excluding the lab techs, genetic counselors, admins, etc., from the medical field if you're going to exclude the non-engineers from the tech field. It makes for a more apples to apples comparison.