The strictest of measures are taken to guard against any contamination during the production of vaccines. This is one of the most heavily-regulated processes in the world.
The question of BSE and AIDS has arisen because of the use of blood-derived products in the manufacturing of vaccines. For example, serum from calves is a component of the cell culture medium which is used to grow certain vaccine viruses. However, vaccine makers only use certified products from BSE-free countries.
There are also strict rules covering the use of protein components (such as human albumin) which is derived from blood plasma. These proteins are sometimes used to stabilise and preserve live vaccines. Plasma products are rigorously tested for diseases such as HIV-AIDS and hepatitis.
In addition, the vaccine production process includes procedures to kill viruses which might somehow have gone undetected.
The bottom line is that any risk of blood-borne infections is as close to zero as possible. The risk of not having the vaccines which are recommended for you by your doctor and health authorities is much higher.
