The following opinion is based on the up-todate review of the literature made by Gabor Vajta at the request of the EMBCOL practice committee.
1. Vitrification systems, based on a direct contact between the oocytes and liquid Nitrogen (LN2) during vitrification, are proven to be effective for cryopreservation of human oocytes.
2. Only systems which provide for a storage within a sealed enclosure can be considered completely safe from the point of view of the risk, albeit theoretical, of cross-contamination with blood-born pathogens.
3. Vitrification systems that do not provide a direct contact with LN2 during vitrification stage virtually eliminate the risk of infection transmission, but limited data do not prove conclusively that they are equally effective to open systems in preserving human oocytes functionality.
4. More research and development, as well as experience, is required to create a closed system that would be as effective as an open system while preserving the benefit of preventing cross-contamination.