Since the introduction of the first high-rate cooling/warming vitrification technologies, liquid nitrogen mediated disease transfer was always a concern of embryologists and authorities. Unfortunately, up till today, there is not a single closed (“safe”) vitrification method that can compete with the open systems for cryopreservation of human oocytes. On the other hand, out of an estimated two million transfers performed after open vitrification, not a single infection was reported. Accordingly, in most countries, relevant professional organizations and authorities permit, or at least tolerate the use of open systems. In parallel, new measures were suggested to decrease the probability of cross-contamination, including the separate storage of factory-derived liquid nitrogen to be used for cooling, then hermetical sealing of the cooled samples in container straws before transferring them into the common storage container.

The COVID-19 pandemic has created a new challenge for assisted reproduction. Publications, conferences and webinars have extensively discussed various aspects. Recently, an excellent review has been published in Human Reproduction, providing a comprehensive and entirely rational picture of the situation, and with useful advice for handling the problem (Alteri, A., Pisaturo, V., Somigliana, E., Vigano, P.: Cryopreservation in Reproductive Medicine during the COVID-19 Pandemic: Rethinking Policies and European Safety Regulations. Human Reproduction, in press, free full access paper).

Immediately after publication, Dr Lodovico Parmegiani called my attention that one important issue is not discussed in this review, and seems to be forgotten by other authors, too. While previous agents in concern (hepatitis B virus, or HIV) were not airborne, and factory-derived LN2 could be regarded as - more or less - harmless for IVF, COVID-19 may contaminate LN2 at any phase of production, transportation or even handling in the laboratory before using it for cooling with open vitrification devices.

In a Letter to the Editor we called the attention of readers of Human Reproduction to this issue. The letter has been accepted and published (Parmegiani, L., Vajta, G.: Letter: COVID-19 in Liquid Nitrogen: a Potential Danger Still Disregarded. Human Reproduction, in press, free full access paper).

As the letter is accessible to everybody, I summarize only the most important message here: the fact that liquid nitrogen and nitrogen vapour may be contaminated at any step, from manufacturing to final use including transport, storage, distribution and preparation for cryopreservation. Accordingly, the risk in the COVID pandemic is not just related to contaminated patients, operators, cells and tissues, but the liquid nitrogen itself, and strategies to put in place to prevent infections are required.

Please let me use this opportunity to introduce you my friend, Dr Lodovico Parmegiani, my respected friend, one of the brightest embryology experts in Europe. Dr Parmegiani is the Scientific Director of the Reproductive Medicine Center and the Nextclinics International Group, Bologna, Italy, and advisor for many biotech companies. He is founder of the Nterilizer Isrl company, Bologna, Italy, a commercial venture focused on sterilization of liquid nitrogen and nitrogen vapour to be used for cell, tissue, sperm, oocyte and embryo cryopreservation. Dr Parmegiani has more than 60 peer-reviewed publications referred now more than 1,300 times in the scientific literature.

We have a very fruitful collaboration with Dr Parmegiani. We were co-authors in 5 publications, a sixth one, an opinion paper is under consideration now – and we have ambitious plans to expand our joint efforts in technical issues including the safe use of liquid nitrogen in our laboratories.