"Recognizing the growing interest in preprints, NLM is [...] launching the first phase of the NIH-Preprint-Pilot, which will test the viability of making preprints searchable in PubMed Central (PMC) and, by extension, discoverable in PubMed, starting with COVID-19 preprints reporting NIH-supported research."

Detailed information as well as links can be found in the article of the NLM "The NIH Preprint Pilot: A New Experiment for a New Era".