  LitCovid (https://www.ncbi.nlm.nih.gov/research/coronavirus/), first launched
in February 2020, is a first-of-its-kind literature hub for tracking up-to-date
published research on COVID-19. The number of articles in LitCovid has
increased from 55,000 to ~300,000 over the past two and half years, with a
consistent growth rate of ~10,000 articles per month. In addition to the rapid
literature growth, the COVID-19 pandemic has evolved dramatically. For
instance, the Omicron variant has now accounted for over 98% of new infections
in the U.S. In response to the continuing evolution of the COVID-19 pandemic,
this article describes significant updates to LitCovid over the last two years.
First, we introduced the Long Covid collection consisting of the articles on
COVID-19 survivors experiencing ongoing multisystemic symptoms, including
respiratory issues, cardiovascular disease, cognitive impairment, and profound
fatigue. Second, we provided new annotations on the latest COVID-19 strains and
vaccines mentioned in the literature. Third, we improved several existing
features with more accurate machine learning algorithms for annotating topics
and classifying articles relevant to COVID-19. LitCovid has been widely used
with millions of accesses by users worldwide on various information needs and
continues to play a critical role in collecting, curating, and standardizing
the latest knowledge on the COVID-19 literature.
