Karin Nielsen is a professor of pediatrics in the Division of Infectious Diseases at the University of California, Los Angeles (UCLA) Children’s Hospital and a member of the UCLA faculty. She is an attending physician for Pediatric Infectious Diseases Division at Mattel Children’s Hospital and co-director of the Care-4-Families human immunodeficiency virus (HIV) clinic at UCLA.

She was born in Rio de Janeiro, where she obtained medical training from the University of Rio de Janeiro and completed a pediatric residency at the Hospital dos Servidores do Estado, also in Rio. She obtained further training at UCLA where she completed clinical and research fellowships in pediatric infectious diseases and obtained a master’s degree in public health with a focus on epidemiology.

Nielsen’s main area of research has been perinatal with a focus on pediatric infections, particularly the prevention of mother to child transmission of HIV and prevention of HIV sexual transmission, as well as treatment of this disease in children, adolescents and adults. She presently leads a study of early treatment of HIV infection in at-risk youth in Los Angeles and New Orleans.

Nielsen has worked extensively in collaborative clinical studies in the United States, Brazil, Sub-Saharan Africa, Europe and Asia focused on Zika virus perinatal infection, as well as other congenital infections, arboviral diseases, tuberculosis in children, HIV prevention and treatment and now severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

In response to the coronavirus disease 2019 (COVID-19) pandemic, Nielsen and her colleagues from UCLA and the Oswaldo Cruz Foundation (Fiocruz) in Brazil developed a study of maternal-infant outcomes following COVID-19 in pregnancy, the COVID-19 Outcomes in Mother-Infant Pairs (COMP) study, which is currently enrolling participants in Los Angeles and Rio de Janeiro. She is also an investigator in the COVI-Pregnancy Registry based in Europe and is presently conducting epidemiological studies of COVID-19-infected youth in Los Angeles and Rio de Janeiro.

Nielsen has authored over 300 publications and mentored 117 health professionals to date from the Americas, Europe, Africa and Asia. She is an elected member of the Society for Pediatric Research, the American Pediatric Society and the International AIDS Society.