"Our thoughts and sympathies go out to the parents, family, and others who are impacted by this tragedy," the county's public health officer, Dr. Geoffrey Leung, said in a statement. "This loss reminds us that this virus does not discriminate between the young and old."
Officials said the child, who was from southwest Riverside County and was less than 1 year old, had been taken to a local hospital after becoming ill. The infant's name and city of residence were not disclosed.
The child's death "strengthens our commitment to end this pandemic before the loss of another young life," Leung said. "It shows the importance of using the tools available to protect those around us, particularly the most innocent, from the harm the virus can cause."
More than 5,600 COVID-19-related deaths have occurred in Riverside County since early 2020, according to Riverside University Health System. The overwhelming majority of those deaths involved people who were over 30 years old. However, "there have been a handful of teens and young adults who have died from the virus - some with underlying health issues," a news release said.
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Whether the infant who died this week had any underlying health issues was unknown, officials said.
"It is devastating to learn about the passing of this infant life. Our hearts and thoughts go out to the family," said county Board of Supervisors Chairman Jeff Hewitt. "We have a long road ahead of us as we navigate this pandemic and it's the loss of life that reminds us about the challenges we face."
Previously, the youngest COVID-19-related death in Riverside County was a 4-year-old child who died in August, according to health officials.
Infants under age 1 might be at higher risk of severe illness with COVID-19 than older children, Riverside University Health System said. This is likely due to their immature immune systems and smaller airways, which make them more likely to develop breathing issues with respiratory virus infections.