Clare Hoang, 31, smiles as she and her 3-year-old son Gryphon lead his Ukiah-area preschool class in singing "Do You Know the Colors of the Rainbow."
But the smile cannot hide the sadness in her face.
Gryphon's identical twin brother, Phoenix, died last month from a rare and virulent disease, meningococcemia, which infects the bloodstream and attacks organs. It is caused by the same group of bacteria that can cause meningitis, which affects the brain and spinal column.
The bacterial infection struck swiftly, stopping his heart about 12 hours after the onset of flu-like symptoms, she said. He was revived but then taken off life support two days later when tests showed he was brain dead.
At times, "I feel like I'm going to cry my heart through my mouth," Hoang said.
She's emerged from the depths of grief to tell her story in hopes it will save other children.
Hoang has begun campaigning to vaccinate young children for infections caused by a group of bacteria called Neisseria meningitidis, the type that killed her son.
"No child should die from something that is preventable," she said.
Hoang plans to speak before a federal panel of experts responsible for establishing vaccination routines -- the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices -- in June.
She joins the debate over the benefits and pitfalls of trying to vaccinate against meningococcal disease.
Some health officials say the benefits are dubious because current vaccines for infants are effective against only about half of the types of bacteria that cause meningococcal disease. Parents say they want whatever protection that is available for their children.
The CDC vaccine panel has recommended that Neisseria meningitidis vaccine be regularly given only to children over age 11 unless they travel to countries where the disease is prevalent or they have a compromised immune system.
The vaccine also is highly recommended for young adults heading off to college or the military, where close quarters makes transmission more likely. It usually is spread through saliva or respiratory droplets.
Dr. Amanda Cohn, who specializes in meningitis at the CDC, said she could not speak for the panel but reasons for not recommending meningococcal vaccines at young ages could be related to the rarity of the disease and because the vaccine is less effective at younger ages.
Phoenix's death was the first fatality in Mendocino County since 2008, when another infant about 2 years old succumbed to the infection. Sonoma County's last fatality was a 27-year-old in 2010.
Nationwide, about 800 cases a year of Neisseria meningitidis are reported and 10 to 15 percent are fatal, she said.
The disease has been in decline nationally. In the 1990s, there were closer to 3,000 cases reported each year. It's also on the decline in California, where 112 cases were reported in 2011 compared with 215 in 2002, according to the state health department. Fourteen deaths were reported in California last year.
"It's very rare in this country," Cohn said.
But even one death is too many, Hoang and other vaccination advocates say. Survivors often are left with debilitating conditions, including amputated limbs, deafness and blindness, they say.
Hoang is working to create an advocacy foundation and has joined an Internet petition drive seeking to change vaccine policies on meningococcal vaccines for infants.