(CNN) The day Candace and Terry Ayers got their second Covid-19 vaccination in early March was a day of hope and excitement for the entire family.
"I took my parents to get that second jab, and we were all so excited," said their son, Marc Ayers. "We are a family that believes in science. We believe in masks, and we believe in vaccines. We were ready to get back to normal."
But his mother, Candace Ayers, died nearly six months later following a July trip with her husband to Mississippi. Her death certificate says she died of Covid-19.
Her obituary, in the local newspaper, the State Journal Register, in Springfield, Illinois, read in part:
"Candace Cay (Kruger) Ayers, 66, of Springfield, passed away on September 3, 2021, at St. John's Hospital in Springfield, IL. She was preceded in death by more than 4,531,799 others infected with Covid-19. She was vaccinated but was infected by others who chose not to be. The cost was her life."
The tally represents the total global coronavirus death toll.
Marc Ayers believes his mother was infected when she visited Mississippi, where vaccination rates remain among the lowest in the nation. Only 42% of Mississippi's population was fully vaccinated by mid-September, according to the state's health department.
"This all could have been avoided," Ayers said. "This could have been prevented by a few acts of kindness. They were in a state that had one of the lowest vaccination rates in the country. Getting a vaccine and wearing a mask for others ... had this been done, she would be here today."
Because Candace had an underlying condition, her family was hesitant for her to leave town.
"My mother had severe rheumatoid arthritis. We were always the most concerned about her getting it because she was immunocompromised," Ayers said. "We were wrestling with whether they should have traveled.
"But things were looking so good, and with them being fully vaccinated, we just didn't have any thoughts of them going to Mississippi. The Delta variant was just hitting the radar. Breakthrough cases were rare at that point. Our worst nightmare came true."
Breakthrough cases occur when someone tests positive for Covid-19 at least 14 days after they have been fully vaccinated, according to the US Centers for Disease Control and Prevention. Such infections can cause disease with symptoms, and some people can have no symptoms at all. Research has shown that if people become infected after vaccination, typically they get a milder case.
Between early April and mid-July -- as the Delta variant was gaining dominance -- fully vaccinated people represented 8% of all Covid-19 cases, 8% of hospitalizations and 9% of deaths, according to a CDC study published this month.
And Candace Ayers was especially vulnerable because she was older and had an underlying health condition. About 70% of breakthrough cases resulting in hospitalization were among adults 65 and older and about 87% of breakthrough cases resulting in death were among adults 65 and older, according to the CDC data.
The Ayers family is having a tough time processing Candace's death and wanted to try to inspire others to get a vaccine and wear a mask, Marc Ayers said. Sharing daily worldwide Covid-19 death numbers in her obituary aimed to make people take pause, he said.
"This was to illustrate that this isn't just an issue contained to the US, but it has a global impact," Ayers said. "My mom was a fighter. She kept fighting and fighting and fighting. We wanted to send a point."
The family has gotten positive and negative feedback to the obituary, he said.
"It's been really wonderful to hear from friends and strangers regarding the obituary. Because of our story," Ayers said, "people have told us they are getting vaccinated.
"Of course, there are negative comments as well, but the majority has been positive."
Correction: An earlier version of this story misstated the name of the US Centers for Disease Control and Prevention. It also mischaracterized breakthrough infections.
CNN's Deidre McPhillips and Aya Elamroussi contributed to this report.