Cadell Walker rushed to get her 9-year-old daughter Solome immunized against COVID-19, not only to protect her, but also to help prevent the coronavirus from spreading and spawning even more dangerous variants.

“We really believe in love thy neighbor, and we want to be good community members and model that thinking for our daughter,” said the 40-year-old Louisville mom, who recently took Solome to a local middle school for her shot. “The only way to truly defeat COVID is for all of us to band together for the greater good.”

Scientists are in agreement. Each infection, whether in an adult in Yemen or a child in Kentucky, provides the virus with another chance to mutate. Protecting a new, large segment of the global population limits those opportunities.

This effort has been boosted by the fact that 28 million US children aged 5 to 11 are now eligible for child-sized doses of the Pfizer-BioNTech vaccine. Moves elsewhere, such as Austria’s recent decision to require all adults to be vaccinated, and the United States’ approval of booster shots for all adults on Friday, help by lowering the likelihood of new infection.

Vaccinating children also means reducing silent spread, because most people who contract the virus have no or mild symptoms. Scientists believe that when the virus spreads unnoticed, it continues unabated. And as more people contract it, the likelihood of new variants increases.

Infections, according to David O’Connor, a virology expert at the University of Wisconsin-Madison, are like “lottery tickets that we’re giving the virus.” The grand prize? A variant that is even more dangerous than the currently circulating contagious delta.

“The fewer people who are infected, the fewer lottery tickets it has, and the better off we’ll all be in terms of generating the variants,” he said, adding that variants are more likely to emerge in people with weakened immune systems who have been infected for a long time. Researchers disagree on the extent to which children influenced the course of the pandemic. Early research indicated that they did not play a significant role in viral spread. However, some experts believe that children played a significant role in spreading contagious variants such as alpha and delta this year.

According to the COVID-19 Scenario Modeling Hub, a collection of university and medical research organizations that consolidates models of how the pandemic may unfold, getting children vaccinated could make a significant difference in the future. According to the hub’s most recent estimates, vaccinating 5- to 11-year-olds would prevent approximately 430,000 COVID cases in the overall U.S. population if no new variant emerged from November to March 12, 2022. If a variant that is 50% more transmissible than delta appears in late fall, 860,000 cases could be avoided, according to project co-leader Katriona Shea of Pennsylvania State University.

Delta remains dominant for the time being, accounting for more than 99 percent of coronavirus specimens analyzed in the United States. Scientists are baffled as to why this is happening. Dr. Stuart Campbell Ray, an infectious disease expert at Johns Hopkins University, believes it may be more infectious by nature, or it may be evading at least some of the protection provided by vaccines or previous infection.

According to Ray, delta is a “big family” of viruses, and the world is currently swimming in a “delta soup.”

“We have many lineages of delta that are circulating in many places with no clear winners,” Ray said, adding that it’s difficult to predict which non-delta variants will dethrone delta based on genetic features.

Another unknown: Dangerous variants may still emerge in largely unvaccinated parts of the world and make their way to America, even as more American children become vaccinated.

Walker, the Louisville mother, said she and her husband couldn’t do anything about distant threats, but they could sign their daughter up for vaccinations at Jefferson County Public Schools locations on a recent weekend. Solome was adopted from Ethiopia and is prone to pneumonia as a result of respiratory problems caused by tuberculosis as a baby. As a nurse leaned in to give Solome her shot, Walker held her daughter’s hand, then praised her for picking out a post-jab sticker appropriate for a brave kid who just did her part to help curb a pandemic.