By LAU­RA UN­GAR, As­so­ci­at­ed Press

LOUISVILLE, Ky. (AP) — Cadell Walk­er rushed to get her 9-year-old daugh­ter Solome vac­ci­nat­ed against COVID-19 — not just to pro­tect her, but to help stop the coro­n­avirus from spread­ing and spawn­ing even more dan­ger­ous vari­ants.

“Love thy neigh­bor is some­thing that we re­al­ly do be­lieve, and we want to be good com­mu­ni­ty mem­bers and want to 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 re­al­ly beat COVID is for all of us col­lec­tive­ly to work to­geth­er for the greater good.”

Sci­en­tists agree. Each in­fec­tion — whether in an adult in Yemen or a kid in Ken­tucky — gives the virus an­oth­er op­por­tu­ni­ty to mu­tate. Pro­tect­ing a new, large chunk of the pop­u­la­tion any­where in the world lim­its those op­por­tu­ni­ties.

That ef­fort got a lift with 28 mil­lion U.S. kids 5 to 11 years old now el­i­gi­ble for child-sized dos­es of the Pfiz­er-BioN­Tech vac­cine. Moves else­where, like Aus­tria’s re­cent de­ci­sion to re­quire all adults to be vac­ci­nat­ed and even the U.S. au­tho­riz­ing boost­er shots for all adults on Fri­day, help by fur­ther re­duc­ing the chances of new in­fec­tion.

Vac­ci­nat­ing kids al­so means re­duc­ing silent spread, since most have no or mild symp­toms when they con­tract the virus. When the virus spreads un­seen, sci­en­tists say, it al­so goes un­abat­ed. And as more peo­ple con­tract it, the odds of new vari­ants rise.

David O’Con­nor, a vi­rol­o­gy ex­pert at the Uni­ver­si­ty of Wis­con­sin-Madi­son, likens in­fec­tions to “lot­tery tick­ets that we’re giv­ing the virus.” The jack­pot? A vari­ant even more dan­ger­ous than the con­ta­gious delta cur­rent­ly cir­cu­lat­ing.

“The few­er peo­ple who are in­fect­ed, the less lot­tery tick­ets it has and the bet­ter off we’re all go­ing to be in terms of gen­er­at­ing the vari­ants,” he said, adding that vari­ants are even more like­ly to emerge in peo­ple with weak­ened im­mune sys­tems who har­bor the virus for a long time.

Re­searchers dis­agree on how much kids have in­flu­enced the course of the pan­dem­ic. Ear­ly re­search sug­gest­ed they didn’t con­tribute much to vi­ral spread. But some ex­perts say chil­dren played a sig­nif­i­cant role this year spread­ing con­ta­gious vari­ants such as al­pha and delta.

Get­ting kids vac­ci­nat­ed could make a re­al dif­fer­ence go­ing for­ward, ac­cord­ing to es­ti­mates by the COVID-19 Sce­nario Mod­el­ing Hub, a col­lec­tion of uni­ver­si­ty and med­ical re­search or­ga­ni­za­tions that con­sol­i­dates mod­els of how the pan­dem­ic may un­fold. The hub’s lat­est es­ti­mates show that for this No­vem­ber through March 12, 2022, vac­ci­nat­ing 5- to 11-year-olds would avert about 430,000 COVID cas­es in the over­all U.S. pop­u­la­tion if no new vari­ant arose. If a vari­ant 50% more trans­mis­si­ble than delta showed up in late fall, 860,000 cas­es would be avert­ed, “a big im­pact,” said project co-leader Ka­tri­ona Shea, of Penn­syl­va­nia State Uni­ver­si­ty.

Delta re­mains dom­i­nant for now, ac­count­ing for more than 99% of an­a­lyzed coro­n­avirus spec­i­mens in the Unit­ed States. Sci­en­tists aren’t sure ex­act­ly why. Dr. Stu­art Camp­bell Ray, an in­fec­tious dis­ease ex­pert at Johns Hop­kins Uni­ver­si­ty, said it may be in­trin­si­cal­ly more in­fec­tious, or it may be evad­ing at least in part the pro­tec­tion peo­ple get from vac­cines or hav­ing been in­fect­ed be­fore.

“It’s prob­a­bly a com­bi­na­tion of those things,” he said. “But there’s al­so very good and grow­ing ev­i­dence that delta is sim­ply more fit, mean­ing that it’s able to grow to high­er lev­els faster than oth­er vari­ants that are stud­ied. So when peo­ple get delta, they be­come in­fec­tious soon­er.”

Ray said delta is “a big fam­i­ly” of virus­es, and the world is now swim­ming in a sort of “delta soup.”

“We have many lin­eages of delta that are cir­cu­lat­ing in many places with no clear win­ners,” Ray said, adding that it’s hard to know from ge­net­ic fea­tures which might have an edge, or which non-delta vari­ants might de­throne delta.

“I of­ten say it’s like see­ing a car parked on the side of the road with rac­ing slicks and rac­ing stripes and an air­foil on the back and a big en­gine,” Ray said. “You know it looks like it could be a re­al con­tender, but un­til you see it on the track with oth­er cars, you don’t know if it’s go­ing to win.”

An­oth­er big un­known: Dan­ger­ous vari­ants may still arise in large­ly-un­vac­ci­nat­ed parts of the world and make their way to Amer­i­ca even as U.S. chil­dren join the ranks of the vac­ci­nat­ed.

Walk­er, the Louisville mom, said she and her hus­band can’t do any­thing about dis­tant threats, but could sign their daugh­ter up for vac­ci­na­tion at Jef­fer­son Coun­ty Pub­lic Schools sites on a re­cent week­end. Solome is adopt­ed from Ethiopia and is prone to pneu­mo­nia fol­low­ing res­pi­ra­to­ry ail­ments af­ter be­ing ex­posed to tu­ber­cu­lo­sis as a ba­by.

She said she wants to keep oth­er kids safe be­cause “it’s not good to get sick.”

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.

“Won­der Woman,” Walk­er said. “Per­fect.”

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The As­so­ci­at­ed Press Health and Sci­ence De­part­ment re­ceives sup­port from the Howard Hugh­es Med­ical In­sti­tute’s De­part­ment of Sci­ence Ed­u­ca­tion. The AP is sole­ly re­spon­si­ble for all con­tent.