By LAU­RAN NEER­GAARD | AS­SO­CI­AT­ED PRESS

(AP) — Pfiz­er is en­rolling healthy adults to test a re­for­mu­lat­ed COVID-19 vac­cine that match­es the huge­ly con­ta­gious omi­cron vari­ant, to see how it com­pares with the orig­i­nal shots.

Pfiz­er and its part­ner BioN­Tech an­nounced the study on Tues­day.

COVID-19 vac­cine-mak­ers have been up­dat­ing their shots to bet­ter match omi­cron in case glob­al health au­thor­i­ties de­cide the change is need­ed.

Omi­cron is more like­ly than pre­vi­ous vari­ants to cause in­fec­tion even in peo­ple who’ve been vac­ci­nat­ed, but it’s not yet clear that a change to the vac­cine recipe will be or­dered. Among the is­sues reg­u­la­tors are weigh­ing: Some of the first places to face an omi­cron surge al­ready are see­ing the mu­tant wane — and there’s no way to know if the next vari­ant that aris­es will re­sem­ble omi­cron or be to­tal­ly dif­fer­ent.

The orig­i­nal vac­cines still of­fer good pro­tec­tion against se­vere ill­ness and death. Stud­ies in the U.S. and else­where have made clear that adding a boost­er dose strength­ens that pro­tec­tion and im­proves the chances of avoid­ing even a milder in­fec­tion.

An­oth­er wrin­kle in de­cid­ing whether vac­cines need an up­date: A new U.S. re­port Tues­day echoes da­ta from Britain and South Africa that omi­cron in­fec­tions cause less se­vere ill­ness — at least in part be­cause so many peo­ple have some pro­tec­tion from vac­ci­na­tion or pri­or in­fec­tion. Dur­ing the omi­cron surge, 13% of hos­pi­tal­ized COVID-19 pa­tients end­ed up in in­ten­sive care, com­pared with about 18% dur­ing two ear­li­er waves, ac­cord­ing to the Cen­ters for Dis­ease Con­trol and Pre­ven­tion.

Still, “we rec­og­nize the need to be pre­pared in the event this pro­tec­tion wanes over time and to po­ten­tial­ly help ad­dress omi­cron and new vari­ants in the fu­ture,” Kathrin Jansen, Pfiz­er’s vac­cine re­search chief, said in a state­ment.

The new U.S. study will in­clude up to 1,420 vol­un­teers ages 18 to 55 to test the up­dat­ed omi­cron-based shots for use as a boost­er or for pri­ma­ry vac­ci­na­tions. Re­searchers will ex­am­ine the tweaked vac­cine’s safe­ty and how it revs up the im­mune sys­tem in com­par­i­son to the orig­i­nal shots.

Full study re­sults will take many months as vol­un­teers re­ceive mul­ti­ple vac­cine dos­es — and as re­searchers mea­sure how long virus-fight­ing an­ti­bod­ies re­main at high lev­els af­ter an omi­cron-adapt­ed dose ver­sus the reg­u­lar boost­er.

Pfiz­er’s CEO told CN­BC ear­li­er this month that the com­pa­ny could have some omi­cron-matched dos­es ready as ear­ly as March. But do­ing what the com­pa­ny calls “at-risk” man­u­fac­tur­ing doesn’t mean those dos­es will be rolled out to the pub­lic. Pfiz­er and oth­er vac­cine mak­ers al­so have brewed and test­ed ex­per­i­men­tal dos­es to match pre­vi­ous vari­ants, changes that ul­ti­mate­ly weren’t need­ed but of­fered valu­able prac­tice at tweak­ing the recipe.

For the new study, one group of about 600 vol­un­teers who re­ceived two dos­es of the cur­rent Pfiz­er vac­cine three to six months ago will re­ceive ei­ther one or two omi­cron-based shots as boost­ers. An­oth­er 600 who have al­ready got­ten three reg­u­lar dos­es of the Pfiz­er vac­cine will be giv­en a fourth dose of ei­ther the reg­u­lar vac­cine or the omi­cron-matched ver­sion.

The study al­so will en­rol some un­vac­ci­nat­ed vol­un­teers who will re­ceive three dos­es of the omi­cron-based vac­cine.

Pfiz­er plans to pro­duce 4 bil­lion vac­cine dos­es in 2022 and said Tues­day the amount isn’t ex­pect­ed to change if an omi­cron-adapt­ed ver­sion is need­ed.

___

As­so­ci­at­ed Press writer Mike Sto­bbe con­tributed to this re­port.