By MATTHEW PER­RONE and LAU­RAN NEER­GAARD-As­so­ci­at­ed Press 

WASH­ING­TON (AP) — U.S. reg­u­la­tors on Thurs­day strict­ly lim­it­ed who can re­ceive John­son & John­son’s COVID-19 vac­cine due to the on­go­ing risk of rare but se­ri­ous blood clots. 

The Food and Drug Ad­min­is­tra­tion said the shot should on­ly be giv­en to adults who can­not re­ceive a dif­fer­ent vac­cine or specif­i­cal­ly re­quest J&J’s vac­cine. U.S. au­thor­i­ties for months have rec­om­mend­ed that Amer­i­cans get Pfiz­er or Mod­er­na shots in­stead of J&J’s vac­cine. 

FDA’s vac­cine chief Dr. Pe­ter Marks said the agency de­cid­ed to re­strict the vac­cine af­ter tak­ing an­oth­er look at the da­ta on the risks of life-threat­en­ing blood clots and con­clud­ing that they are lim­it­ed to J&J’s vac­cine. 

“If there’s an al­ter­na­tive that ap­pears to be equal­ly ef­fec­tive in pre­vent­ing se­vere out­comes from COVID-19, we’d rather see peo­ple opt­ing for that,” Marks said. “But we’ve been care­ful to say that-- com­pared to no vac­cine-- this is still a bet­ter op­tion.” 

The prob­lem oc­curs in the first two weeks af­ter vac­ci­na­tion, he added: “So if you had the vac­cine six months ago you can sleep sound­ly tonight know­ing this isn’t an is­sue.” 

The FDA au­tho­rized J&J’s shot in Feb­ru­ary last year for adults 18 and up. 

The vac­cine was ini­tial­ly con­sid­ered an im­por­tant tool in fight­ing the pan­dem­ic be­cause it re­quired on­ly one shot. But the sin­gle-dose op­tion proved less ef­fec­tive than two dos­es of the Pfiz­er and Mod­er­na vac­cines. 

In De­cem­ber, the Cen­ters for Dis­ease Con­trol and Pre­ven­tion rec­om­mend­ed Mod­er­na and Pfiz­er shots over J&J’s be­cause of its safe­ty is­sues. 

As of mid-March, fed­er­al sci­en­tists had iden­ti­fied 60 cas­es of the side ef­fect, in­clud­ing nine that were fa­tal. That amounts to 3.23 blood clot cas­es per 1 mil­lion J&J shots. The prob­lem is more com­mon in women un­der 50, where the death rate was rough­ly 1 per mil­lion shots, ac­cord­ing to Marks. 

Marks said the FDA spent ex­tra time an­a­lyz­ing the prob­lem to be sure it wasn’t con­nect­ed to a sep­a­rate is­sue, such as women tak­ing birth con­trol med­ica­tions that raise their risk of clot­ting. 

The J&J vac­cine will car­ry a stark­er warn­ing about po­ten­tial “long-term and de­bil­i­tat­ing health con­se­quences” of the side ef­fect. 

Un­der the new FDA in­struc­tions, J&J’s vac­cine could still be giv­en to peo­ple who had a se­vere al­ler­gic re­ac­tion to one of the oth­er vac­cines and can’t re­ceive an ad­di­tion­al dose. J&J’s shot could al­so be an op­tion for peo­ple who refuse to re­ceive the mR­NA vac­cines from Pfiz­er and Mod­er­na, and there­fore would oth­er­wise re­main un­vac­ci­nat­ed, the agency said. 

A J&J spokesman said in an emailed state­ment: “Da­ta con­tin­ue to sup­port a fa­vor­able ben­e­fit-risk pro­file for the John­son & John­son COVID-19 vac­cine in adults, when com­pared with no vac­cine.” 

The clot­ting prob­lems first came up last spring, with the J&J shot in the U.S. and with a sim­i­lar vac­cine made by As­traZeneca that is used in oth­er coun­tries. At that time, U.S. reg­u­la­tors de­cid­ed the ben­e­fits of J&J’s one-and-done vac­cine out­weighed what was con­sid­ered a very rare ri sk — as long as re­cip­i­ents were warned. 

COVID-19 caus­es dead­ly blood clots, too. But the vac­cine-linked kind is dif­fer­ent, be­lieved to form be­cause of a rogue im­mune re­ac­tion to the J&J and As­traZeneca vac­cines be­cause of how they’re made. Clots form in un­usu­al places, such as veins that drain blood from the brain, and in pa­tients who al­so de­vel­op ab­nor­mal­ly low lev­els of the platelets that form clots. Symp­toms of the un­usu­al clots in­clude se­vere headaches a week or two af­ter the J&J vac­ci­na­tion — not right away — as well as ab­dom­i­nal pain and nau­sea. 

The New Brunswick, New Jer­sey-based com­pa­ny an­nounced last month that it didn’t ex­pect a prof­it from the vac­cine this year and was sus­pend­ing sales pro­jec­tions. 

The roll­out of the com­pa­ny’s vac­cine was hurt by a se­ries of trou­bles, in­clud­ing man­u­fac­tur­ing prob­lems at a Bal­ti­more fac­to­ry that forced J&J to im­port mil­lions of dos­es from over­seas. 

Ad­di­tion­al­ly, reg­u­la­tors added warn­ings about the blood clots and a rare neu­ro­log­i­cal re­ac­tion called Guil­lain-Bar­ré syn­drome. 

Pfiz­er and Mod­er­na have pro­vid­ed the vast ma­jor­i­ty of COVID-19 vac­cines in the U.S. More than 200 mil­lion Amer­i­cans have been ful­ly vac­ci­nat­ed with the com­pa­nies’ two-dose shots while less than 17 mil­lion Amer­i­cans got the J&J shot. 

This ver­sion cor­rects the rate of blood clots re­port­ed with J&J’s vac­cine. It is 3.23 cas­es per 1 mil­lion vac­ci­na­tions.