In­ves­ti­ga­tors at As­traZeneca have or­dered a halt to dos­ing their close­ly-watched Covid-19 vac­cine in or­der to probe a po­ten­tial­ly se­vere ad­verse event — re­port­ed­ly in­volv­ing in­flam­ma­tion of the spinal cord — suf­fered by one of the tri­al par­tic­i­pants.

In a state­ment out Tues­day evening, a spokesman for the phar­ma gi­ant told End­points News that the study had been put on hold to in­ves­ti­gate an ill­ness. Lat­er Tues­day, they sent a re­vised state­ment, which not­ed that the halt is vol­un­tary, not or­dered by reg­u­la­tors. It reads:

As part of the on­go­ing ran­domised, con­trolled glob­al tri­als of the Ox­ford coro­n­avirus vac­cine, our stan­dard re­view process was trig­gered and we vol­un­tar­i­ly paused vac­ci­na­tion to al­low re­view of safe­ty da­ta by an in­de­pen­dent com­mit­tee. This is a rou­tine ac­tion which has to hap­pen when­ev­er there is a po­ten­tial­ly un­ex­plained ill­ness in one of the tri­als, while it is in­ves­ti­gat­ed, en­sur­ing we main­tain the in­tegri­ty of the tri­als. In large tri­als ill­ness­es will hap­pen by chance but must be in­de­pen­dent­ly re­viewed to check this care­ful­ly. We are work­ing to ex­pe­dite the re­view of the sin­gle event to min­imise any po­ten­tial im­pact on the tri­al time­line. We are com­mit­ted to the safe­ty of our par­tic­i­pants and the high­est stan­dards of con­duct in our tri­als.

The spokesman did not say what ill­ness was in­volved, but the New York Times re­port­ed that the halt was trig­gered by a case in the UK of trans­verse myelitis, an in­flam­ma­tion of the spinal cord that can in­ter­rupt mes­sages that spinal cord nerves trans­mit. Ac­cord­ing to Johns Hop­kins, “it is char­ac­ter­ized by symp­toms and signs of neu­ro­log­ic dys­func­tion in mo­tor and sen­so­ry tracts on both sides of the spinal cord.”

The con­di­tion can be trig­gered by a va­ri­ety of things, in­clud­ing vac­ci­na­tions.

As­traZeneca’s shares slid 6% af­ter the bell on Tues­day, a sharp drop for a Big Phar­ma of that size. Shares of Mod­er­na and BioN­Tech, the two mR­NA lead­ers in Phase III, each jumped 5%.

This is the first such pause in the fren­zied race to get a Covid-19 vac­cine to the goal line. And the in­ter­rup­tion on a Covid-19 leader like this trig­gered head­lines world­wide. As­traZeneca, like the rest of the lead­ing de­vel­op­ers work­ing on a pan­dem­ic vac­cine, has been bar­rel­ing ahead in­to late-stage piv­otal work on a jab for the coro­n­avirus that has dis­rupt­ed the world. But at every quick step, ex­ecs at the multi­na­tion­al have al­so re­peat­ed­ly as­sured all in­volved that they will not hes­i­tate to slow things down if war­rant­ed.

The next big ques­tion is how long As­traZeneca’s vac­cine could be on pause and whether there could be a spillover in­volv­ing oth­er vac­cine mak­ers.

An­drew Berens at SVB Leerink put it this way, siz­ing up the im­pact if it is trans­verse myelitis:

AZN’s vac­cine study may be post­poned by weeks to months, as the safe­ty data­base is scru­ti­nized and tri­al pro­to­cols re­vised. Fur­ther, this AE could have the po­ten­tial to slow down vac­cine de­vel­op­ment more broad­ly. Trans­verse myelitis has not been de­fin­i­tive­ly linked to any com­mer­cial vac­cines, but it has been shown to be re­lat­ed to nat­ur­al virus in­fec­tion, and a few cas­es of trans­verse myelitis were de­scribed af­ter ad­min­is­tra­tion of the MMR, vari­cel­la, and he­pati­tis B vac­cines (the mech­a­nis­tic ev­i­dence was de­ter­mined to be weak per the In­sti­tute of Med­i­cine, cur­rent­ly the Na­tion­al Acad­e­my of Med­i­cine).

Safe­ty is­sues — par­tic­u­lar­ly when they could be tied to a se­ri­ous ad­verse event — loom par­tic­u­lar­ly large here. Any sug­ges­tion of a safe­ty prob­lem could raise con­cerns for all in­volved, pos­ing added prob­lems in the event they pro­voke pub­lic re­sis­tance to a shot. And there are po­lit­i­cal im­pli­ca­tions as well. As Pres­i­dent Trump has promised a vac­cine by year’s end, or even soon­er, the top vac­cines have a shot at a snap OK. Safe­ty is­sues would put a vac­cine fur­ther be­hind in the line.

Jef­feries’ Michael Yee was quick to pick up on that as­pect, writ­ing:

While we see this event as more of a short- to medi­um-term top­ic for de­bate, we do be­lieve these vac­cines will like­ly end up be­ing dif­fer­en­ti­at­ed on ef­fi­ca­cy and safe­ty in their Phase II­Is, which could dri­ve opin­ions on which is “best” and even­tu­al mar­ket up­take.

At our lat­est count, we in­clude the As­traZeneca vac­cine in 3rd place among 29 com­pa­nies in or near the clin­ic, right be­hind the mR­NA lead­ers at Pfiz­er/BioN­Tech and Mod­er­na. They’ve been work­ing with $1.2 bil­lion in pub­lic fi­nanc­ing for this work, with the Phase III get­ting un­der­way in Ju­ly. In­ves­ti­ga­tors plan to re­cruit 30,000 pa­tients in the US and 50,000 world­wide as they look for a broad pa­tient group to test safe­ty and ef­fi­ca­cy.

For a look at all End­points News coro­n­avirus sto­ries, check out our spe­cial news chan­nel.

Genmab $GMAB has opted to ax one of its antibody-drug conjugates after watching it flop in the clinic.

The Danish biotech reported Tuesday that it decided to kill their program for enapotamab vedotin after the data gathered from expansion cohorts failed to measure up. According to the company:

While enapotamab vedotin has shown some evidence of clinical activity, this was not optimized by different dose schedules and/or predictive biomarkers. Accordingly, the data from the expansion cohorts did not meet Genmab’s stringent criteria for proof-of-concept.

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Although the Rgeneron drug is not the first antibody treatment authorized by the FDA, the news comes as a significant milestone for a company and a treatment scientists have watched closely since the outbreak began.

For much of the pharmaceutical industry, the pandemic presented an opportunity: to prove their value to the world and turn public opinion around on a business much of the country had come to disdain.

That theory — that helping pull the country from a pandemic could neutralize years of anger over high drug prices — was put to its biggest test this month, as three different drugmakers announced data from their Covid-19 vaccines, offering the first major evidence that industry-built inoculations could turn the tide of the outbreak in the US.