The cu­ri­ous im­munol­o­gy be­hind the UK's sur­prise As­traZeneca dos­ing plan

As ex­pect­ed, UK reg­u­la­tors au­tho­rized As­traZeneca’s Covid-19 vac­cine on Wednes­day. What was less ex­pect­ed were the in­struc­tions au­thor­i­ties gave when OK­ing it: Peo­ple could re­ceive the two dos­es of the vac­cine as many as 12 weeks apart — three times as long as the pe­ri­od stud­ied in the com­pa­ny’s clin­i­cal tri­als.

The de­ci­sion set off a de­bate. Some sci­en­tists and epi­demi­ol­o­gists said it could put more jabs in more arms faster, with new ev­i­dence sug­gest­ing that the vac­cine be­gins to of­fer pro­tec­tion af­ter just a sin­gle dose. Oth­ers point­ed out there was no di­rect ev­i­dence giv­ing the vac­cine in this way would work, adding more ques­tions to a vac­cine that has al­ready spent two months mired in con­tro­ver­sy.

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