Sci­en­tists at North­eastern Uni­ver­sity in Boston hypo­thet­i­cally released smallpox in London, New York, Paris, and other major cities, and then sim­u­lated it being car­ried by trav­ellers to other countries.

They pub­lished their find­ings in Sci­en­tific Reports, saying they believe a delib­erate smallpox infec­tion would spread to up to four coun­tries before doc­tors diag­nosed it.

These maps show what they pre­dict would be the effect of a smallpox release in London, with the top map showing how far the dis­ease would have spread before author­i­ties realise.

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