Twenty-eight people stabbed on a crowded street by a drunken German teenager are receiving protective treatment for the next four weeks after it emerged that one victim was HIV positive, authorities said on Sunday.

A drunken knife-wielding teenager stabbed randomly at people leaving a ceremony to dedicate Berlin’s new central rail station just before midnight on Friday and injured 28 in a 10-minute orgy of violence before he was stopped by security guards.

All but four of the 28 people injured in the attack were released by Sunday. Fifteen of the 28 had critical wounds when taken to a nearby hospital on Friday.

The attack came as a shock to Germany less than two weeks before the World Cup soccer tournament opens, casting a shadow over the fireworks, concert and light show celebrations to open the new station that some 500,000 people watched.

“We’ve started HIV prophylaxis with 28 people,” Charite hospital head doctor Dirk Schuermann told Reuters. “The chances of an HIV infection through a knife wound is three in 1,000. The prophylaxis can reduce the risk by another 80 percent.”