Emily Scarratt, Katy McLean, Amy Wilson-Hardy and Amy Cockayne all also claimed scores, with a penalty try rounding off another rout as Simon Middleton’s side topped Pool B, which also included Italy and Spain.
The USA scrambled a try bonus point in defeat however, thanks to scores from Kate Zackary, Cheta Emba, Naya Tapper and Kristen Thomas.
But England were not to be denied safe passage to the last four with a powerful win in Dublin, Middleton’s side joining New Zealand in reaching the semi-finals.
“We did a really good job on all three teams, or maybe two-and-a-half jobs as the USA were outstanding,” said Middleton.
“Everybody would’ve preferred us to finish the game better than we did but the bottom line is we were absolutely outstanding in the first half.
“We were clear in thought, our execution was fantastic and we had the job done by half-time.
“It wasn’t an easy pool at all. We’ve dealt really well with the group and we’re really pleased that we’ve achieved our objective which was to get out of it and get to a semi-final. We’re looking forward to that.”
Scarratt kicked off England’s comfortable win, reaching McLean’s neat grubber first to dot down.
The 2014 world champions then flexed their tight-game muscles with a fine rolling lineout maul that was brought down illegally by the USA’s Katy Augustyn.
Augustyn was sin-binned and England awarded a penalty try, handing Middleton’s side early control.
England profited from another driven maul when Packer rose last from the pile of bodies to claim her side’s third score.
And when England and Packer capped another driven maul with their fourth score, the game looked over as a contest as early as the 26th minute, with England leading 28-0.
Flanker Zackary hit back for the USA though, with the converted try handing the Americans a foothold on the scoreboard.
McLean restored the England supremacy with their fifth try however, to leave Middleton’s side coasting at 33-7 to the good at the break.
Wilson-Hardy capped a flowing move for the sixth score straight after the restart, before Cockayne finished the seventh try after just 48 minutes.
The USA refused to go quietly however, with full-back Emba sneaking home for a score, before England sent on a raft of replacements.
Tapper took advantage of the disarray to step through traffic for a smart score for the USA, before Thomas claimed the bonus point try on the stroke of full-time.
New Zealand crushed Canada 48-5 in Dublin to finish top of Pool A.
The Black Ferns, four-time World Cup winners, recorded a third successive bonus-point victory, scoring eight tries to inflict a first defeat of the tournament on their opponents.
Prop Aldora Itunu led the way with a hat-trick, while there were also tries for Selica Winiata, Stacey Waaka, Kelly Brazier, Fiao’o Fa’amausili and Renee Wickliffe, with Brazier adding one conversion and scrum-half Kendra Cocksedge booting three.