drop like ninepins

To succumb to a particular problem, often an illness. This phrase is typically only used when more than one person has been adversely affected. Ninepins is a game that is similar to bowling. Primarily heard in UK. Now that the flu is going through our school, people are dropping like ninepins. The illness seems to be really contagious—everyone I know has been dropping like ninepins. Once one of your kids gets sick, you know it's only a matter of time until they're all dropping like ninepins.

ˌgo down, ˌdrop, etc. like ˈninepins

(informal)
1 (of large numbers of people) become ill/sick, be killed or die at the same time: In last year’s flu epidemic both children and teachers at this school were going down like ninepins. ♢ As the enemy advanced, men and horses went down like ninepins.
2 (of businesses, etc.) fail, go out of business, etc: Small businesses are going down like ninepins at the moment.

In the game of ninepins, you roll a ball towards a group of nine wooden objects (= skittles) in order to knock down as many of them as possible.