COVID-​​19 has caused an unprece­dented pub­lic health cri­sis and eco­nomic shock to the global econ­omy. While many coun­tries were affected, regions with an older pop­u­la­tion and weaker pub­lic health inter­ven­tions tended to suf­fer more mor­bid­ity and mor­tal­ity. We devel­oped an open-​​source/​open data age-​​specific and multiple-​​stage susceptible-​​exposed-​​infected-​​recovered-​​hospitalized-​​quarantined-​​dead (SEIR-​​HQD) model Uti­liz­ing the lat­est esti­mates of epi­demi­o­log­i­cal para­me­ters and demo­graphic data, we model the poten­tial effects of var­i­ous inter­ven­tions in four rep­re­sen­ta­tive cities with dif­fer­ent pop­u­la­tion struc­tures — New York, Los Ange­les, Daegu and Nairobi. Our mod­el­ing quan­ti­fies the value of early inter­ven­tions, which avoided an addi­tional 5%, 16%, 37% and 43% of the infec­tions in Daegu, Nairobi, New York and Los Ange­les, respec­tively, com­pared to what has been observed in the four cities. Crit­i­cally, we find that school clo­sures, work­ing from home, and reduc­tion in other mobil­ity were most ben­e­fi­cial for younger pop­u­la­tion (0–19 years old), middle-​​age (20–59 years old) pop­u­la­tion and older pop­u­la­tion (60 years and older), respec­tively across each city. Specif­i­cally, school clo­sure avoided 25%, 18%, 16% and 12% of the infec­tions for the pop­u­la­tion under 20 years old in Daegu, Los Ange­les, New York and Nairobi, respec­tively. A 50% and 80% pop­u­la­tion work­ing from home pol­icy avoids 8% and 15% of the infec­tions. Reduc­tion in mobil­ity was more effec­tive than the work­ing from home strat­egy. Any sin­gle social dis­tanc­ing pol­icy if enacted alone can delay the spread of COVID-​​19 but was unable to totally sup­press the infec­tion. Coor­di­nated pol­icy action can be highly effec­tive. Increas­ing the quar­an­tine rate to 10% of infec­tious cases was more effec­tive than strict social dis­tanc­ing alone in this study, although together they can sup­press 80% of the epi­demic. A com­bi­na­tion of mod­er­ate social dis­tanc­ing and quar­an­tine strate­gies was able to avoid 99% of the infections.