Error copying one vector to onother in C++

I want to copy one vector to another. I have two similar types of codes. The 1st one ("check_1.C") works but the second one did not work ("check_2.C").

Could you please suggest and explain.

1st code (working):

double Refm[10] = {4  , 9 , 18 , 32 , 52 , 80 , 118 , 172 , 206 , 300};
double p_low[9] = {0.88, 0.72, 0.89, 0.84, 0.75, 0.71, 0.79, 0.69, 0.66};
double p_high[9] = {0.14, 0.19, 0.16, 0.24, 0.21, 0.27, 0.22, 0.29, 0.25};
const int centrality_bin = 9;

void check_1()
{
    vector<vector<double> > eff_cen;
    eff_cen.resize(Refm[9]+1);

    vector<vector<double> > eff;

    for(int jj = 0; jj < centrality_bin; jj++)
    {
        eff_cen[jj].push_back(p_low[jj]);
        eff_cen[jj].push_back(p_high[jj]);

        cout<<"eff_cen[" << jj << "]  = ";
        for(size_t kk=0; kk<eff_cen[jj].size(); kk++) cout<<eff_cen[jj].at(kk)<<" ";

        eff.push_back(eff_cen[jj]); // I CAN COPY CORRECTLY

        for(size_t nn=0; nn<eff[jj].size(); nn++) cout<<eff[jj].at(nn)<<" ";
        cout << endl;
    }
}

2nd code (not working):

double Refm[10] = {4  , 9 , 18 , 32 , 52 , 80 , 118 , 172 , 206 , 300};
double p_low[9] = {0.88, 0.72, 0.89, 0.84, 0.75, 0.71, 0.79, 0.69, 0.66};
double p_high[9] = {0.14, 0.19, 0.16, 0.24, 0.21, 0.27, 0.22, 0.29, 0.25};


void check_2()
{
    vector<vector<double> > eff_cen;
    eff_cen.resize(Refm[9]+1);

    vector<vector<double> > eff;
    //eff.resize(Refm[9]+1);

    for(int z = 0; z < 9; z++) {
        for(int jj = Refm[z]+1; jj <= Refm[z+1]; jj++)
        {
            eff_cen[jj].push_back(p_low[z]);
            eff_cen[jj].push_back(p_high[z]);

            cout<<"eff_cen[" << jj << "]  = ";
            for(size_t kk=0; kk<eff_cen[jj].size(); kk++) cout<<eff_cen[jj].at(kk)<<" ";              
            eff.push_back(eff_cen[jj]); // COPY DOES NOT WORK
            for(size_t nn=0; nn<eff[jj].size(); nn++) cout<<eff[jj].at(nn)<<" ";              cout << endl;
        }
    }
}