sys = {S'[t] == (0.02* S[t] - ((0.02*S[t]^2)/10^+6)- ((0.02*S[t]*II[t])/10^+6) - S[t]*10^-4*V[t]), II'[t] == 10^-4*S[t]*V[t] - 0.01*II[t] - 0.0082*II[t], V'[t] == 100*10^-4*II[t] - 50*V[t], P'[t] ==   0.0082*II[t] + P[t] - (1510416.6667*(P[t]^2)/(744047.619^2 + P[t]^2))- 1.3*10^-7*EE[t]*P[t] + (24 + 7.2*(1 - 0.9997))*Cp[t] - 0.5*10^-6*P[t]*A[t],  CC'[t] == ((1510416.6667*P[t]^2)/(744047.619^2 + P[t]^2)) - 1.01*CC[t], EE'[t] == 1.36*10^4 - 0.0412*EE[t] + (((0.2988*10^8)*(Cp[t] + Ca[t]))/(2.02*10^7 + P[t])) - 1.3*10^-7*EE[t]*P[t] + (24 + 7.2*0.9997)*Cp[t] - 1.3*10^-7*L[t]*E[t] + 24*Ca[t] + 7.2*Ca[t] + 2*24*Ce[t] -
 2*1.3*10^-7*EE[t]^2 + 7.2*Ce[t], A'[t] == 1.36*10^4 - 0.0412*A[t] - 0.5*10^-6*P[t]*A[t] + 10*L[t],  L'[t] == 0.5*10^-6*P[t]*A[t] - 10*L[t] - 1.3*10^-7*L[t]*EE[t] + 24*Ca[t], Cp'[t] == 1.3*10^-7*EE[t]*P[t] - (24 + 7.2)*Cp[t], Ca'[t] == 1.3*10^-7*L[t]*EE[t] - (24 + 7.2)*Ca[t], Ce'[t] == 1.3*10^-7*EE[t]^2 - (24 + 7.2)*Ce[t], S[0] == 10^+6,  II[0] == 0, V[0] == 10^+2, P[0] == 0, CC[0] == 0, EE[0] == 0, A[0] == 0, L[0] == 0, Cp[0] == 0, Ca[0] == 0, Ce[0] == 0};

s = NDSolve[sys, {S[t], II[t], V[t], P[t], CC[t], EE[t], A[t], L[t], Cp[t], Ca[t], Ce[t]}, {t, 0, 400}, Method -> {"ExplicitRungeKutta","DifferenceOrder" -> 4}]

Plot[Evaluate[({P[t]} /. s) ],{t,0,400}]