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In the light of the recent WMAP results we update the constraints on a classof non standard BBN models with a simultaneous combination of non standardneutrino distributions and extra effective number of neutrinos in the expansionrate. These models can be described in terms of the two parameters DeltaN_nu^tot, constrained by the primordial Helium abundance Y_p measurement, andDelta N_nu^rho, constrained by a combination of CMB and primordial Deuteriumdata. Small deviations from standard BBN are suggested. Different non standardscenarios can be distinguished by a measurement of the difference DeltaN_nu^f_nu=Delta N_nu^tot-Delta N_nu^rho. From the current data we estimateDelta N_nu^f_nu simeq -1.4^{+0.9}_{-1.4}, mildly disfavouring solutions with alow expansion rate, characterized by Delta N_nu^f_nu=0 and negative DeltaN_nu^rho. Active-sterile neutrino mixing could be a viable explanation only forhigh values of Y_p gtrsim 0.24. The existence of large positive neutrinochemical potentials xi_i sim 0.05, implying Delta N_nu^rho simeq 0, would be apossible explanation of the data within the analyzed class of non standard BBNmodels. Interestingly it would also provide a way to evade the cosmologicalbounds for `class A 3+1' four neutrino mixing models. A scenario with adecaying sterile neutrino is also considered.Comment: addendum to hep-ph/0108182 after WMAP results; 10 pages; v3: to  appear on PRD, added discussion on decaying nu_s

Addendum to “Update on neutrino mixing in the early universe”