Pegasys is a form of pegulated interferonPegylated IFN given weekly has been shown to have equal efficacy as IFN given trice weekly. The most recent guideline (Nordic MPD Study Group) recommendation is: ” Recommendation: IFN-α is theoretically superior for treating PV as it is effective in controlling proliferation of all cell lineages and there is no risk of leukemogenesis. Molecular remissions can be
acheived with IFN. It is most likely to be tolerated in patients below 60 years for whom it is
recommended. Pegylated forms of IFN seem equally effective as conventional IFN.
Grade B recommendation, evidence level III.

In summary, recent data suggest that pegylated INF alfa-2a (Pegasys; Hoffman-La Roche, Inc, Nutley, NJ) is likely to be as effective as IFN.
Barosi G, Lupo L, Rosti V. Management of myeloproliferative neoplasms: from academic guidelines to clinical practice.Curr Hematol Malig Rep. 2012 Mar;7(1):50-6.

McMullin MF, Bareford D, Campbell P, et al.: Guidelines for the diagnosis, investigation and management of polycythaemia/erythrocytosis. Br J Haematol 130 (2): 174-95, 2005.

Campbell PJ, Green AR: The myeloproliferative disorders. N Engl J Med 355 (23): 2452-66, 2006.
Finazzi G, Barbui T: How I treat patients with polycythemia vera. Blood 109 (12): 5104-11, 2007. 

Kiladjian JJ, Cassinat B, Chevret S, et al.: Pegylated interferon-alfa-2a induces complete hematologic and molecular responses with low toxicity in polycythemia vera. Blood 112 (8): 3065-72, 2008

Cortes, MD, Deborah Thomas, MD, Guillermo Garcia-Manero, MD, Alessandra Ferrajoli, MD, Stefan Faderl, MD, Mary Ann Richie, Miloslav Beran, MD, PhD, DVM, Francis Giles, MD, Srdan Verstovsek, MD, PhD Final Result of a Phase 2 Study PEG-IFN–2b therapy in BCR-ABL-negative myeloproliferative disorders Cancer Volume 110 Issue 9, Pages 2012 – 2018

http://www.sfhem.se/filarkiv/files/vardprogram/NMPDGuidelines2007.pdf

and

http://www.hematology.dk/download.php?137ce10569b47edb9f4347782879fa97

Samuelsson J, Mutschler M, Birgegård G, Gram-Hansen P, Björkholm M, Pahl HL Limited effects on JAK2 mutational status after pegylated interferon alpha-2b therapy in polycythemia vera and essential thrombocythemia. Haematologica. 2006 Sep;91(9):1281-2.

ASCO 2011, 461 High Rates of Molecular Response After Long-Term Follow-up of Patients with Advanced Essential Thrombocythemia (ET) or Polycythemia Vera (PV) Treated with Pegylated Interferon-ALFA-2A (PEG-IFN-α-2A; PEGASYS )