Several reports have been written about the pandemic 2009 influenza A(H1N1) (A[H1N1]). However, little information is available on the emergence of the later strain, new virus A(H1N1) (An[H1N1]) in the winter of 2010 to 2011.1 Unexpectedly, during the European winter of that period the usual seasonal viruses were replaced by the An(H1N1) virus, and in Spain, 447 patients with severe infection were admitted to the ICU. Although the presenting features of An(H1N1) influenza were quite similar to those described for patients in the ICU with A(H1N1),2-4 some differences should be pointed out. The patients with An(H1N1) were somewhat older (49.7 ± 14.3 years vs 44.7 ± 14.9 years); similarly, the frequency of increased disease severity (APACHE [Acute Physiology and Chronic Health Evaluation] II score 16.4 ± 7.4 vs 13.9 ± 7.2) and multiorgan dysfunction (Sequential Organ Failure Assessment score 6.3 ± 3.8 vs 5.5 ± 3.5) were higher (P < .001) in patients with An(H1N1) than those observed previously in patients with A(H1N1).5 The frequency of comorbidities was similar in both periods, but there was an increase in the number of patients with hematologic disease (11.1% vs 5.3%, P < .001) and HIV infection (4.1% vs 2.1%, P = .03).1,4 Viral pneumonia was the leading cause of hospitalization in both periods. However, a small but significant increase in the need for invasive mechanical ventilation in patients during the seasonal outbreak (69% vs 61.5%, P < .01) was observed.5 The implementation of early (< 2 days) antiviral therapy was associated with a better survival rate.5 Although all patients received antiviral treatment, in the seasonal outbreak, a 1-day delay (5 days instead of 4 days) in the antiviral administration was observed. This apparent treatment delay could be associated with a corresponding difference in the time from symptoms onset to hospital (4.9 days vs 4.3 days, P < .01) or ICU admission (2.3 days vs 1.8 days, P < .01).5 All of these variables must be considered to explain the higher mortality rate observed in patients undergoing invasive mechanical ventilation during the seasonal outbreak of An(H1N1) (42.6%) compared with patients with A(H1N1) (34.2%, P < .001).5 APACHE II score (OR = 1.1; 95% CI, 1.06-1.12), invasive mechanical ventilation (OR = 8.3; 95% CI, 4.32-15.91), hematologic disease (OR = 3.0; 95% CI, 1.66-5.49), HIV infection (OR = 3.9; 95% CI, 1.38-11.51), and antiviral therapy (OR = 0.45; 95% CI, 0.28-0.73) were variables independently associated with mortality. Finally, only 6.2% of patients admitted to the ICU during the seasonal outbreak were vaccinated, and they seemed to have a more favorable outcome with shorter ICU stay (3 days) and fewer days under invasive mechanical ventilation (3 days).