Regards serology, in our study with only 22% of patients developing a titer to H1N1 generally accepted as being protective, although no patient developed protective titers to either H3N2 or influenza B. The low response could be due to the fact that these are previously unvaccinated, and therefore would need a second dose of vaccine, on the contrary, as evidenced by our data, a single dose of vaccine would be effective anyway to make the priming of CD4+ T lymphocytes in the majority of vaccine subjects. Here, CD4 is linked to influenza.