To the Editor: Pregnant women and their offspring are at increased risk for influenza-related complications.¹ During the 2009 influenza A(H1N1) pandemic, the estimated rate of admission for complications in pregnant women was 4 times higher than in the general population, accounting for 13% of all A(H1N1) deaths.² Childhood deaths associated with influenza A(H1N1) were most frequent in infants younger than 6 months.³ Influenza vaccination appears to be both safe and effective in pregnant women and elicits an antibody response comparable with age-matched, nonpregnant control participants,⁴ which could result in the passive transfer of sufficient antibody to protect their infants for the duration of the influenza season.^5,6

It is unclear whether the ability to respond to vaccines is restored by antiretroviral therapy. We evaluated the influenza-specific immune responses elicited by a virosomal vaccine in HIV-infected children on long-term successful highly active antiretroviral therapy (HAART). This was an observational, prospective, open-label study enrolling 24 HIV-infected, HAART-treated (85 months' mean exposure), vaccine-naive children (median age=11.9 years) and 14 age- and gender-matched healthy controls. Mean CD4 T-cell counts (>900 cells/microL) and percentages (>37%) were comparable. The HIV RNA level was or=4-fold Ab titer raise in >40% of patients) and seroprotection (Ab titer>or=1:40 in >70% of patients) was achieved at 1 month in both groups; however, fewer HIV-infected children fulfilled these criteria. The A/H3N2- and A/H1N1-specific Ab geometric mean titers were lower in HIV-infected children compared with healthy controls at 1 and 6 months; interestingly, a boost in vaccine-specific IgG3 T helper 1 type Ab was seen in healthy controls alone. Finally, vaccine specific-IFNgamma- and IL-2-producing T lymphocytes were reduced at both time points in HIV-infected children compared with healthy controls. One injection of virosomal-adjuvanted influenza vaccine stimulates good immune responses, although the humoral and cellular immune responses are reduced in HIV-infected children compared to healthy children. This indicates that immunologic function impairments may persist upon HIV infection even if HIV-positive viremia is suppressed and immune recovery seems to be achieved.

Measles is one of the most contagious diseases known to man. Despite the existence of a safe and effective live attenuated vaccine, measles can appear in vaccinated individuals. Paradoxically, breakthrough cases increase as vaccination coverage in the general population rises. In measles endemic areas, breakthrough cases represent less than 10% of total infections, while in areas with high vaccination coverage these are over 10% of the total. Two different vaccination failures have been described: primary vaccination failure, which consists in the complete absence of humoral response and occurs in around 5% of vaccinated individuals; and secondary vaccination failure is due to waning immunity or incomplete immunity and occurs in 2–10% of vaccinees. Vaccination failures are generally associated with lower viral loads and milder disease (modified measles) since vaccination limits the risk of complicated disease. Vaccination failure seems to occur between six and twenty-six years after the last vaccine dose administration. This review summarizes the literature about clinical, serological, epidemiological, and molecular characteristics of measles breakthrough cases and their contribution to virus transmission. In view of the measles elimination goal, the assessment of the potential decline in antibody protection and the targeted implementation of catch-up vaccination are essential.