Choice of Study Populations for Vaccines

Correlates of postnatal human cytomegalovirus transmission in term babies in the first year

Postnatal human cytomegalovirus (HCMV) infection in newborns is well characterized for preterm infants but less so for term infants. We sought to analyze the rates and routes of HCMV transmission in full-term infants during the first year of life. A cohort of 120 HCMV seropositive mothers and their 122 newborns were tested after delivery for HCMV-DNA shedding in different bodily fluids. Postnatal HCMV infection was defined as the detection of >2.5 × 102 HCMV-DNA copies/mL in infants' saliva swabs. Maternal neutralizing antibody serum titer, HCMV-specific T-cell response, and HCMV glycoprotein B immunoglobulin G on breastmilk were analyzed. HCMV shedding was detected in 67 of 120 mothers (55.8%), and 20 of 122 infants (16.4%) developed HCMV infection within the first 3 months of life. Six additional infants were infected during the first year, for a postnatal infection rate of 21.3%. Viral shedding was more frequent in breastmilk than saliva, urine, and vaginal secretions, and the mothers of infected infants showed higher levels of HCMV-DNA in milk. No association was found between the antibody levels in serum or milk and maternal viral shedding, whereas a slightly lower frequency of HCMV-specific CD4+ T-cells with long-term memory phenotype was observed in women with HCM-DNA-positive milk. About one out of five infants develop HCMV infection within the first year of life. Breastmilk appears the major route of transmission of the infection, maternal saliva has a minor role whereas the role of vaginal secretions is negligible.

Seroprevalence of Cytomegalovirus and Associated Factors Among Preconception Women: A Cross-Sectional Nationwide Study in China

Background: Cytomegalovirus seroconversion during pregnancy is common and has a substantial risk of congenital infection with longterm sequale. Screening during pregnancy or vaccination have not been shown to be effective for eliminating congenital infections. Preconception screening policy has not been evaluated adequately in a large scale. This nationwide study aimed to investigate epidemiological features of cytomegalovirus seropositivity and its geographic variation among Chinese women planning a pregnancy to gather epidemiological evidence as an essential for developing novel prevention strategies. Method: This cross-sectional sero-epidemiological survey enrolled women intending to become pregnant within 6 months in mainland China during 2010-2012. The primary outcomes in this study were cytomegalovirus Immunoglobulin G and M seropositivity. Secondary outcomes were the associations between Immunoglobulin G and Immunoglobulin M, with socio-demographic characteristics, including age, occupation, education level, place of residence, and ethnicity. The overall seropositivity and regional disparity was analyzed on the individual and regional level, respectively. Results: This study included data from 1,564,649 women from 31 provinces in mainland China. Among participants, 38.6% (n = 603,511) were cytomegalovirus immunoglobulin G+, 0.4% (n = 6,747) were immunoglobulin M+, and 0.2% (n = 2,879) were immunoglobulin M+ and immunoglobulin G+. On individual level, participant's age, ethnicity, and residing region were significantly associated with IgG+, IgM+, and IgM+IgG+ (P < 0.001), while occupation, education level, and place of residence were not statistically significant (P > 0.05). On regional level, cytomegalovirus immunoglobulin G and immunoglobulin M seropositivity was highest in the eastern region (49.5 and 0.5%, respectively), and lowest in the western region (26.9 and 0.4%, respectively). This geographic variation was also noted at the provincial level, characterized by higher provincial immunoglobulin M+ and immunoglobulin G+ rates associated with higher immunoglobulin G seropositivity. In the subgroup analysis of immunoglobulin G seropositivity, areas of higher immunoglobulin G positivity had a higher rate of immunoglobulin M+, indicating an expected increased risk of reinfection and primary infection. Conclusions: A substantial proportion of women (>60%) were susceptible to cytomegalovirus in preconception period in China, and immunoglobulin G seropositivity was seen at a low-medium level with substantial geographic variation. Integration of cytomegalovirus antibody testing in preconception screening program based on regional immunoglobulin G seropositivity, should be considered to promote strategies directed toward preventing sero-conversion during pregnancy to reduce the risk of this congenital infection.

Is it time to adopt routine cytomegalovirus screening in pregnancy? No!

Congenital cytomegalovirus is caused by maternal primary or nonprimary infection during pregnancy and is a major preventable cause of neurodisability. The proposed strategies to reduce congenital cytomegalovirus include primary prevention with maternal hygiene measures and secondary prevention by serologic screening for detecting maternal primary infection. A recent randomized trial found that high-dose valaciclovir treatment resulted in a significant reduction in fetal infection after first-trimester maternal primary infection, leading to calls to start routine serologic screening in pregnancy. Previously, observational studies have found a reduction in fetal infection with after maternal primary cytomegalovirus infection when hyperimmune globulin is administered twice weekly during the first trimester of pregnancy; however, this has not been replicated in randomized trials that have used different regimens. Furthermore, some evidence from a single intervention trial and observational studies do not provide us with the necessary data required for rolling out an appropriate screening program. All screening tests may be associated with harm; in the case of congenital cytomegalovirus, there is the well-recognized potential for increasing terminations of pregnancy without diagnostic confirmation of fetal infection or sequelae. Although valaciclovir and hyperimmune globulin treatments may significantly reduce fetal infection rates, they do not prevent severe cytomegalovirus-related fetal brain damage in all pregnancies. Therefore, it is not clear that the offer of a prenatal intervention will provide sufficient reassurance to screen-positive women. In addition, the effectiveness of a prenatal screening and treatment strategy is predicated on a high rate of maternal primary infection, which is limited to regions with low cytomegalovirus seroprevalence, such as Western Europe. In some countries, such as the United States, Finland, and Brazil, nonprimary maternal infections are responsible for most congenital cytomegalovirus health burdens, limiting the potential impact of pregnancy screening. In this invited clinical perspective, we reviewed the evidence and outlined the steps needed to be taken before determining whether the benefits of routine screening for cytomegalovirus in pregnancy outweigh the harms. Until we have the necessary evidence, we should follow the current advice of multiple national health authorities and focus on promoting primary prevention through maternal hygiene precautions.

Pathogenesis of human cytomegalovirus in the immunocompromised host

Human cytomegalovirus (HCMV) is a herpesvirus that infects ~60% of adults in developed countries and more than 90% in developing countries. Usually, it is controlled by a vigorous immune response so that infections are asymptomatic or symptoms are mild. However, if the immune system is compromised, HCMV can replicate to high levels and cause serious end organ disease. Substantial progress is being made in understanding the natural history and pathogenesis of HCMV infection and disease in the immunocompromised host. Serial measures of viral load defined the dynamics of HCMV replication and are now used routinely to allow intervention with antiviral drugs in individual patients. They are also used as pharmacodynamic read-outs to evaluate prototype vaccines that may protect against HCMV replication and to define immune correlates of this protection. This novel information is informing the design of randomized controlled trials of new antiviral drugs and vaccines currently under evaluation. In this Review, we discuss immune responses to HCMV and countermeasures deployed by the virus, the establishment of latency and reactivation from it, exogenous reinfection with additional strains, pathogenesis, development of end organ disease, indirect effects of infection, immune correlates of control of replication, current treatment strategies and the evaluation of novel vaccine candidates.