Long-term persistence of immunity and B-cell memory following Haemophilus influenzae type B conjugate vaccination in early childhood and response to booster

Completion of multidose vaccine series in early childhood: current challenges and opportunities

PURPOSE OF REVIEW

Completion of all doses in multidose vaccine series provides optimal protection against preventable infectious diseases. In this review, we describe clinical and public health implications of multidose vaccine series noncompletion, including current challenges to ensuring children receive all recommended vaccinations. We then highlight actionable steps toward achieving early childhood immunization goals.

RECENT FINDINGS

Although coverage levels are high for most early childhood vaccinations, rates of completion are lower for vaccinations that require multiple doses. Recent research has shown that lower family socioeconomic status, a lack of health insurance coverage, having multiple children in the household, and moving across state lines are associated with children failing to complete multidose vaccine series. These findings provide contextual evidence to support that practical challenges to accessing immunization services are impediments to completion of multidose series. Strategies, including reminder/recall, use of centralized immunization information systems, and clinician prompts, have been shown to increase immunization rates. Re-investing in these effective interventions and modernizing the public health infrastructure can facilitate multidose vaccine series completion.

SUMMARY

Completion of multidose vaccine series is a challenge for immunization service delivery. Increased efforts are needed to address remaining barriers and improve vaccination coverage in the United States.

A comprehensive method for the phenotypical and functional characterization of recalled human memory B and T cells specific to vaccine antigens

Current methodologies for assessing vaccine effectiveness and longevity primarily center on measuring vaccine-induced neutralizing antibodies in serum or plasma. However, these methods overlook additional parameters such as the presence of memory B cells, even as antibody levels wane, and the pivotal role played by memory T cells in shaping antigen-specific memory B cell responses. Several studies have employed a combination of polyclonal activators, such as CpG and R848, along with various cytokines to provoke the recall of memory B cells from peripheral blood mononuclear cells (PBMCs) into antibody-secreting cells (ASCs). Other studies have examined the use of live attenuated viruses to stimulate antigen-specific memory T cells within PBMCs into effector T cells that produce Th1/Th2 cytokines. However, these studies have not fully elucidated the distinct effects of these polyclonal activators on individual subsets, nor have they evaluated whether the vaccine antigen alone is sufficient to trigger the recall of memory T cells. Thus, in this study, we directly compared the capacity of two B cell polyclonal activators to induce the transition of existing vaccine-specific memory cells present in peripheral blood samples into ASCs. Simultaneously, we also assessed the transition of existing memory T cells into effector subsets in response to vaccine antigens. Our findings demonstrate that both polyclonal activator combinations, CpG with IL-6 and IL-15, as well as R848 with IL-2, effectively induce the terminal differentiation of memory B cells into ASCs. Notably, CpG treatment preferentially expanded naïve and non-class-switched B cells, while R848 expanded class-switched memory cells, plasmablasts, and plasma cells. Consequently, R848 treatment led to a greater overall production of total and antigen-specific IgG immunoglobulins. Additionally, the exposure of isolated PBMCs to vaccine antigens alone proved sufficient for recalling the rare antigen-specific memory T cells into effector subsets, predominantly consisting of IFN-γ-producing CD4 T cells and TNF-β-producing CD8 T cells. This study not only establishes a rationale for the selection of methods to expand and detect antigen-specific lymphocyte subsets but also presents a means to quantify vaccine effectiveness by correlating serum antibody levels with preexisting memory cells within peripheral blood samples.

Harnessing the Potential of Multiomics Studies for Precision Medicine in Infectious Disease

The field of infectious diseases currently takes a reactive approach and treats infections as they present in patients. Although certain populations are known to be at greater risk of developing infection (eg, immunocompromised), we lack a systems approach to define the true risk of future infection for a patient. Guided by impressive gains in "omics" technologies, future strategies to infectious diseases should take a precision approach to infection through identification of patients at intermediate and high-risk of infection and deploy targeted preventative measures (ie, prophylaxis). The advances of high-throughput immune profiling by multiomics approaches (ie, transcriptomics, epigenomics, metabolomics, proteomics) hold the promise to identify patients at increased risk of infection and enable risk-stratifying approaches to be applied in the clinic. Integration of patient-specific data using machine learning improves the effectiveness of prediction, providing the necessary technologies needed to propel the field of infectious diseases medicine into the era of personalized medicine.

Protection Against Invasive Infections in Children Caused by Encapsulated Bacteria

The encapsulated bacteria Streptococcus pneumoniae, Neisseria meningitis, Haemophilus influenzae, and Streptococcus agalactiae (Group B Streptococcus) have been responsible for the majority of severe infections in children for decades, specifically bacteremia and meningitis. Isolates which cause invasive disease are usually surrounded by a polysaccharide capsule, which is a major virulence factor and the key antigen in protective protein-polysaccharide conjugate vaccines. Protection against these bacteria is largely mediated via polysaccharide-specific antibody and complement, although the contribution of these and other components, and the precise mechanisms, vary between species and include opsonophagocytosis and complement-dependent bacteriolysis. Further studies are required to more precisely elucidate mechanisms of protection against non-type b H. influenzae and Group B Streptococcus.

Maternal immunization

Pregnant women, neonates, and infants are at higher risk for severe infections due to vaccine-preventable diseases. Very young infants rarely respond well to vaccination due to poor immunogenicity and interference from maternal antibody. Maternal immunization protects the mother and fetus from disease and protects the infant through transplacental antibody transfer through the first 6 months of life. Currently, immunizations routinely recommended during pregnancy include inactivated influenza, tetanus toxoid, and acellular pertussis vaccines. Promising maternal vaccine candidates in development include a group B streptococcus vaccine and a respiratory syncytial virus vaccine. Birth Defects Research 109:379-386, 2017. © 2017 Wiley Periodicals, Inc.

A review of Haemophilus influenzae disease in Europe from 2000-2014: challenges, successes and the contribution of hexavalent combination vaccines

INTRODUCTION

The development of diphtheria-tetanus-acellular pertussis-Haemophilus influenzae type b (Hib) conjugate vaccine combinations culminated with hexavalent vaccines, the largest, most complex vaccine combinations in the immunization calendar. Hexavalent vaccines are used widely in Europe and are co-administered with multiple other recommended vaccines. Hib immunogenicity may reduce when combined with acellular pertussis antigens, or in some co-administrations. We reviewed the epidemiology of H. influenzae disease in Europe aiming to evaluate the current level of Hib control and indirectly assess the effectiveness against Hib of GSK's hexavalent vaccine in 10 countries where it is/has been used almost exclusively. Areas covered: We reviewed surveillance data from the European Union Invasive Bacterial Infections Surveillance Network and the European Surveillance System database from 1999-2014 and extracted case and incidence/notification rates (per 100,000 population) of invasive H. influenzae disease. We included age and serotype/strains distribution among countries in the European Union/European Economic Area region that reported to the European Centre for Disease Prevention and Control surveillance system. Expert commentary: The impact of Hib vaccination in Europe is sustained, testifying to continued effectiveness against invasive Hib disease after the implementation of hexavalent vaccines into immunization programs, which, since 2006, has been almost exclusively GSK´s hexavalent DTPa-HBV-IPV/Hib vaccine.

Differential B-cell memory around the 11-month booster in children vaccinated with a 10- or 13-valent pneumococcal conjugate vaccine

Infants vaccinated with the 10- or 13-valent pneumococcal conjugate vaccine at 2, 3, 4, and 11 months had similar serotype-specific immunoglobulin G levels and plasma cell frequencies against 4 shared serotypes around these boosters, but higher memory B-cell frequencies in the PCV13 group.

Background. Both the 10- and 13-valent pneumococcal conjugate vaccines (PCV10 and PCV13) induce immunological memory against Streptococcus pneumoniae infections caused by vaccine serotypes. In addition to comparing serum antibody levels, we investigated frequencies of serotype-specific plasma cells (PCs) and memory B-cells (Bmems) as potential predictors of long-term immunity around the booster vaccination at 11 months of age.

Methods. Infants were immunized with PCV10 or PCV13 at 2, 3, 4, and 11 months of age. Blood was collected before the 11-month booster or 7–9 days afterward. Serotype-specific immunoglobulin G (IgG) levels were determined in serum samples by multiplex immunoassay. Circulating specific PCs and Bmems against shared serotypes 1, 6B, 7F, and 19F and against PCV13 serotypes 6A and 19A were measured in peripheral blood mononuclear cells by enzyme-linked immunospot assay.

Results. No major differences in IgG levels and PC frequencies between groups were found for the 4 shared serotypes. Notably, PCV13 vaccination resulted in higher frequencies of Bmems than PCV10 vaccination, both before and after the booster dose, for all 4 shared serotypes except for serotype 1 postbooster. For PCV13-specific serotypes 6A and 19A, the IgG levels and frequencies of PCs and Bmems were higher in the PCV13 group, pre- and postbooster, except for PC frequencies prebooster.

Conclusions. Both PCVs are immunogenic and induce measurable IgG, PC, and Bmem booster responses at 11 months. Compared to PCV10, vaccination with PCV13 was associated with overall similar IgG levels and PC frequencies but with higher Bmem frequencies before and after the 11-month booster. The clinical implications of these results need further follow-up.

Clinical Trials Registration. NTR3069.

Effect of antenatal parasitic infections on anti-vaccine IgG levels in children: a prospective birth cohort study in Kenya

Background

Parasitic infections are prevalent among pregnant women in sub-Saharan Africa. We investigated whether prenatal exposure to malaria and/or helminths affects the pattern of infant immune responses to standard vaccinations against Haemophilus influenzae (Hib), diphtheria (DT), hepatitis B (Hep B) and tetanus toxoid (TT).

Methods and Findings

450 Kenyan women were tested for malaria, schistosomiasis, lymphatic filariasis (LF), and intestinal helminths during pregnancy. After three standard vaccinations at 6, 10 and 14 weeks, their newborns were followed biannually to age 36 months and tested for absolute levels of IgG against Hib, DT, Hep B, and TT at each time point. Newborns’ cord blood (CB) lymphocyte responses to malaria blood-stage antigens, soluble Schistosoma haematobium worm antigen (SWAP), and filaria antigen (BMA) were also assessed. Three immunophenotype categories were compared: i) tolerant (those having Plasmodium-, Schistosoma-, or Wuchereria-infected mothers but lacking respective Th1/Th2-type recall responses at birth to malaria antigens, SWAP, or BMA); ii) sensitized (those with infected/uninfected mothers and detectable Th1/Th2-type CB recall response to respective parasite antigen); or iii) unexposed (no evidence of maternal infection or CB recall response).

Overall, 78.9% of mothers were infected with LF (44.7%), schistosomiasis (32.4%), malaria (27.6%) or hookworm (33.8%). Antenatal maternal malaria, LF, and hookworm were independently associated with significantly lower Hib-specific IgG. Presence of multiple maternal infections was associated with lower infant IgG levels against Hib and DT antigens post-vaccination. Post-vaccination IgG levels were also significantly associated with immunophenotype: malaria-tolerized infants had reduced response to DT, whereas filaria-tolerized infants showed reduced response to Hib.

Conclusions

There is an impaired ability to develop IgG antibody responses to key protective antigens of Hib and diphtheria in infants of mothers infected with malaria and/or helminths during pregnancy. These findings highlight the importance of control and prevention of parasitic infections among pregnant women.

Parasitic infections are prevalent among pregnant women in sub-Saharan Africa. Prenatal exposure to parasitic infections can generate several potential effects on fetal immune responses and affect functional antibody generation during subsequent vaccination. There is a paucity of data on the detrimental effects of chronic parasitic infections during pregnancy on the response to vaccine from birth to childhood. This paper highlights the overwhelming presence of helminth infection and malaria in pregnant women in rural Kenya. The study shows that the presence of single and multiple antenatal parasitic infections is associated with impaired infant IgG levels against Haemophilus influenzae (Hib) and diphtheria (DT) antigens post-vaccination from birth to 30 months of age. This study found that the response to DT was reduced in malaria-tolerized infants, and the response to Hib was impaired in filarial-tolerized infants; by contrast, the Schistosoma-tolerized group showed no effect. Deworming campaigns must be directed towards pregnant mothers, infants, and young children to improve response to vaccination.

Maternal immunization

Maternal immunization has the potential to protect the pregnant woman, fetus, and infant from vaccine-preventable diseases. Maternal immunoglobulin G is actively transported across the placenta, providing passive immunity to the neonate and infant prior to the infant's ability to respond to vaccines. Currently inactivated influenza, tetanus toxoid, and acellular pertussis vaccines are recommended during pregnancy. Several other vaccines have been studied in pregnancy and found to be safe and immunogenic and to provide antibody to infants. These include pneumococcus, group B Streptococcus, Haemophilus influenzae type b, and meningococcus vaccines. Other vaccines in development for potential maternal immunization include respiratory syncytial virus, herpes simplex virus, and cytomegalovirus vaccines.