Antibody Levels at 3-Years Follow-Up of a Third Dose of Measles-Mumps-Rubella Vaccine in Young Adults.

Mumps outbreaks and breakthrough infections of measles and rubella have raised concerns about waning of vaccine-induced immunity after two doses of measles-mumps-rubella (MMR) vaccination. In the present follow-up study, serum IgG antibodies against mumps, measles and rubella, as well as the functional neutralizing antibodies against both the mumps vaccine strain and mumps outbreak strains were measured longitudinally in young adults that received a third MMR (MMR3) dose. The mumps-specific IgG and virus neutralizing antibody levels at 3 years after vaccination were still elevated compared to pre-vaccination antibody levels, although the differences were smaller than at earlier timepoints. Interestingly, subjects with low antibody levels to mumps before vaccination benefited the most as they showed the strongest antibody increase after an MMR3 dose. Three years after an MMR3 dose, all subjects had antibody levels to measles and rubella above the internationally agreed antibody cutoff levels for clinical protection. Our data support the recommendation that an MMR3 dose may provide additional protection for those that have become susceptible to mumps virus infection during outbreaks. MMR3 also resulted in an increase in anti-measles and rubella antibody levels that lasted longer than might have been expected.

A Third Dose of Measles-Mumps-Rubella Vaccine to Improve Immunity Against Mumps in Young Adults.

BACKGROUND: Waning of vaccine-induced immunity is considered to play a central role in the reemergence of mumps among vaccinated young adults. The aim of the present study was to investigate antibody responses and safety of a third dose of measles-mumps-rubella vaccine (MMR-3) in 150 young adults. Antibody levels were related to a surrogate of protection based on preoutbreak serum antibody levels in 31 persons with and 715 without serological evidence of mumps. METHODS: Mumps virus-specific immunoglobulin G (IgG) antibody responses and mumps virus-neutralizing antibody responses (based on the focus-reduction neutralizing test) against both the Jeryl Lynn mumps virus vaccine strain (hereafter, the "vaccine strain") and the MuVi/Utrecht.NLD/40.10 outbreak strain (hereafter, the "outbreak strain") were determined, and vaccine safety was evaluated. RESULTS: Four weeks following MMR-3 receipt, levels of IgG, anti-vaccine strain, and anti-outbreak strain antibodies increased by a factor of 1.65, 1.34, and 1.35, respectively. Although antibody levels decreased 1 year later, they were still above the baseline level by a factor of 1.37, 1.15, and 1.27, respectively. Based on the surrogate protective antibody cutoff, significantly more participants were protected against mumps virus infection up to 1 year after vaccination (ie, they had antibody levels above the presumed threshold for herd immunity). CONCLUSIONS: MMR-3 receipt increased antibody levels that may protect against mumps virus infection for longer than previously assumed and is expected to be a good and safe intervention for controlling a mumps outbreak. CLINICAL TRIALS REGISTRATION: 2016-001104-36; NTR5911.

Early Measles Vaccination During an Outbreak in the Netherlands: Short-Term and Long-Term Decreases in Antibody Responses Among Children Vaccinated Before 12 Months of Age.

BACKGROUND: The majority of infants will not be protected by maternal antibodies until their first measles vaccination, between 12 and 15 months of age. This provides incentive to reduce the age at measles vaccination, but immunological consequences are insufficiently understood, and long-term effects are largely unknown. METHODS: A total of 79 infants who received early measles vaccination between 6 and 12 months age and a second dose at 14 months of age were compared to 44 children in a control group who received 1 dose at 14 months of age. Measles virus-specific neutralizing antibody concentrations and avidity were determined up to 4 years of age. RESULTS: Infants who first received measles vaccination before 12 months of age had a long-term decrease in the concentration and avidity of measles virus-specific neutralizing antibodies, compared with infants in the control group. For 11.1% of children with a first dose before 9 months of age, antibody levels at 4 years of age had dropped below the cutoff for clinical protection. CONCLUSIONS: Early measles vaccination provides immediate protection in the majority of infants but yields a long-term decrease in neutralizing antibody responses, compared to vaccination at a later age. Additional vaccination at 14 months of age does not improve this. Over the long term, this may result in an increasing number of children susceptible to measles.

Influenza virus A(H1N1)2009 antibody-dependent cellular cytotoxicity in young children prior to the H1N1 pandemic.

Pre-existing immunity played a significant role in protection during the latest influenza A virus H1N1 pandemic, especially in older age groups. Structural similarities were found between A(H1N1)2009 and older H1N1 virus strains to which humans had already been exposed. Broadly cross-reactive antibodies capable of neutralizing the A(H1N1)2009 virus have been implicated in this immune protection in adults. We investigated the serological profile of a group of young children aged 9 years (n=55), from whom paired blood samples were available, just prior to the pandemic wave (March 2009) and shortly thereafter (March 2010). On the basis of A(H1N1)2009 seroconversion, 27 of the 55 children (49 %) were confirmed to be infected between these two time points. Within the non-infected group of 28 children (51 %), high levels of seasonal antibodies to H1 and H3 HA1 antigens were detected prior to pandemic exposure, reflecting past infection with H1N1 and H3N2, both of which had circulated in The Netherlands prior to the pandemic. In some children, this reactivity coincided with specific antibody reactivity against A(H1N1)2009. While these antibodies were not able to neutralize the A(H1N1)2009 virus, they were able to mediate antibody-dependent cellular cytotoxicity (ADCC) in vitro upon interaction with the A(H1N1)2009 virus. This finding suggests that cross-reactive antibodies could contribute to immune protection in children via ADCC.

Mumps-specific cross-neutralization by MMR vaccine-induced antibodies predicts protection against mumps virus infection.

BACKGROUND: Similar to other recent mumps genotype G outbreaks worldwide, most mumps patients during the recent mumps genotype G outbreaks in the Netherlands had received 2 doses of measles, mumps and rubella (MMR) vaccine during childhood. Here, we investigate the capacity of vaccine-induced antibodies to neutralize wild type mumps virus strains, including mumps virus genotype G. METHODS: In this study, we tested 105 pre-outbreak serum samples from students who had received 2 MMR vaccine doses and who had no mumps virus infection (n=76), symptomatic mumps virus infection (n=10) or asymptomatic mumps virus infection (n=19) during the mumps outbreaks. In all samples, mumps-specific IgG concentrations were measured by multiplex immunoassay and neutralization titers were measured against the Jeryl Lynn vaccine strain and against wild type genotype G and genotype D mumps virus strains. RESULTS: The correlation between mumps-specific IgG concentrations and neutralization titers against Jeryl Lynn was poor, which suggests that IgG concentrations do not adequately represent immunological protection against mumps virus infection by antibody neutralization. Pre-outbreak neutralization titers in infected persons were significantly lower against genotype G than against the vaccine strain. Furthermore, antibody neutralization of wild type mumps virus genotype G and genotype D was significantly reduced in pre-outbreak samples from infected persons as compared with non-infected persons. No statistically significant difference was found for the vaccine strain. The sensitivity/specificity ratio was largest for neutralization of the genotype G strain as compared with the genotype D strain and the vaccine strain. CONCLUSIONS: The reduced neutralization of wild type mumps virus strains in MMR vaccinated persons prior to infection indicates that pre-outbreak mumps virus neutralization is partly strain-specific and that neutralization differs between infected and non-infected persons. Therefore, we recommend the use of wild type mumps virus neutralization assays as preferred tool for surveillance of protection against mumps virus infection.

Development of an IFNγ ELISPOT for the analysis of the human T cell response against mumps virus.

In the last decade, mumps virus (MuV) causes outbreaks in highly vaccinated populations. Sub-optimal T cell immunity may play a role in the susceptibility to mumps in vaccinated individuals. T cell responses to mumps virus have been demonstrated, yet the quality of the MuV-specific T cell response has not been analyzed using single cell immunological techniques. Here we developed an IFNγ ELISPOT assay to assess MuV-specific T cell responses in peripheral blood mononuclear cells (PBMC) of healthy (vaccinated) donors and mumps patients. Various in vitro MuV-specific stimulation methods of PBMC were compared, using either live or inactivated MuV alone or MuV-infected autologous antigen presenting cells, i.e. Epstein Barr Virus-transformed B lymphoblastoid cell lines (EBV-BLCL) or (mitogen pre-activated) PBMC, for their ability to recall IFNγ-producing responder cells measured by ELISPOT. For the detection of MuV-specific T cell responses, direct exposure (24h) to live MuV was the preferred stimulation method when assay sensitivity and practical reasons were considered. Notably, flowcytometric confirmation of data revealed that primarily T cells and NK cells produce IFNγ upon live MuV stimulation. Depleting PBMC from CD56(+) NK cells prior to stimulation with live MuV led to the enumeration of MuV-specific T cell responses by ELISPOT. Our assay constitutes a tool to evaluate memory MuV-specific T cell responses in MuV vaccinated or infected persons. Furthermore, this study provides evidence that live MuV not only induces IFNγ production by T cells, but also by NK cells.

Immune status of health care workers to measles virus: evaluation of protective titers in four measles IgG EIAs.

BACKGROUND: Following the recognition of a measles case in a hospital in The Netherlands, health care workers (HCW) from the premises were screened by a commercial enzyme immunoassay (EIA) for measles IgG to identify persons at risk for measles. At least 10% of the HCW were tested measles IgG-negative. As this was considered an unusually high proportion, we hypothesized suboptimal sensitivity of EIAs, especially in medical personnel that had vaccine-induced immunity rather than antibodies resulting from natural infection. OBJECTIVES: To determine (vaccine-induced) measles immunity in HCW, using different EIAs compared to the plaque reduction neutralization (PRN) test, the best surrogate marker for vaccine efficacy and immune protection. STUDY DESIGN: Sera from HCW were tested for measles IgG antibodies in three commercial EIAs, in a bead-based multiplex immunoassay (MIA) and in the PRN test, and evaluated against age and vaccination history of the HCW. RESULTS: Of the 154 HCW, born between 1960 and 1995, 153 (99.4%) had protective levels of measles antibodies (PRN> 120mIU/ml). The three EIAs failed to detect any measles IgG antibodies in approximately 10% of the HCW, while this percentage was approximately 3% for the MIA. Negative IgG results rose to 19% for individuals born between 1975 and 1985, pointing to an age group largely representing vaccinated persons from the first measles vaccination period in The Netherlands. CONCLUSION: The results show limitations in the usefulness of current EIA assays for determining protective measles antibodies in persons with a vaccination history.

Dynamics of the serologic response in vaccinated and unvaccinated mumps cases during an epidemic.

In the last decade, several mumps outbreaks were reported in various countries despite high vaccination coverage. In most cases, young adults were affected who have acquired immunity against mumps solely by vaccination and not by previous wild-type mumps virus infection. To investigate mumps-specific antibody levels, functionality and dynamics during a mumps epidemic, blood samples were obtained longitudinally from 23 clinical mumps cases, with or without a prior history of vaccination, and from 20 healthy persons with no serological evidence of recent mumps virus infection. Blood samples from mumps cases were taken 1-2 months and 7-10 months after onset of disease. Both vaccinated and unvaccinated mumps cases had significantly higher geomean concentrations of mumps-specific IgG (resp. 13,617 RU/ml (95% CI of 9,574-19,367 RU/ml) vs. 1,552 (445-5412) RU/ml at 1-2 months; and 6,514 (5,247-8,088) RU/ml vs. 1,143 (480-2,725) RU/ml at 7-10 months) than healthy controls (169 (135-210) RU/ml) (p = 0.001). Patterns in virus-neutralizing (VN) antibody responses against the mumps vaccine virus were similar, vaccinated and unvaccinated mumps cases had significantly higher ND50 values at both time points of sampling (resp 4,695 (3,779-5,832) RU/ml vs. 1,533 (832-2,825) RU/ml at 1-2 months; 2,478 (1,968-3,122) RU/ml vs. 1,221 (1,029-1,449) RU/ml at 7-10 months) compared with (previously vaccinated) healthy controls (122 (196-76)) RU/ml) (p = 0.001) The unvaccinated mumps cases had significantly lower mumps-specific IgG and VN antibody concentrations at both sampling points compared with previously vaccinated cases, but their antibody concentrations did not differ significantly at the 2 time points. In contrast, the mumps-specific IgG and VN antibody concentrations of the previously vaccinated mumps cases were significantly higher within the first 2 months after onset of mumps and declined thereafter, characteristic for a secondary response. A moderate correlation was found between the level of mumps-specific IgG serum antibodies and VN antibodies for the mumps cases (r = 0.64; p<0.001).

Detection of influenza A virus homo- and heterosubtype-specific memory B-cells using a novel protein microarray-based analysis tool.

The emergence of the A(H1N1) 2009 pandemic influenza virus was initially seen as a major world-wide health concern since a low degree of immunity to this virus strain was anticipated. However, age-specific infection attack rates and age-specific differences in seroresponse indicate that pre-existing immunity may have played a significant role in protection especially in older age groups. This study describes the use of a protein microarray as a multiplex analysis tool for detection of influenza virus H1 strain-specific memory B-cells before and after infection with A(H1N1)pdm09. The discrimination was based on detection of specific antibodies in culture supernatants from polyclonally stimulated B-cells against recombinant influenza virus HA1 proteins representing influenza virus subtypes H1 through H9. The protein microarray proved sensitive and specific for antibody detection in culture supernatants of B-cells, and with the potential to deduce a person's history of infection with particular influenza virus variants, including A(H1N1)pdm09. Blood samples obtained from different age groups prior to the pandemic in 2009 partly showed the presence of B-cells producing antibodies binding to the closely related A(H1N1) 1918 pandemic influenza virus, and of which the magnitude increased with age. These cross-reactive antibodies were produced by single memory B-cells present in these donors, and either bind to epitopes on HA1 which are shared within different H1 strains (homosubtypic response) or shared between different subtypes (heterosubtypic response).