Protecting the vaccinating population in the face of a measles epidemic: assessing the impact of adjusted vaccination schedules

The repertoire of maternal anti-viral antibodies in human newborns

All circulating immunoglobulin G (IgG) antibodies in human newborns are of maternal origin¹ and transferred across the placenta to provide passive immunity until newborn IgG production takes over 15 weeks after birth². However, maternal IgG can also negatively interfere with newborn vaccine responses³. The concentration of IgG increases sharply during the third trimester of gestation and children delivered extremely preterm are believed to largely lack this passive immunity^1,2,4. Antibodies to individual viruses have been reported^5-12, but the global repertoire of maternal IgG, its variation in children, and the epitopes targeted are poorly understood. Here, we assess antibodies against 93,904 epitopes from 206 viruses in 32 preterm and 46 term mother-child dyads. We find that extremely preterm children receive comparable repertoires of IgG as term children, albeit at lower absolute concentrations and consequent shorter half-life. Neutralization of the clinically important respiratory syncytial virus (RS-virus) was also comparable until three months of age. These findings have implications for understanding infectious disease susceptibility, vaccine development, and vaccine scheduling in newborn children.

Searching for the human genetic factors standing in the way of universally effective vaccines

Vaccines have revolutionized modern public health. The effectiveness of some vaccines is limited by the variation in response observed between individuals and across populations. There is compelling evidence that a significant proportion of this variability can be attributed to human genetic variation, especially for those vaccines administered in early life. Identifying and understanding the determinants of this variation could have a far-reaching influence upon future methods of vaccine design and deployment. In this review, we summarize the genetic studies that have been undertaken attempting to identify the genetic determinants of response heterogeneity for the vaccines against hepatitis B, measles and rubella. We offer a critical appraisal of these studies and make a series of suggestions about how modern genetic techniques, including genome-wide association studies, could be used to characterize the genetic architecture of vaccine response heterogeneity. We conclude by suggesting how the findings from such studies could be translated to improve vaccine effectiveness and target vaccination in a more cost-effective manner.

Waning of maternal antibodies against measles, mumps, rubella, and varicella in communities with contrasting vaccination coverage

BACKGROUND

The combined measles, mumps, and rubella (MMR) vaccine has been successfully administered for >20 years. Because of this, protection by maternal antibodies in infants born to vaccinated mothers might be negatively affected.

METHODS

 A large cross-sectional serologic survey was conducted in the Netherlands during 2006-2007. We compared the kinetics of antibody concentrations in children and women of childbearing age in the highly vaccinated general population with those in orthodox Protestant communities that were exposed to outbreaks.

RESULTS

 The estimated duration of protection by maternal antibodies among infants in the general population, most of whom were born to vaccinated mothers, was short: 3.3 months for measles, 2.7 months for mumps, 3.9 months for rubella, and 3.4 months for varicella. The duration of protection against measles was 2 months longer for infants born in the orthodox communities, most of whom had unvaccinated mothers. For rubella, mothers in the orthodox communities had higher concentrations of antibodies as compared to the general population.

CONCLUSION

 Children of mothers vaccinated against measles and, possibly, rubella have lower concentrations of maternal antibodies and lose protection by maternal antibodies at an earlier age than children of mothers in communities that oppose vaccination. This increases the risk of disease transmission in highly vaccinated populations.

Measles outbreak in Europe: susceptibility of infants too young to be immunized

As women vaccinated against measles transfer low amounts of antibodies, an increasing number of infants lack early protection through maternal antibodies until being immunised themselves. This paper reviews the literature on disease burden of measles in the population too young to be immunized according to the respective national recommendations during recent outbreaks in EU and EEA/EFTA countries. In addition, specific control strategies adopted to protect this young population are reviewed. Pubmed, Unbound Medline, Web of Knowledge and the Eurosurveillance database were searched using MESH terms: measles and epidemiology, measles and infants, prevalence of measles, measles and outbreaks and measles and epidemic. Additionally, data from Euvac.net and ECDC were consulted. Databases were searched from January 2001 to September 2011. Fifty-three papers were included in the analysis. The percentage of all measles cases during outbreaks affecting young infants ranged from 0.25% to 83.0%. Specific control strategies were adopted: e.g. administration of the first or second vaccine dose earlier than recommended. Infants younger than 12 months are often involved in measles outbreaks, and advancing the first vaccine dose could reduce the burden of disease. However, immunization before 9 months of age is not systematically recommended because of dysmature humoral immune responses of infants. High coverage and timely administration of the recommended series of vaccines are the most important measures to decrease measles incidence and measles circulation and protect vulnerable infants from infection.

Measles, mumps and rubella infections and atopic disorders in MMR-unvaccinated and MMR-vaccinated children

Vaccinations have been incriminated in the increase of atopic disorders. Especially the measles-mumps-rubella (MMR) vaccination is often refused by people having a notion that these infectious diseases are beneficial for a healthy development of a child's immune system. This practice endangers herd immunity and is the cause of repeated outbreaks. As the clinical course of infections and also its possible impact on the development of atopy may be different in vaccinated and unvaccinated individuals, we explored in vaccinated and unvaccinated children associations of MMR infection with atopic disorders. Using data from a previously conducted study on the relationship between the diphtheria-tetanus-pertussis-(inactivated) poliomyelitis vaccination in the first year of life and atopic disorders, the study population of 1872 8-12-yr-old was divided as children MMR-unvaccinated and children MMR-vaccinated in the first year of life. Within each group the association between MMR infections and atopic disorders (both as reported by the parents) was assessed. We found a statistically significant positive association between measles infection and 'any atopic disorder' [adjusted odds ratio, OR (95% confidence interval, CI): 1.77 (1.20-2.61)] in the MMR-vaccinated group, mainly because of the relationship with eczema. For rubella there was a negative association with eczema and food allergy in the unvaccinated group: adjusted OR (95% CI): 0.57 (0.38-0.85) and 0.23 (0.07-0.76), respectively. All other associations were not statistically significant. We found a positive relationship between measles infection and any atopy in a group of MMR-vaccinated children and a negative association between rubella infection and eczema and food allergy in unvaccinated children. However, we cannot conclude that these relationships are causal. The negative association with rubella may be an artefact. This study shows no evidence for any protective effects from MMR diseases for the development of atopy and therefore supports conclusions found elsewhere that childhood vaccinations do not cause atopy.

Maternal antibody inhibits both cellular and humoral immunity in response to measles vaccination at birth

Maternal antibody prevents the use of live, attenuated measles vaccine (LAV) before 6-9 months of age, but vaccinated 6-month-old infants can mount a T cell response. An infant macaque model was used to study the immune response to LAV in the newborn in the presence or absence of maternal antibody. Four newborn monkeys without detectable maternal antibody and 9 newborns with passive measles antibody were vaccinated with LAV. Only the infants without passive antibody seroconverted after vaccination and 3 of 4 of these infants also developed measles-specific interferon gamma+ T cells. The monkeys were challenged with wild-type measles virus at 5 months of age, and 7 of 9 infants vaccinated in the presence of passive antibody had systemic infection and skin rash, while 3 of the 4 infants vaccinated in the absence of passive antibody were protected from viremia and rash. This suggests that the newborn can respond to LAV but that maternal antibody suppresses the priming of both humoral and cellular immunity at birth.

Immunity against measles in populations of women and infants in Poland

During the 1997-1998 measles epidemic in Poland a high attack rate occurred in infants up to 1 year of age (24.6/100,000 in comparison with 5.5/100,000 in total population). Routine vaccination against measles for infants aged 13-15 months was introduced in Poland in 1975, and a second dose added in 1991. The recommended age for measles vaccination was based on information gathered in years when most mothers had a natural measles. Nowadays, many mothers have received measles vaccine. Early loss of passively acquired measles antibody may occur in infants of women who received measles vaccine, because measles vaccine induces lower antibody titres than does natural infection. Therefore, measles-specific antibody titres were determined among vaccinated and unvaccinated women as well as among infants, whose mothers were born after 1976 and likely were vaccinated (Group 1), and those, whose mothers were born before 1969 and likely have had a natural measles (Group 2). All women that were born in prevaccination era had significantly higher geometric mean titre (GMT) of measles antibody than those who were vaccinated (P<0.001). Also infants from Group 2 at every age had higher GMT of measles antibody than those of Group 1. The antibody decay was significantly faster among infants whose mothers acquired immunity by measles vaccination. Because nowadays the majority of women in childbearing age are vaccinated against measles, earlier vaccination in the infants should be considered.

Reconstruction of measles dynamics in a vaccinated population

The evaluation of measles vaccination programmes has been problematic because the change in actual numbers of infections and susceptibles over time cannot be directly observed. In this paper, we present a method for estimating the time series of number of susceptibles and infections, as well as the critical vaccination coverage in a vaccinated population. The proposed method is applied to data on measles outbreaks in The Netherlands. We show that the results are self-consistent and in line with available independent estimates. A potential application of the proposed method lies in detecting the loss of herd immunity and assessing the risk of major outbreaks in vaccinated populations.

Antibody dynamics in childhood diseases: waning and boosting of immunity and the impact of vaccination

The introduction of vaccination against acute diseases such as measles induced a dramatic decline in the prevalence of the disease, and a more gradual rise in the proportion of the population whose immunity is derived solely from vaccination. These two factors combine to constitute an important shift in the dynamics of immunity, especially in highly vaccinated populations. We develop a general model to describe both loss of immunity in the absence of disease, and boosting of immunity corresponding to subclinical infection in individuals whose immunity has waned. We consider the interaction between infection and immunity and identify the key parameters that determine the eradication threshold. We explore the dynamics in the years following the introduction of vaccination using a stochastic version of the model, and consider the effect of different assumptions concerning the nature of immunity. A comparison of the model results with recently published data suggests that heterogeneity in host immune response is an important feature of the antibody dynamics.