Mortality and morbidity after high titre measles vaccine in Mexico

Beyond vaccine dosage, genetic modifications to the current measles vaccine to overcome maternal passive immunity

Pediatric measles infections still cause an unacceptable rate of childhood mortality. Despite the availability of an efficient preventative vaccine, measles virus can spread among the population of even developed countries. The availability of a reverse genetic system for measles, based on recombinant virus recovery from cDNA, allows application of the principles of intelligent vaccine design. Using this system, we recently demonstrated that a version of the current attenuated measles virus strain genetically modified to express higher levels of the viral hemagglutinin protein, the major target of neutralizing antibodies, is more immunogenic and resists passive immunity with a better immunogenicity profile in a mouse model than the current measles vaccine. The significance and practicality of this development are discussed.

High-titer measles vaccination before 9 months of age and increased female mortality: do we have an explanation?

In 1989, high-titer (HT) Edmonston-Zagreb measles vaccine with a titer more than 10(4.7) plaque-forming-units was recommended by the World Health Organization for use in areas with a high incidence of measles in children younger than 9 months. In 1992, the recommendation was rescinded following reports from Guinea-Bissau, Senegal, and Haiti showing an increased incidence of female mortality occurring after administration of HT Edmonston-Zagreb vaccination. We reviewed 9 studies of HT measles vaccines that reported data on mortality. These reports included 4 randomized trials comparing HT vaccine administered to children younger than 9 months with standard-titer (ST) vaccines (10(3.0) to 10(4.0) plaque-forming-units) given at 9 months of age. Five studies from Zaire, Haiti, Senegal, Rwanda, and Zaire had no control group receiving ST vaccine at 9 months of age, but investigators were able to examine the female-to-male mortality ratio within these HT studies. Investigators have hypothesized that HT vaccine had caused immune suppression similar to that of measles infection. The present review suggests first that the HT vaccine itself is unlikely to be the cause because the effect was not found in all studies. Second, the increased mortality started only after 9 to 10 months of age when controls received ST measles vaccine, and HT groups received the "control vaccine." It was not found in the studies that provided another measles vaccine instead of control vaccine. Third, because the HT studies with excess mortality rates showed increased female mortality rates, we need to find environmental or contextual conditions associated with increased female mortality rates in some studies to explain the problem associated with HT measles vaccination.

No evidence for short or long term morbidity after increased titer measles vaccination in Sudan

BACKGROUND

Increased mortality rates have been reported after high titer measles [>10(5.0) plaque-forming units (PFU)] vaccination in several large studies in the developing world. An increased titer measles vaccine study conducted in Sudan included a prolonged prospective evaluation of childhood morbidity after vaccination.

METHODS

Five hundred ten children (170 per group) were randomized to receive 1 of 3 regimens at 5 and 9 months of age: (1) meningococcal vaccine, then standard titer (50% tissue culture-infective dose, 103.8) Schwarz measles vaccine; (2) increased titer (10(4.7) PFU) Edmonston-Zagreb measles vaccine followed by meningococcal vaccine; and (3) increased titer (10(4.7) PFU) Connaught vaccine followed by standard titer Schwarz measles vaccine.

RESULTS

Health workers collected information at 31,582 semi-monthly and monthly visits during 5 years. No increase in infant mortality was observed, but the statistical power was limited. There were 13, 13 and 10 deaths in the Schwarz, Edmonston-Zagreb and Connaught groups, respectively. There were no differences in duration or incidence of illness between groups at any time during the 5-year follow-up, with comparisons stratified by age and sex. Statistical power for each pairwise comparison was good, with at least 80% power to detect a difference of 1 day per month of illness and a 12% difference in the proportion of visits with an illness recorded.

CONCLUSIONS

We were unable to document increased morbidity in recipients of the increased titer measles vaccines used in this study. These data do not support the hypothesis that increased mortality after increased titer vaccine exposure is the result of increased and cumulative morbidity.

Immunogenicity and safety of standard-titer AIK-C measles vaccine in nine-month-old infants

Because of the interference by maternal antibody before 1 year of age, the Schwarz strain of measles vaccine, which has been routinely used in Taiwan, must be given at 9 months and 15 months of age to ensure an optimal immune response. The AIK-C strain of measles vaccine has been reported to be highly immunogenic. This study evaluated the immunogenicity and safety of the AIK-C vaccine in 9-month-old Taiwanese infants. A total of 135 infants were recruited and were randomly assigned to receive either Schwarz vaccine (68 cases) or AIK-C vaccine (67 cases). Measles antibodies were assayed before and 1 month after the vaccination. Sixty-five (97%) infants who received the AIK-C vaccine seroconverted after the vaccination, whereas the seroconversion rate in those receiving the Schwarz vaccine was 77% (P = 0.001). The incidences of adverse reactions were comparable between the two groups. We conclude that even in 1990s, the failure rate of Schwarz vaccine in 9-month-old infants is still high. The AIK-C vaccine is more immunogenic in infants and its long-term immunogenicity and safety deserve further evaluation.

Measles vaccines: a review of adverse events

A great deal of controversy has recently been generated over the publication of several articles implicating measles vaccine in the induction of Crohn's disease and autism. The publication of this work has already had a negative impact on measles vaccine acceptance in the UK. These allegations are particularly troubling because they arise in the context of increased use of measles vaccine as global control of measles nears and the international community considers strategies for a drive towards eradication. In 1994, the US Institute of Medicine reviewed the world literature and published a comprehensive review of adverse events associated with measles-containing vaccines. Reviewing the literature published between 1994 and the present day, reveals that there is considerable new data suggesting that modified gelatin rather than egg proteins is responsible for most episodes of anaphylaxis following measles vaccination. New work weakens the possible links between measles vaccine and subacute sclerosing panencephalitis and Guillain-Barré syndrome, but strengthens the rare association of measles-containing vaccines with post infectious encephalomyelitis. The alleged associations between measles vaccination and Crohn's disease and autism are based upon weak science and have largely been refuted by a large volume of stronger work. A review of the data generated in the last 4 years amply demonstrates the continued efforts of the scientific community to monitor and understand true measles vaccine-associated adverse events. The rapidity and clarity of this same community's debunking of the spurious associations with Crohn's disease and autism suggests that those charged with vaccination programmes have learned from past mistakes. During 30 years of worldwide use, measles vaccination has proven to be one of the safest and most successful health interventions in the history of mankind. It is not a 'perfect' vaccine, but the benefits of measles vaccination far outweigh the risks even in countries with low incidence of measles and high rates of measles vaccine coverage.

A comparison of vaccine efficacy and mortality during routine use of high-titre Edmonston-Zagreb and Schwarz standard measles vaccines in rural Senegal

Vaccine efficacy and mortality in successive cohorts of children who routinely received either Edmonston-Zagreb high-titre (EZ-HT) or Schwarz standard (SW-STD) measles vaccines have been examined in a rural area of Senegal. The 2 vaccines were equally protective against measles infection (vaccination efficacy: EZ-HT 94%; SW-STD 93%). Children who did not attend a scheduled session to receive measles vaccine had a higher mortality rate between 9 months and 2 years of age than did children receiving either EZ-HT (mortality ratio [MR] = 1.81, 95% confidence interval [CI] 1.06-3.08) or SW-STD measles vaccine (MR = 1.74, 95% CI 0.95-3.21). Children of either sex vaccinated with EZ-HT had lower mortality than their equivalents who had not received any measles vaccine. There was no difference in overall mortality between recipients of EZ-HT and SW-STD (MR = 0.96, 95% CI 0.70-1.30). Using a Cox regression analysis to adjust for sex, age and significant background factors (season and death of mother), mortality rates tended to be lower for male recipients of EZ-HT than for boys receiving SW-STD (MR = 0.73, 95% CI 0.50-1.11) and higher for girls receiving EZ-HT than for girls receiving SW-STD (MR = 1.30, 95% CI 0.81-2.09) (test of interaction between sex and vaccine, P = 0.067). The tendency to reduced survival benefit for girls following receipt of high-titre measles vaccines substantiated observations from randomized trials in Guinea-Bissau, Senegal and Haiti. Existing data provide little support for the notion that high-titre vaccine is deleterious but it may not have the same beneficial effects as standard-titre measles vaccine.

Five year follow-up of morbidity and mortality among recipients of high-titre measles vaccines in Senegal

At 3-5 years of age, female recipients of Edmonston-Zagreb high-titre (EZ-HT) and Schwarz high-titre (SW-HT) measles vaccine had lower survival rates than female recipients of Schwarz standard measles vaccine (SW-STD) in Guinea-Bissau, Senegal and Haiti. In Senegal, the children who received high-titre vaccines have now been followed to the age of 5-7 years to determine whether the difference in mortality persisted, and whether differences in vaccine efficacy were apparent. At this age there was no difference in mortality between female recipients of high-titre and standard titre measles vaccines. There was no indication that high-titre EZ-HT vaccine at 5 months (EZ-HT,5m) provided suboptimal protection, as vaccine efficacy after exposure was 97% and 95%, respectively, for EZ-HT,5m and SW-STD,10m vaccines, whereas SW-HT,5m vaccine had an efficacy of 81%. The difference in mortality between recipients of high-titre vaccines and SW-STD observed in several studies during the first few years after vaccination may be explained by non-specific beneficial effects of the standard measles vaccine rather than a harmful effect of the high-titre vaccines.