Janet L. Heath

Nonclassic measles infections in an immune population exposed to measles during a college bus trip

This study investigated the frequency of mild or asymptomatic measles infections among 44 persons exposed to a student with measles during a 3‐day bus trip using two buses. Questionnaires and serum samples were obtained 26–37 days after the trip. All participants had detectable measles‐neutralizing antibodies, and none developed classic measles symptoms. Ten persons (23%) were IgM positive for measles, indicating recent infection. Among previously vaccinated IgM‐negative persons, those who rode on bus A with the index case‐patient had significantly higher microneutralization titers than those on bus B (P = .001), suggesting that some persons on bus A were infected but were IgM negative at the time of the study. Mild or asymptomatic measles infections are probably very common among measles‐immune persons exposed to measles cases and may be the most common manifestation of measles during outbreaks in highly immune populations. J. Med. Virol. 56:337–341, 1998.

Risk of infection with hepatitis A, B or C, cytomegalovirus, varicella or measles among child care providers

BACKGROUND Employment as a child care provider has been suggested as an indication for hepatitis A virus (HAV) immunization; however, whether this occupational group is at increased risk of HAV infection is not well-defined. METHODS We obtained sera samples for testing for antibodies to hepatitis A, B and C, cytomegalovirus, varicella and measles from a sample of child care providers in King County, WA, and administered a questionnaire to assess employment characteristics and other potential risk factors for infection. We also compared the anti-HAV seroprevalence among providers with that of subjects in the Third National Health and Nutrition Survey, representative of the US general population. RESULTS Thirteen percent (48 of 360) of providers were anti-HAV-positive (46% (22 of 47) of foreign born vs. 8% (26 of 313) of US-born (P < 0.001)). In multivariate analysis anti-HAV seropositivity was associated with foreign birth, age, income and Hispanic ethnicity but was not associated with characteristics of employment. Seroprevalence among US-born providers tended to be lower than that among Third National Health and Nutrition Survey subjects of similar age, sex, race and income. Sixty-two percent of providers were seropositive to cytomegalovirus, which was associated with nonwhite race, changing diapers > or = 3 days/week while at work and having a child in the household. Antibody prevalence was 1.4% to hepatitis B core antigen, 0.6% to hepatitis C, 94% to measles and 98% to varicella. CONCLUSIONS The anti-HAV prevalence among US-born providers was low, and seropositivity was not associated with employment characteristics, indicating that occupational exposure to HAV is uncommon under non-outbreak circumstances.

Measles vaccine effectiveness and duration of vaccine-induced immunity in the absence of boosting from exposure to measles virus

BACKGROUND It is unknown whether vaccine-induced immunity is lifelong in the absence of periodic exposure to measles virus. After 27 years of no known exposure to measles, an outbreak in Palau in 1993 offered the opportunity to study this issue and the measles vaccine effectiveness. METHODS Household contacts of a sample of confirmed cases were interviewed for exposure, symptoms and vaccination status verified by records. Serum from symptomatic contacts was tested for measles antibodies. RESULTS Among 78 contacts 4 of 5 (80%) unvaccinated, 4 of 35 (11%) 1-dose vaccine recipients and none of 38 (0%) > 1-dose recipients developed measles. Effectiveness of 1-dose vaccine was 86% (95% confidence interval, 60 to 95%). An additional dose significantly reduced the risk of measles (P = 0.048). Time since vaccination was not a significant risk factor for developing measles (relative risk, 1.6; 95% confidence interval, 0.3 to 9.4; persons vaccinated > 15 years ago vs. < 5 years ago). CONCLUSIONS Similar to the estimates previously obtained in the area, measles vaccine effectiveness in Palau was lower than the estimates obtained in the US. A second dose of vaccine further reduced the risk for developing measles. We found no evidence that waning immunity was an important problem in this limited population with no known previous exposure to measles virus. The small number of vaccinated contacts precludes a definitive assessment.

Comparison of Vaccination with Measles-Mumps-Rubella Vaccine at 9, 12, and 15 Months of Age

To determine seroconversion rates with measles-mumps-rubella vaccine administered to children at 9, 12, or 15 months of age, we undertook a prospective randomized trial. Among children vaccinated at 15 months of age, 98% seroconverted to measles, compared with 95% of those vaccinated at 12 months of age and 87% of those vaccinated at 9 months of age. In each age group, children of mothers born in or before 1963 had lower rates of seroconversion against measles, with the lowest rate in children vaccinated at 9 months. The seroconversion rate of rubella paralleled that of measles, with the lowest seroconversion rates in children vaccinated at 9 months of age whose mothers were born in or before 1963. The response to mumps varied little by age of the child or birth year of the childs mother. These results support the recommended age for first vaccination with measles-mumps-rubella at 12-15 months.

Measles outbreaks in Micronesia, 1991 to 1994.

BACKGROUND Several islands in Micronesia experienced large measles outbreaks, during 1991 through 1994. Except for Guam, none of the islands had reported measles outbreaks during the previous 20 years. METHODS To characterize the outbreaks, measles surveillance data, hospital records and death certificates were reviewed. Preoutbreak vaccination coverage rates were assessed by reviewing public health vaccination records. Viral isolates were genetically sequenced to determine the source of transmission. Linear regression analysis was performed to assess the effectiveness of outbreak control measures. RESULTS Between 1991 and 1994 more than 1300 measles cases and 16 measles-related deaths were reported in Micronesia. Preoutbreak vaccination coverage rates among 2-year-old children were 55 to 94%. Genetic sequencing of the viral isolates and epidemiologic investigations suggested transmission between islands and new importations from outside of Micronesia. The highest attack rates were among children ages < 5 years (20/1000) and 10 to 19 years (38/1000). Compared with attack rates among children ages < 1 and 10 to 19 years, attack rates were lower among those ages 5 to 9 years, in whom 2-dose vaccination coverage rates were highest (P < 0.001). Early and rapid implementation of mass vaccination campaigns was significantly associated with shorter duration of outbreaks (P = 0.049). CONCLUSION The measles outbreaks in Micronesia show that island populations may be highly susceptible to measles. High two-dose vaccination coverage levels must be maintained to prevent such outbreaks. Early and rapidly implemented mass measles vaccination campaigns were effective in control of island outbreaks. Strengthening public health infrastructure and surveillance is necessary for early identification of outbreaks and rapid implementation of mass campaigns.

Maternal immunity to measles and infant immunity at less than twelve months of age relative to maternal place of birth

Sera from infants aged 5 to 11 months and from their mothers were used to investigate the level and duration of transplacentally derived measles antibody. The infants of foreign-born, inner-city mothers were more likely to have measles antibody and were less likely to get measles. Infants of foreign-born mothers, because they are less likely to respond to measles vaccine, may require different vaccine strategies than infants of mothers born in the United States.

Measles-Specific IgG Levels in Premature Infants: Efficacy of Vaccination of Seronegative Infants at 9 and 12 Months of Age † 1173

In term infants, maternal antibody may interfere with seroconversion to measles vaccine up to one year of age. This study evaluated the persistence of maternally derived measles antibodies in premature infants and infant response to measles, mumps, rubella (MMRII) vaccination at 9 or 12 months. Serum was collected at birth, 2-4, and 7 months of age from 97 premature infants with birthweights of 1:10. To date, 48 seronegative infants have been randomized to MMRII vaccination at 9 or 12 months old and serum was collected 3 months later. Of 26 infants vaccinated between 8.5 and 10.5 months old, 21/24 (88%) and 25/26 (96%) were seropositive by mNT and EIA, respectively. Of 22 infants vaccinated between 11.5 and 13.5 months old, 18/18 and 22/22 were seropositive by mNT and EIA, respectively. Premature infants are susceptible to measles earlier than term infants and may benefit from early MMRII vaccination. Persistence of antibodies at 18-24 months will be evaluated.