OBJECTIVE:We investigated a chickenpox outbreak that started in an Oregon elementary school in October 2001, after public schools began phasing in a varicella vaccination requirement for enrollment. We sought to determine the rate of varicella vaccination and effectiveness and risk factors for breakthrough disease.

METHODS:A chickenpox case was defined as an acute maculopapulovesicular rash without other explanation occurring from October 30, 2001 through January 27, 2002 in a student without a prior history of chickenpox. We reviewed varicella vaccination records and history of prior chickenpox, and we calculated vaccine effectiveness. We evaluated the effects of age, gender, age at vaccination, and time since vaccination on risk of breakthrough disease (ie, chickenpox occurring>42 days after vaccination).

RESULTS:Of 422 students, 218 (52%) had no prior chickenpox. Of these, 211 (97%) had been vaccinated before the outbreak. Twenty-one cases occurred in 9 of 16 classrooms. In these 9 classrooms, 18 of 152 (12%) vaccinated students developed chickenpox, compared with 3 of 7 (43%) unvaccinated students. Vaccine effectiveness was 72% (95% confidence interval: 3%-87%). Students vaccinated>5 years before the outbreak were 6.7 times (95% confidence interval: 2.2-22.9) as likely to develop breakthrough disease as those vaccinated

CONCLUSIONS:A chickenpox outbreak occurred in a school in which 97% of students without a prior history of chickenpox were vaccinated. Students vaccinated>5 years before the outbreak were at risk for breakthrough disease. Booster vaccination may deserve additional consideration.

Invasive Haemophilus influenzae type b (Hib) disease decreased dramatically after the introduction of conjugate vaccine in routine immunization schedules. We report a case of a fifteen-months-old girl, previously healthy and vaccinated, admitted in the emergency room with fever and vomiting. She was irritable and the Brudzinski's sign was positive. The cerebrospinal fluid (CSF) analysis showed pleocytosis and high protein level. Empiric intravenous antibiotics (ceftriaxone and vancomycin) were administered for suspected bacterial meningitis during 10 days. Serotyping of the Haemophilus influenzae strain found in CSF revealed a serotype b. After one year of follow-up no Hib meningitis sequelae were noted. Despite vaccination compliance and absence of risk factors, invasive Hib disease can occur due to vaccine failure. Efforts to keep the low incidence of invasive Hib disease should be directed to the maintenance of high vaccination coverage rates, combined with the notification and surveillance strategies already implemented in each country.

BACKGROUND:Influenza vaccine is moderately effective for preventing influenza illness. It is not known if vaccination reduces the risk of subsequent hospital admission among patients with vaccine failure and laboratory confirmed influenza illness.

METHODS:Patients in a community cohort presenting with acute respiratory illness were prospectively enrolled and tested for influenza during 8 seasons to estimate seasonal vaccine effectiveness. Hospital admissions within 14 days after illness onset were identified for all participants aged≥20 years with laboratory confirmed influenza. The association between vaccination and hospital admission was examined in a propensity score adjusted logistic regression model. The model was validated by examining the association between vaccination and hospital admission in participants without influenza.

RESULTS:Influenza was identified in 1393 (28%) of 4996 participants. Sixty-two (6%) of 1020 with influenza A and 17 (5%) of 369 with influenza B were hospitalized. Vaccination was not associated with a reduced risk of hospital admission among all participants with influenza [adjusted odds ratio (aOR)=1.08; 95% CI: 0.62, 1.88]; or among those with influenza A (aOR=1.35; 95% CI: 0.71, 2.57) or influenza B (aOR=0.67; 95% CI: 0.21, 2.15). Influenza vaccination was not associated with hospitalization after non-influenza respiratory illness (aOR=1.14; 95% CI: 0.84, 1.54).

CONCLUSIONS:Influenza vaccination did not reduce the risk of subsequent hospital admission among patients with vaccine failure. These findings do not support the hypothesis that vaccination mitigates influenza illness severity.

We investigated a mumps outbreak within a highly vaccinated university student population in the Netherlands by conducting a retrospective cohort study among members of university societies in Delft, Leiden and Utrecht. We used an online questionnaire asking for demographic information, potential behavioural risk factors for mumps and the occurrence of mumps. Vaccine status from the national vaccination register was used. Overall, 989 students participated (20% response rate). Registered vaccination status was available for 776 individuals, of whom 760 (98%) had been vaccinated at least once and 729 (94%) at least twice. The mumps attack rate (AR) was 13.2% (95%CI 11.1-15.5%). Attending a large student party, being unvaccinated and living with more than 15 housemates were independently associated with mumps ((RR 42 (95%CI 10.1-172.4); 3.1 (95%CI 1.7-5.6) and 1.8 (95%CI 1.1-3.1), respectively). The adjusted VE estimate for two doses of MMR was 68% (95%CI 41-82%). We did not identify additional risk factors for mumps among party attendees. The most likely cause of this outbreak was intense social mixing during the party and the dense communal living environment of the students. High coverage of MMR vaccination in childhood did not prevent an outbreak of mumps in this student population.

BACKGROUND:Measles was eliminated in the United States through high vaccination coverage and a public health system able to rapidly respond to measles. Measles may occur among vaccinated individuals, but secondary transmission from such individuals has not been documented.

METHODS:Suspected patients and contacts exposed during a measles outbreak in New York City in 2011 were investigated. Medical histories and immunization records were obtained. Cases were confirmed by detection of measles-specific immunoglobulin M and/or RNA. Tests for measles immunoglobulin G (IgG), IgG avidity, measurement of measles neutralizing antibody titers, and genotyping were performed to characterize the cases.

RESULTS:The index patient had 2 doses of measles-containing vaccine; of 88 contacts, 4 secondary patients were confirmed who had either 2 doses of measles-containing vaccine or a past positive measles IgG antibody. All patients had laboratory confirmation of measles infection, clinical symptoms consistent with measles, and high-avidity IgG antibody characteristic of a secondary immune response. Neutralizing antibody titers of secondary patients reached>80 000 mIU/mL 3-4 days after rash onset and that of the index was<500 mIU/mL 9 days after rash onset. No additional cases of measles occurred among 231 contacts of secondary patients.

CONCLUSIONS:This is the first report of measles transmission from a twice-vaccinated individual with documented secondary vaccine failure. The clinical presentation and laboratory data of the index patient were typical of measles in a naive individual. Secondary patients had robust anamnestic antibody responses. No tertiary cases occurred despite numerous contacts. This outbreak underscores the need for thorough epidemiologic and laboratory investigation of suspected cases of measles regardless of vaccination status.

From January, 1988, to March, 1989, a widespread outbreak (118 cases) of poliomyelitis type 1 occurred in Oman. Incidence of paralytic disease was highest in children younger than 2 years (87/100,000) despite an immunisation programme that recently had raised coverage with 3 doses of oral poliovirus vaccine (OPV) among 12-month-old children from 67% to 87%. We did a case-control study (70 case-patients, 692 age-matched controls) to estimate the clinical efficacy of OPV, assessed the immunogenicity of OPV and extent of poliovirus spread by serology, retrospectively evaluated the cold chain and vaccine potency, and sought the origin of the outbreak strain by genomic sequencing. 3 doses of OPV reduced the risk of paralysis by 91%; vaccine failures could not be explained by failures in the cold chain nor on suboptimum vaccine potency. Cases and controls had virtually identical type 1 neutralising antibody profiles, suggesting that poliovirus type 1 circulation was widespread. Genomic sequencing indicated that the outbreak strain had been recently imported from South Asia and was distinguishable from isolates indigenous to the Middle East. Accumulation of enough children to sustain the outbreak seems to have been due to previous success of the immunisation programme in reducing spread of endemic strains, suboptimum efficacy of OPV, and delay in completing the primary immunisation series until 7 months of age. Additionally, the estimated attack rate of infection among children aged 9-23 months exceeded 25% in some regions, suggesting that a substantial proportion of fully vaccinated children had been involved in the chain of transmission.

Rabies remains a serious public health problem in many developing countries. The diagnosis is easy when a non-immunised patient presents with hydrophobia and hypersalivation after a bite by a known rabid animal but more difficult when a patient presents atypical symptoms after having received rabies postexposure prophylaxis. Rabies postexposure prophylaxis failure is rare. We report a case of a 6-year-old boy who presented febrile seizure with agitation and cerebellar signs, without hydrophobia or hypersalivation, 17 days after a dog bite. Despite four doses of rabies vaccine and immunoglobulin, he died. Diagnostic confirmation of rabies encephalitis was made in post mortem on brain biopsies by fluorescent antibody technique.

Severe (grade III) tetanus occurred in three immunized patients who had high serum levels of anti-tetanus antibody. The disease was fatal in one patient. One patient had been hyperimmunized to produce commercial tetanus immune globulin. Two patients had received immunizations 1 year before presentation. Anti-tetanus antibody titers on admission were 25 IU/ml to 0.15 IU/ml by hemagglutination and ELISA assays; greater than 0.01 IU/ml is considered protective. Even though one patient had seemingly adequate anti-tetanus titers by in vitro measurement (0.20 IU), in vivo mouse protection bioassays showed a titer less than 0.01 IU/ml, implying that there may have been a hole in her immune repertoire to tetanus neurotoxin but not to toxoid. This is the first report of grade III tetanus with protective levels of antibody in the United States. The diagnosis of tetanus, nevertheless, should not be discarded solely on the basis of seemingly protective anti-tetanus titers.

Haemophilus b polysaccharide vaccine was first licensed in the United States in April 1985. Between May 1985 and September 1987, 228 reports of disease due to Haemophilus influenzae in vaccinated children were submitted to the Food and Drug Administration, of which 216 were accepted for analysis. We compared the relative frequencies of the different disease entities caused by H. influenzae type b reported in vaccinated children with those reported in unvaccinated children (greater than 1000 cases that occurred between 1973 and 1984, as reported in the literature). Over 90% of the vaccinated children were greater than or equal to 24 mo of age. A higher proportion of cases was reported to have occurred within the first two months after vaccination, with 10 cases occurring within 72 h of vaccination. Vaccination did not alter the expected frequencies of the different clinical entities associated with invasive H. influenzae disease. No estimates of clinical efficacy are possible based on the adverse events submitted to the Food and Drug Administration.

BACKGROUND:The generalization of the vaccination against H. influenzae b (Hib), according to its integration in the French vaccinal calendar, led to the incidence decrease of the purulent meningitis with Hib in young children, which became a so rare event.

CASE REPORT:We described the case of a 14-months-old child showing a bacterial purulent meningitis with Hib, despite of a well driven vaccination.

DISCUSSION:The epidemiology of bacterial meningitis was upset by the generalization of the anti-H. influenzae b vaccination. The use of combined vaccines specially reduced the incidence and the gravity of this pathology. Nevertheless, in spite of the excellent vaccinal coverage, the limited but real persistence of epiglottis or meningitis due to H. influenzae b should keep in mind of the biologists and the clinicians. Indeed, the chronic nasopharyngal carriage, the existence of not vaccinated or not answering people allow to consider the persistent risk of H. influenzae b bacterial meningitis.