It has been suggested that the incidence of herpes zoster may increase due to lack of natural boosting under large-scale vaccination with the varicella vaccine. To study the possibility and magnitude of such negative consequences of mass vaccination, we built a mathematical model of varicella and zoster epidemiology in the Finnish population. The model was based on serological data on varicella infection, case-notification data on zoster, and new knowledge about close contacts relevant to transmission of infection. According to the analysis, a childhood programme against varicella will increase the incidence of zoster by one to more than two thirds in the next 50 years. This will be due to increase in case numbers in the 35 years age groups. However, high vaccine coverage and a two-dose programme will be very effective in stopping varicella transmission in the population.

BackgroundDay care centre (DCC) attendees play a central role in maintaining the circulation of Streptococcus pneumoniae (pneumococcus) in the population. Exposure within families and within DCCs are the main risk factors for colonisation with pneumococcal serotypes in DCC attendees.MethodsTransmission of serotype specific carriage was analysed with a continuous time event history model, based on longitudinal data from day care attendees and their family members. Rates of acquisition, conditional on exposure, were estimated in a Bayesian framework utilising latent processes of carriage. To ensure a correct level of exposure, non-participating day care attendees and their family members were included in the analysis. Posterior predictive simulations were used to quantify transmission patterns within day care cohorts, to estimate the basic reproduction number for pneumococcal carriage in a population of day care cohorts, and to assess the critical vaccine efficacy against carriage to eliminate pneumococcal transmission.ResultsThe model, validated by posterior predictive sampling, was successful in capturing the strong temporal clustering of pneumococcal serotypes in the day care cohorts. In average 2.7 new outbreaks of pneumococcal carriage initiate in a day care cohort each month. While 39% of outbreaks were of size one, the mean outbreak size was 7.6 individuals and the mean length of an outbreak was 2.8 months. The role of families in creating and maintaining transmission was minimal, as only 10% of acquisitions in day care attendees were from family members. Considering a population of day care cohorts, a child-to-child basic reproduction number was estimated as 1.4 and the critical vaccine efficacy against acquisition of carriage as 0.3.ConclusionPneumococcal transmission occurs in serotype specific outbreaks of carriage, driven by within-day-care transmission and between-serotype competition. An amplifying effect of the day care cohorts enhances the spread of pneumococcal serotypes within the population. The effect of vaccination, in addition to reducing susceptibility to pneumococcal carriage in the vaccinated, induces a herd effect, thus creating a counter-effect to the amplifying effect of the cohort. Consequently, the critical vaccine efficacy against carriage, required for elimination of transmission, is relatively low. Use of pneumococcal conjugate vaccines is expected to induce a notable herd protection against pneumococcal disease.

This article describes a widespread outbreak of hepatitis A virus (HAV) infection amongst drug abusers in Finland. Although attempts to demonstrate the virus in amphetamines failed, the infection was assumed to be linked to intravenous use of the drug. The unusual mode of transmission prompted us to analyse possible atypical clinical features as well as the spread of the virus to the general population, nowadays practically without protective immunity. Serologically verified cases that occurred in Helsinki were interviewed, their hospital records were analysed and their contacts were serology tested. Amphetamine lots, as well as faecal samples from patients, were examined with RT-PCR. Detailed information was obtained from 238 subjects, among whom 131 admitted drug abuse and 67 cases were classified as secondary cases. Phylogenetic analysis of virus strains from HAV-infected cases suggested a common origin, and epidemiological observations linked it with particular lots of amphetamine. Three cases died, and 3 presented with severe clinical disease. Icterus was more common among i.v. drug abusers than others. Infection with hepatitis A virus was probably related to the faecal contamination of amphetamine associated with the transportation of the drugs in the gastrointestinal tract.

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Our results suggest that oral rotavirus vaccination is considered safe in the individuals at risk of CD and T1D.