Tapani Hovi

Expert Review on Poliovirus Immunity and Transmission

Successfully managing risks to achieve wild polioviruses (WPVs) eradication and address the complexities of oral poliovirus vaccine (OPV) cessation to stop all cases of paralytic poliomyelitis depends strongly on our collective understanding of poliovirus immunity and transmission. With increased shifting from OPV to inactivated poliovirus vaccine (IPV), numerous risk management choices motivate the need to understand the tradeoffs and uncertainties and to develop models to help inform decisions. The U.S. Centers for Disease Control and Prevention hosted a meeting of international experts in April 2010 to review the available literature relevant to poliovirus immunity and transmission. This expert review evaluates 66 OPV challenge studies and other evidence to support the development of quantitative models of poliovirus transmission and potential outbreaks. This review focuses on characterization of immunity as a function of exposure history in terms of susceptibility to excretion, duration of excretion, and concentration of excreted virus. We also discuss the evidence of waning of host immunity to poliovirus transmission, the relationship between the concentration of poliovirus excreted and infectiousness, the importance of different transmission routes, and the differences in transmissibility between OPV and WPV. We discuss the limitations of the available evidence for use in polio risk models, and conclude that despite the relatively large number of studies on immunity, very limited data exist to directly support quantification of model inputs related to transmission. Given the limitations in the evidence, we identify the need for expert input to derive quantitative model inputs from the existing data.

Etiology of measles- and rubella-like illnesses in measles, mumps, and rubella-vaccinated children

The viral etiology of measles- or rubella-like illnesses after MMR (measles, mumps, and rubella) vaccination was studied prospectively in 993 acutely ill Finnish children with fever and rash in 1983-1995. Their sera were tested for adeno-, entero-, and parvovirus B19 antibodies. Sera of 300 children <4 years old were also tested for human herpesvirus 6 (HHV-6) antibodies. Measles and rubella had been excluded by previous antibody testing. Serologic diagnosis of adeno-, entero-, or parvovirus infection was based on EIA (IgM or IgG antibodies) and that of HHV-6 on indirect immunofluorescence. A viral etiology was verified in 368 cases, most commonly parvovirus (20%), followed by enterovirus (9%) and adenovirus (4%). Among young children, HHV-6 infection was found in 37 (12%). Thirty-eight children (4%) had double infections. This study confirms that measles- or rubella-like illnesses in MMR-vaccinated children are often caused by other viruses. Each suspected vaccine failure requires laboratory confirmation to maintain reliable surveillance and control and to establish the specific etiology of the disease.

Viral Etiology of Frequently Recurring Respiratory Tract Infections in Children

The viral etiology of frequently recurring respiratory tract infection (FRRI) in children aged <2 years was studied. Altogether, 329 children were followed from 2 to 24 months of age in the Finnish Otitis Media Cohort Study. Children with FRRI were defined as having > or =9 episodes of upper respiratory tract infection (URI) and/or > or =4 episodes of acute otitis media during follow-up. Nasopharyngeal aspirates, middle ear fluid specimens, and serum samples were analyzed for 8 common respiratory viruses. Of 1358 URI episodes, 642 (47%) occurred in the 78 children with FRRI. At least 1 virus was associated with 62% of these episodes, whereas the corresponding figure for children without FRRIs was 54%. The frequency of different viruses was similar in both groups, but the relative proportion of rhinovirus infections was slightly higher among children with FRRI. In conclusion, a specific viral etiology does not explain the excess of URI episodes in children with FRRI.

Loss of protective immunity to polio, diphtheria and Haemophilus influenzae type b after allogeneic bone marrow transplantation

Immunity to poliovirus, diphtheria and Haemophilus influenzae type b (Hib) was studied in 16 adult recipients of a bone marrow transplant from an HLA‐identical sibling donor in order to evaluate the need for revaccinations. T‐cell depletion was not done in any case. The donors and patients were studied before bone marrow transplantation (BMT) and the patients 1, 3, 6, and 12 months later. Prior to the BMT 10 of 11 patients were immune (titre ≥ 4) to all vaccine poliovirus types by a standard microneutralization assay. At 12 months after BMT only two of seven patients were immune to all vaccine types, and none had immunity against an antigenically altered poliovirus type 3 strain Finland. The geometric means of antibody titres against poliovirus types 1, 2, and 3 strain Saukett and strain Finland declined gradually after 1 month postgrafting, being 4.4, 5.4, 3.3, and 1.3 respectively at 12 months after BMT. At 1 year 6 of 11 patients had immunity against diphtheria by a toxin neutralization method, but the antitoxin geometric mean level had decreased to a barely protective level, 0.01 IU/ml. The geometric mean Hib antibody concentration decreased during the first 6 months after BMT and thereafter increased slightly. A significant proportion of BMT recipients lose their protection against polio, diphtheria and Hib, and revaccinations are necessary.

Review and Assessment of Poliovirus Immunity and Transmission: Synthesis of Knowledge Gaps and Identification of Research Needs

With the intensifying global efforts to eradicate wild polioviruses, policymakers face complex decisions related to achieving eradication and managing posteradication risks. These decisions and the expanding use of inactivated poliovirus vaccine (IPV) trigger renewed interest in poliovirus immunity, particularly the role of mucosal immunity in the transmission of polioviruses. Sustained high population immunity to poliovirus transmission represents a key prerequisite to eradication, but poliovirus immunity and transmission remain poorly understood despite decades of studies. In April 2010, the U.S. Centers for Disease Control and Prevention convened an international group of experts on poliovirus immunology and virology to review the literature relevant for modeling poliovirus transmission, develop a consensus about related uncertainties, and identify research needs. This article synthesizes the quantitative assessments and research needs identified during the process. Limitations in the evidence from oral poliovirus vaccine (OPV) challenge studies and other relevant data led to differences in expert assessments, indicating the need for additional data, particularly in several priority areas for research: (1) the ability of IPV-induced immunity to prevent or reduce excretion and affect transmission, (2) the impact of waning immunity on the probability and extent of poliovirus excretion, (3) the relationship between the concentration of poliovirus excreted and infectiousness to others in different settings, and (4) the relative role of fecal-oral versus oropharyngeal transmission. This assessment of current knowledge supports the immediate conduct of additional studies to address the gaps.

Effect of Host Proteases on Early Steps of Enterovirus Infection

Enteroviruses, a genus in the family of Picornaviridae,are small non-enveloped animal viruses with a messenger-sense genomic RNA and an icosahedral capsid composed of 60 copies each of four structural proteins.1 There are about 70 different serotypes of enteroviruses isolated from man and a lot of others that infect domestic or wild animals. Because of their significance in public health the three serotypes of polioviruses, the causative agents of poliomyelitis, have been as targets of the most intensive research during the last a few decades. Other enteroviruses, although known for long to be medically important as well, have only recently acquired more specific attention. These studies have revealed interesting individual characteristics of various non-polio enteroviruses on top of the previously known antigenic differences.1–4