Effect of mass immunization against influenza encephalopathy on mortality rates in children

Addressing vaccine-preventable encephalitis in vulnerable populations

PURPOSE OF REVIEW

Vaccinations have been pivotal in lowering the global disease burden of vaccine-preventable encephalitides, including Japanese encephalitis, tick-borne encephalitis, measles encephalitis, and rabies encephalitis, among others.

RECENT FINDINGS

Populations vulnerable to vaccine-preventable infections that may lead to encephalitis include those living in endemic and rural areas, military members, migrants, refugees, international travelers, younger and older persons, pregnant women, the immunocompromised, outdoor, healthcare and laboratory workers, and the homeless. There is scope for improving the availability and distribution of vaccinations, vaccine equity, surveillance of vaccine-preventable encephalitides, and public education and information.

SUMMARY

Addressing these gaps in vaccination strategies will allow for improved vaccination coverage and lead to better health outcomes for those most at risk for vaccine-preventable encephalitis.

Severe Influenza-Associated Neurological Disease in Australian Children: Seasonal Population-Based Surveillance 2008-2018

BACKGROUND

Influenza-associated neurological disease (IAND) is uncommon but can result in death or neurological morbidity in children. We aimed to describe the incidence, risk factors, and outcome of children with IAND from seasonal influenza in Australia.

METHODS

We analyzed national, population-based, surveillance data for children aged ≤ 14 years with severe influenza and neurological involvement, over 11 Australian influenza seasons, 2008-2018, by the Australian Paediatric Surveillance Unit.

RESULTS

There were 633 laboratory-confirmed cases of severe influenza reported. Of these, 165 (26%) had IAND. The average annual incidence for IAND was 3.39 per million children aged ≤ 14 years. Compared to cases without neurological complications, those with IAND were more likely to have a pre-existing neurological disease (odds ratio [OR] 3.03, P < .001), but most children with IAND did not (n = 135, 82%). Children with IAND were more likely to receive antivirals (OR 1.80, P = .002), require intensive care (OR 1.79, P = .001), require ventilation (OR 1.99; P = .001), and die (OR 2.83, P = .004).

CONCLUSIONS

IAND is a preventable cause of mortality, predominantly in otherwise well children. Incidence estimates validate previous sentinel site estimates from Australia. IAND accounted for a quarter of all severe influenza, is associated with intensive care unit admission, and accounted for half of all influenza deaths.

Influenza-associated Neurologic Complications in Hospitalized Pediatric Patients: A Multicenter Retrospective Study in Republic of Korea

BACKGROUND

The rates of influenza-associated neurologic complications are variable among studies, and a difference has been observed between the Western and Asian countries. The study aims to evaluate the frequency and characteristics of influenza-associated neurologic complications.

METHODS

We performed a retrospective review of hospitalized cases of influenza infection from October 2010 to April 2017 from 3 referral hospitals.

RESULTS

A total of 1988 influenza cases were identified. Influenza-associated neurologic complications were 161 cases (8.1%); influenza virus A was detected in 113 (70.2%) cases, B in 47 (29.2%) cases and both A and B in 1 case (0.6%). Twenty-four patients (15%) had underlying neurologic diseases. The most common diagnosis was a simple febrile convulsion (44%), followed by complex febrile convulsion (29%), fever-provoked seizure under pre-existing neurologic disease or afebrile seizure (14%), encephalopathy/encephalitis (8%) and meningitis (5%). Most of the patients fully recovered (96%). Three patients (1.9%) died of myocarditis (n = 1), encephalopathy (n = 1), and simultaneous encephalitis and myocarditis (n = 1). Pre-existing neurologic disease, age groups of 6 months to 6 years and 6-12 years were a risk factor of influenza-associated neurologic complications with an adjusted odds ratio of 5.41 (95% confidence interval [CI] 3.23-9.06, P < 0.001), 12.99 (95% CI 1.77-95.19, P = 0.01) and 8.54 (95% CI 1.14-64.79, P = 0.04), respectively. There was no association between neuropsychiatric adverse events and oseltamivir prescription (P = 0.17).

CONCLUSIONS

Influenza-associated neurologic complications are not uncommon, and most patients fully recovered. The frequency of influenza-associated neurologic complications in Korean children was not significantly different from that of children in Western countries.

Heterogeneity of Antiviral Responses in the Upper Respiratory Tract Mediates Differential Non-lytic Clearance of Influenza Viruses

Influenza viruses initiate infection in the upper respiratory tract (URT), but early viral tropism and the importance of cell-type-specific antiviral responses in this tissue remain incompletely understood. By infecting transgenic lox-stop-lox reporter mice with a Cre-recombinase-expressing influenza B virus, we identify olfactory sensory neurons (OSNs) as a major viral cell target in the URT. These cells become infected, then eliminate the virus and survive in the host post-resolution of infection. OSN responses to infection are characterized by a strong induction of interferon-stimulated genes and more rapid clearance of viral protein relative to other cells in the epithelium. We speculate that this cell-type-specific response likely serves to protect the central nervous system from infection. More broadly, these results highlight the importance of evaluating antiviral responses across different cell types, even those within the same tissue, to more fully understand the mechanisms of viral disease.

Characteristics and outcome of influenza-associated encephalopathy/encephalitis among children in a tertiary pediatric hospital in Italy, 2017-2019

Background

Influenza is the most frequent cause of acute upper respiratory tract infections during winter season. Although rare, neurological manifestations are known to occur during influenza infection and approximatively three-quarters of cases are in children. In this study, we aimed to characterize the burden and clinical spectrum of influenza-associated encephalopathy and encephalitis in children admitted at a tertiary pediatric hospital in Italy over two influenza seasons (2017–2019).

Methods

We retrospectively analyzed clinical, laboratory, instrumental data and outcome of patients discharged with ICD9-CM 487.0 code.

Results

Fifteen children (13.1% of those discharged with a diagnosis of influenza infection in the study period), had influenza-associated central nervous system (CNS) manifestations. Eight patients (53.3%) were diagnosed as influenza encephalitis, 7 (46.7%) as influenza encephalopathy. Median age was 27 months. In children under 2 years of age (40% of all cases) altered consciousness was the most frequent neurological manifestation while respiratory symptoms were present at admission in all cases. Younger children also required intensive care support more frequently. Five subjects (33.3%) presented comorbidity. None of the patients had received seasonal influenza vaccination. The median time from onset of respiratory signs to onset of neurological manifestations was 24 h. Cerebrospinal fluid (CSF) analysis was normal in most patients and polymerase chain reaction for influenza virus RNA on CSF, when performed, was negative in all samples. Neuroradiological investigations, performed in 5 children, reported cortical and subcortical white matter signal alterations. Oseltamivir was administered only in 2 cases. Fourteen patients recovered without sequelae, and only a 2-year-old girl had minimal impairment in fine motor skills at discharge.

Conclusions

All children presenting acute neurological features during influenza season should be evaluated for influenza-associated CNS complications even if the respiratory involvement is mild. Absence of underlying diseases or other risk factors are not protective factors against CNS influenza-associated complications. The lack of CSF pleocytosis does not exclude CNS involvement. Children under 2 years of age are at higher risk of requiring intensive care support.

The Spectrum and Burden of Influenza-Associated Neurological Disease in Children: Combined Encephalitis and Influenza Sentinel Site Surveillance From Australia, 2013-2015

Background

There are few longitudinal studies of seasonal influenza-associated neurological disease (IAND) and none from the Southern Hemisphere.

Methods

We extracted prospectively acquired Australian surveillance data from 2 studies nested within the Paediatric Active Enhanced Disease Surveillance (PAEDS) network: the Influenza Complications Alert Network (FluCAN) study and the Australian Childhood Encephalitis (ACE) study between 2013 and 2015. We described the clinical features and severity of IAND in children, including influenza-associated encephalitis/encephalopathy (IAE). We calculated the proportion of hospitalized influenza that is associated with IAND and IAE, and incidence of IAE.

Results

Over 3 influenza seasons, we identified 54 cases of IAND at 2 tertiary children's hospitals from Australia that accounted for 7.6% of hospitalized influenza. These included 10 cases of IAE (1.4% hospitalized influenza). The mean annual incidence of IAE among Australian children (aged ≤14 years) was 2.8 per 1000000. The spectrum of IAND was broad and included IAE (n = 10) including distinct acute encephalopathy syndromes, simple febrile seizures (n = 14), other seizures (n = 16), acute ataxia (n = 4), and other subacute syndromes (transverse myelitis [n = 1], opsoclonus myoclonus [n = 1]). Two-thirds of children with IAND were aged ≤4 years; less than half had preexisting neurological disease or other risk factors for severe influenza. IAE caused death or neurological morbidity in half of cases.

Conclusions

Seasonal influenza is an important cause of acute neurological disease in Australian children. The spectrum of seasonal IAND appears similar to that described during the 2009 H1N1 pandemic. IAE is associated with high morbidity and mortality.

Vision Loss Caused by Retinal and Lateral Geniculate Nucleus Infarction in H1N1 Influenza

A 13-year-old girl developed encephalopathy and severe bilateral vision loss to the level of light perception within 24 hours of having fever and myalgias heralding H1N1 influenza A. Ophthalmoscopy demonstrated findings of confluent ischemic retinopathy. Brain MRI disclosed lateral geniculate body signal abnormalities indicative of hemorrhagic infarction. Despite aggressive treatment with intravenous corticosteroids, intravenous immunoglobulin, and plasmapheresis, vision did not substantially improve. This case demonstrates that H1N1 can cause simultaneous retinal and lateral geniculate body infarctions, a combination of findings not previously described in any condition. We postulate an immunologic response to the virus marked by occlusive damage to arteriolar endothelium.

A review of the evidence to support influenza vaccine introduction in countries and areas of WHO's Western Pacific Region

Background

Immunization against influenza is considered an essential public health intervention to control both seasonal epidemics and pandemic influenza. According to the World Health Organization (WHO), there are five key policy and three key programmatic issues that decision-makers should consider before introducing a vaccine. These are (a) public health priority, (b) disease burden, (c) efficacy, quality and safety of the vaccine, (d) other inventions, (e) economic and financial issues, (f) vaccine presentation, (g) supply availability and (h) programmatic strength. We analyzed the body of evidence currently available on these eight issues in the WHO Western Pacific Region.

Methodology/Principal Findings

Studies indexed in PubMed and published in English between 1 January 2000 and 31 December 2010 from the 37 countries and areas of the Western Pacific Region were screened for keywords pertaining to the five policy and three programmatic issues. Studies were grouped according to country income level and vaccine target group. There were 133 articles that met the selection criteria, with most (90%) coming from high-income countries. Disease burden (n = 34), vaccine efficacy, quality and safety (n = 27) and public health priority (n = 27) were most frequently addressed by studies conducted in the Region. Many studies assessed influenza vaccine policy and programmatic issues in the general population (42%), in the elderly (24%) and in children (17%). Few studies (2%) addressed the eight issues relating to pregnant women.

Conclusions/Significance

The evidence for vaccine introduction in countries and areas in this Region remains limited, particularly in low- and middle-income countries that do not currently have influenza vaccination programmes. Surveillance activities and specialized studies can be used to assess the eight issues including disease burden among vaccine target groups and the cost-effectiveness of influenza vaccine. Multi-country studies should be considered to maximize resource utilization for cross-cutting issues such as vaccine presentation and other inventions.

Mass Vaccination of Schoolchildren against Influenza and Its Impact on the Influenza-Associated Mortality Rate among Children in Japan

BACKGROUND

Influenza control based on mass vaccination of schoolchildren was implemented in Japan in the 1960s and was associated with a decrease in the overall mortality rate. The program was discontinued in 1994. The discontinuation was followed by a seasonal increase in the mortality rate. Lately, young children and elderly persons have been receiving influenza vaccines. The purpose of this study was to investigate changes in influenza-related mortality among young children before and after discontinuation of mass vaccination of schoolchildren.

METHODS

We calculated the monthly all-cause mortality rates during 1972-2003 and the pneumonia and influenza (P&I) mortality rates during 1972-1999 for young children (age, 1-4 years). We estimated the excess mortality rates attributable to influenza by computing the baseline annual mortality rate as a centered, 3-year moving average of the number of deaths reported during the 2 preceding and the following Decembers.

RESULTS

Prominent winter peaks in monthly all-cause mortality rates among young children occurred in the 1990s. They coincided with the winter peaks in monthly P&I mortality rates among young children and were very similar to the winter peaks observed among elderly persons. The number of excess deaths of young children was estimated to be 783 in the 11 winter seasons from 1990 to 2000, whereas no winter peaks in the number of deaths were seen after 2000.

CONCLUSIONS

It is likely that discontinuation of mass vaccination of schoolchildren was responsible for the increase in influenza-associated deaths among young children in the 1990s. The recent increase in influenza vaccinations among young children, together with the routine therapeutic use of neuraminidase inhibitors, has led to a decrease in the influenza-associated mortality rate.