Preventing influenza in younger children

Influenza vaccination coverage in pediatric population in Italy: an analysis of recent trends

BACKGROUND

Influenza is a major cause of morbidity, mortality and exacerbation of extant chronic disease worldwide. Influenza vaccination is thus fundamental to reduce the burden of disease. In this study, we describe the trend of influenza vaccination coverage in the seasons 2010/11-2020/21 among children aged < 2, 2-4 and 5-8 in Italy.

METHODS

We analyzed the trend of influenza vaccination coverage in the pediatric population in Italy from the 2010/11 to the 2020/21 season at national and regional level and observed the incidence of influenza-like illness (ILI) in the pediatric population between 2010/11 and 2020/21.

RESULTS

In the period 2010/11-2019/20 the highest value of coverage (4.5%) was reached in the age group 2-4 and 5-8 (season 2010/11 and 2011/12, respectively), while the lowest belonged to the < 2 group (1.1% in the season 2015/16). In the season 2020/2021 all the age groups reported a substantial increase of coverage compared with the previous season. The highest value (19.0%) was reported in the age group 2-4, followed by the group 5-8 and <  2 (13.1 and 9.2%, respectively). Considering the rates of annual ILI cases, the highest value for the 0-4 age group was 18.5% in the 2011/12 season; for the 5-14 age group, the highest value was 27.7% in the 2010/11 season.

CONCLUSIONS

Over the past 11 years pediatric influenza vaccination coverage in Italy has been low, with relevant differences across regions and seasons, albeit a general increase in coverage has been observed in the 2020/21 season. Universal influenza vaccination for children should be considered as a priority for the high incidence in this age group. Further research is needed to improve knowledge and comparability of coverage rates, and to identify the best practices for organizational models of delivery which can support the improvement of trends, the acceptability and accessibility by parents and awareness in stakeholders and decision makers.

Pertussis and influenza immunisation coverage of pregnant women in New Zealand

BACKGROUND

Immunisation is an important public health policy and measuring coverage is imperative to identify gaps and monitor trends. New Zealand (NZ), like many countries, does not routinely publish coverage of immunisations given during pregnancy. Therefore, this study examined pregnancy immunisation coverage of all pregnant NZ women between 2013 and 2018, and what factors affected uptake.

METHODS

A retrospective cohort study of pregnant women who delivered between 2013 and 2018 was undertaken using administrative datasets. Maternity and immunisation data were linked to determine coverage of pertussis and influenza vaccinations in pregnancy. Generalised estimating equations were used to estimate the odds of receiving a vaccination during pregnancy.

RESULTS

From 2013 to 2018 data were available for 323,622 pregnant women, of whom 21.7% received maternal influenza immunisations and 25.7% maternal pertussis immunisations. Coverage for both vaccines increased over time, pertussis increased from 10.2% to 43.6% and influenza from 11.2% to 30.8%. The odds of being vaccinated, with either vaccine, during pregnancy increased with increasing age and decreasing deprivation. Compared to NZ European or Other women, Māori and Pacific women had lower odds of receiving a maternal pertussis (OR:0.55, 95% CI: 0.54, 0.57; OR:0.60, 95% CI: 0.58, 0.62, respectively) and influenza (OR: 0.69, 95% CI: 0.67, 0.71; OR:0.90, 95% CI: 0.87, 0.94, respectively) immunisations during pregnancy. Women were also more likely to be vaccinated against pertussis if they received antenatal care from a General Practitioner or Obstetrician compared to a Midwife. A similar pattern was seen for influenza vaccination.

CONCLUSION

Gaps in maternal coverage for pertussis and influenza exist and work is needed to reduce immunisation inequities.

Influenza vaccines: Evaluation of the safety profile

The safety of vaccines is a critical factor in maintaining public trust in national vaccination programs. Vaccines are recommended for children, adults and elderly subjects and have to meet higher safety standards, since they are administered to healthy subjects, mainly healthy children. Although vaccines are strictly monitored before authorization, the possibility of adverse events and/or rare adverse events cannot be totally eliminated. Two main types of influenza vaccines are currently available: parenteral inactivated influenza vaccines and intranasal live attenuated vaccines. Both display a good safety profile in adults and children. However, they can cause adverse events and/or rare adverse events, some of which are more prevalent in children, while others with a higher prevalence in adults. The aim of this review is to provide an overview of influenza vaccine safety according to target groups, vaccine types and production methods.

Protection of young children from influenza through universal vaccination

Influenza is a very common disease among infants and young children, with a considerable clinical and socioeconomic impact. A significant number of health authorities presently recommend universal influenza vaccination for the pediatric population, but a large number of European health authorities is still reluctant to include influenza vaccination in their national vaccination programs. The reasons for this reluctance include the fact that the protection offered by the currently available vaccines is considered poor. This review shows that although future research could lead to an increase in the immunogenicity and potential efficacy of influenza vaccines, the available vaccines, even with their limits, assure sufficient protection in most subjects aged ≥ 6 months, thus reducing the total burden of influenza in young children and justifying the recommendation for the universal vaccination of the whole pediatric population. For younger subjects, the vaccination of their mother during pregnancy represents an efficacious strategy.

Consecutive Infections With Influenza A and B Virus in Children During the 2014-2015 Seasonal Influenza Epidemic

In a retrospective analysis of the test results for 647 patients with laboratory-confirmed influenza, we identified 13 children with influenza A virus infection who were subsequently infected with influenza B virus after a mean interval of 50 days. None of these children were considered immunodeficient or had an increased frequency of infections. Our data provide novel information in showing that consecutive infection with influenza A and B viruses can occur during a regular influenza season in immune-competent children and that a preceding influenza A virus infection may not provide cross-protection against influenza B virus infection.

Influenza vaccination in pediatric age

To increase the protective efficacy against influenza in pediatric populations, several attempts to modify the composition or the route of administration of an inactivated influenza vaccine have been made. Adjuvants have been added, vaccines with higher antigen content have been developed and intradermal administration of inactivated influenza vaccine with a variety of devices has been considered. Such attempts to develop universal influenza vaccines will continue to be made. For some time, the knowledge that the licensed influenza vaccines induce strain-specific immunity and may have low efficacy in unexpected outbreaks of new epidemic strains has motivated the development of preparations with broader and longer-lasting protection. Ideally, children would be included early in the evaluation of the efficacy of new vaccines to avoid lengthy delays in making the protection available to this vulnerable population. Moreover, further studies to clarify definitively whether protection of infants <6 months of age can be obtained through vaccination of the pregnant woman have to be performed.

Epidemiological study of influenza B in Shanghai during the 2009-2014 seasons: implications for influenza vaccination strategy

A new quadrivalent influenza vaccine has been available for influenza B, which can pose a significant global health burden. Shanghai has the highest GDP and largest metropolitan population in China. To understand the impact of influenza B in Shanghai in terms of age-related incidence and relative prevalence compared with other subtypes, we conducted this retrospective epidemiological study of influenza B in the 2009-2014 seasons. A total of 71 354 outpatients with influenza-like illness were included, and both lineages of influenza B and subtypes of influenza A were identified using real-time RT-PCR. The antigenic characteristics of influenza B isolates were analysed by sequencing and reciprocal haemagglutinin inhibition assay. On average, 33.45% of influenza strains were influenza B, and 40.20% of strains isolated from children were influenza B. The incidence of influenza B was highest (12.52 per 100 people with influenza-like illness) in children ages 6-17 years and usually peaked in this age group at the early stage of an influenza B epidemic. Overall, both matched and mismatched influenza B strains co-circulated in Shanghai annually, and 44.57% of the circulating influenza B belonged to the opposite lineage of the vaccine strains. We concluded that influenza B has caused a substantial impact in Shanghai and that school-aged children play a key role in the transmission of influenza B. Hence, it may be beneficial to prioritize influenza vaccination for school-aged children to mitigate the outbreaks of influenza B.

Effectiveness of trivalent flu vaccine in healthy young children

BACKGROUND

There are few studies evaluating the effectiveness of trivalent influenza vaccination (TIV) in young children, particularly in children <2 years. The Western Australian Influenza Vaccine Effectiveness Study commenced in 2008 to evaluate a program providing TIV to children aged 6 to 59 months.

METHODS

An observational study enrolling children with influenza-like illness presenting to a tertiary pediatric hospital was conducted (2008-2012). Vaccination status was determined by parental questionnaire and confirmed via the national immunization register and/or vaccine providers. Respiratory virus polymerase chain reaction and culture were performed on nasopharyngeal samples. The test-negative design was used to estimate vaccine effectiveness (VE) by using 2 control groups: all influenza test-negative subjects and other-virus-detected (OVD) subjects. Adjusted odds ratios were estimated from models with season, month of disease onset, age, gender, indigenous status, prematurity, and comorbidities as covariates. Subjects enrolled in 2009 were excluded from VE calculations.

RESULTS

Of 2001 children enrolled, influenza was identified in 389 (20.4%) children. Another respiratory virus was identified in 1134 (59.6%) children. Overall, 295 of 1903 (15.5%) children were fully vaccinated and 161 of 1903 (8.4%) children were partially vaccinated. Vaccine uptake was significantly lower in 2010-2012 after increased febrile adverse events observed in 2010. Using test-negative controls, VE was 64.7% (95% confidence interval [CI]: 33.7%-81.2%). No difference in VE was observed with OVD controls (65.8%; 95% CI: 32.1%-82.8%). The VE for children <2 years was 85.8% (95% CI: 37.9%-96.7%).

CONCLUSIONS

This study reveals the effectiveness of TIV in young children over 4 seasons by using test-negative and OVD controls. TIV was effective in children aged <2 years. Despite demonstrated vaccine effectiveness, uptake of TIV remains suboptimal.

Impact of a mixed bacterial lysate (OM-85 BV) on the immunogenicity, safety and tolerability of inactivated influenza vaccine in children with recurrent respiratory tract infection

It is known that the immunogenicity and efficacy of conventional inactivated influenza vaccines (IIVs) are not completely satisfactory in children. The aim of this prospective, randomised, single-blind study was to compare the immune response to, and the effectiveness and safety of, an IIV (Fluarix, GlaxoSmithKline Biologicals, Rixensart, Belgium) administered to 68 children aged 36-59 months affected by recurrent respiratory tract infections (RRTIs) who were vaccinated with (n=33) or without (n=35) the mixed bacterial lysate OM-85 BV (Broncho-vaxom, Vifor Pharma, Geneva, Switzerland). OM-85 BV had no effect on seroconversion or seroprotection rates, geometric mean titres, or dendritic cells, which were not significantly different between the two groups. Moreover, OM-85 BV did not significantly increase the pool of the memory B cells that produce IgG and IgM antibodies against the influenza antigens. However, respiratory morbidity was significantly lower in the children treated with OM-85 BV (p<0.05), thus confirming its positive effect on the incidence of RRTIs. There was no difference in the incidence of adverse events between the two groups. These findings show that the immune response of children to influenza vaccine is not significantly influenced by the administration of OM-85 BV. However, the use of OM-85 before and at the same time as IIV seems to reduce respiratory morbidity, and seems to be safe and well tolerated.

Inactivated and adjuvanted influenza vaccines

Inactivated influenza vaccines are produced every year to fight against the seasonal epidemics of influenza. Despite the nonoptimal coverage, even in subjects at risk like the elderly, pregnant women, etc., these vaccines significantly reduce the burden of mortality and morbidity linked to the influenza infection. Importantly, these vaccines have also contributed to reduce the impact of the last pandemics. Nevertheless, the performance of these vaccines can be improved mainly in those age groups, like children and the elderly, in which their efficacy is suboptimal. The use of adjuvants has proven effective to this scope. Oil-in-water adjuvants like MF59 and AS03 have been licensed and widely used, and shown efficacious in preventing influenza infection in the last pandemic. MF59-adjuvanted inactivated vaccine was more efficacious than non-adjuvanted vaccine in preventing influenza infection in young children and in reducing hospitalization due to the influenza infection in the elderly. Other adjuvants are now at different stages of development and some are being tested in clinical trials. The perspective remains to improve the way inactivated vaccines are prepared and to accelerate their availability, mainly in the case of influenza pandemics, and to enhance their efficacy/effectiveness for a more successful impact at the public health level.