Critical illness with AH1N1v influenza in pregnancy: a comparison of two population-based cohorts

An evaluation of strategies to achieve greater than 90% coverage of maternal influenza and pertussis vaccines including an economic evaluation

Background

Maternal immunisation is an essential public health intervention aimed at improving the health outcomes for pregnant women and providing protection to the newborn. Despite international recommendations, safety and efficacy data for the intervention, and often a fully funded program, uptake of vaccines in pregnancy remain suboptimal. One possible explanation for this includes limited access to vaccination services at the point of antenatal care. The aim of this study is to evaluate the change in vaccine coverage among pregnant women following implementation of a modified model of delivery aimed at improving access at the point of antenatal care, including an economic evaluation.

Methods

This prospective multi-centre study, using action research design, across six maternity services in Victoria, Australia, evaluated the implementation of a co-designed vaccine delivery model (either a pharmacy led model, midwife led model or primary care led model) supported by provider education. The main outcome measure was influenza and pertussis vaccine uptake during pregnancy and the incremental cost of the new model (compared to existing models) and the cost-effectiveness of the new model at each participating health service.

Results

Influenza vaccine coverage in 2019 increased between 50 and 196% from baseline. All services reduced their average cost per immunisation under the new platforms due to efficiencies achieved in the delivery of maternal immunisations. This cost saving ranged from $9 to $71.

Conclusion

Our study demonstrated that there is no ‘one size fits all’ model of vaccine delivery. Future successful strategies to improve maternal vaccine coverage at other maternity services should be site specific, multifaceted, targeted at the existing barriers to maternal vaccine uptake, and heavily involve local stakeholders in the design and implementation of these strategies. The cost-effectiveness analysis indicates that an increase in maternal influenza immunisation uptake can be achieved at a relatively modest cost through amendment of maternal immunisation platforms.

Safety, Immunogenicity, Efficacy and Effectiveness of Inactivated Influenza Vaccines in Healthy Pregnant Women and Children Under 5 Years: An Evidence-Based Clinical Review

Annual influenza vaccination is often recommended for pregnant women and young children to reduce the risk of severe influenza. However, most studies investigating the safety, immunogenicity, and efficacy or effectiveness of influenza vaccines are conducted in healthy adults. In this evidence-based clinical review, we provide an update on the safety profile, immunogenicity, and efficacy/effectiveness of inactivated influenza vaccines (IIVs) in healthy pregnant women and children <5 years old. Six electronic databases were searched until May 27, 2021. We identified 3,731 articles, of which 93 met the eligibility criteria and were included. The IIVs were generally well tolerated in pregnant women and young children, with low frequencies of adverse events following IIV administration; however, continuous vaccine safety monitoring systems are necessary to detect rare adverse events. IIVs generated good antibody responses, and the seroprotection rates after IIVs were moderate to high in pregnant women (range = 65%-96%) and young children (range = 50%-100%), varying between the different influenza types/subtypes and seasons. Studies show vaccine efficacy/effectiveness values of 50%-70% in pregnant women and 20%-90% in young children against lab-confirmed influenza, although the efficacy/effectiveness depended on the study design, host factors, vaccine type, manufacturing practices, and the antigenic match/mismatch between the influenza vaccine strains and the circulating strains. Current evidence suggests that the benefits of IIVs far outweigh the potential risks and that IIVs should be recommended for pregnant women and young children.

The historical aspects of vaccination in pregnancy

As we live through the history-making pandemic of coronavirus disease 2019 (COVID-19), it is timely to consider the lessons that history has taught us about vaccine-preventable disease in pregnancy. Vaccinations have earned an established place in pregnancy care to prevent communicable disease in the mother, fetus and newborn. The improvements in maternal and perinatal outcome have been achieved through the evolution and application of new knowledge in many areas. These include recognition of the unique pathogenic consequences of diseases in pregnancy; improved understanding of the maternal immune system and its interplay with the fetus; optimizing safe vaccine development; ensuring pregnant women are included in appropriately designed trials of efficacy, and public health engagement to optimize uptake. As the world eagerly awaits an effective vaccine for COVID 19, these lessons of history help signpost the way, to ensure the potential of vaccinations to reduce morbidity for pregnant women and their newborns is fully realized.

Cohort profile: China respiratory illness surveillance among pregnant women (CRISP), 2015-2018

PURPOSE

We established the China Respiratory Illness Surveillance among Pregnant women (CRISP) to conduct active surveillance for influenza-associated respiratory illness during pregnancy in China from 2015 to 2018. Among annual cohorts of pregnant women, we assess the incidence of acute respiratory illness (ARI), influenza-like illness (ILI), laboratory-confirmed influenza virus infection and the seroconversion proportion during the winter influenza season. We also plan to examine the effect of influenza virus infection on adverse pregnancy, delivery and infant health outcomes with cumulative data from the three annual cohorts.

PARTICIPANTS

Cohort nurses enrol pregnant women in different trimesters of pregnancy from prenatal care facilities in Suzhou, Jiangsu Province, eastern China. Pregnant women who plan to deliver in the study facilities are eligible. Pregnant women who are seeking care for anything other than routine prenatal care, such as confirmation of low progesterone and threatened miscarriage, are excluded. At enrolment, study nurses collect baseline information on demographics, education-level attained, underlying medical conditions, seasonal influenza vaccination receipt, risk factors for influenza infection, gravidity and parity and contact information. For each participant, cohort nurses conduct twice weekly follow-up contacts, one phone call and one WeChat message (free instant messaging), from the time of enrolment until delivery or termination of pregnancy. During follow-up, study nurses ask about symptoms, timing and characteristics of ARI, healthcare-seeking behaviour and medications taken for participants reporting respiratory illness since the last contact. In addition, we collect combined nasal and throat swabs for identified ARI to test for influenza viruses. We collect paired sera before and after the influenza season. Active respiratory illness surveillance and seroinfection data during pregnancy of participants are linked to their medical record and the Suzhou Maternal Child Information System for detailed information on clinical treatment for respiratory illness, pregnancy, delivery and infant health outcomes.

FINDINGS TO DATE

In 2015-2016, of 4915 pregnant women approached, 192 (4%) refused to participate, 91 (2%) were ineligible because they did not plan to deliver in one of the study hospitals or because their visit was for anything other than routine prenatal care and 4632 (94%) were enrolled, 46% during their first trimester of pregnancy (range 5-12 weeks), 48% during the second trimester (range 13-27 weeks) and 6% during the third trimester (range 28-37 weeks). The median age of the enrollees was 27 years (range 16-45) and two (0.04%, 95% CI 0.01% to 0.17%) reported influenza vaccination in the previous 12 months before pregnancy, while zero reported influenza vaccination in the previous 12 months during pregnancy. During the observation time of 648 518 person-days, 1355 ARI episodes were identified. Among 1127 swabs collected (for 83% of all ARIs), 68 (6%) tested positive for influenza virus, for a laboratory-confirmed influenza incidence of 0.31 (95% CI 0.25 to 0.40) per 100 person-months during pregnancy in the study cohort.

FUTURE PLANS

Results will be used to describe influenza disease burden in this population to model potential numbers of influenza illnesses averted if influenza vaccination coverage were increased and to support enhanced influenza prevention and control strategies among pregnant women in China. We also plan to enrol and follow three cohorts of pregnant women over three influenza seasons during 2015-2018 which will allow an analysis of the effect of influenza virus infection during pregnancy on adverse pregnancy, delivery and infant outcomes.

Incidence of influenza virus infection among pregnant women: a systematic review

BACKGROUND

The World Health Organization (WHO) considers pregnant women to be a risk group for severe influenza disease. We conducted a systematic review to evaluate influenza disease incidence in pregnant women in order to inform estimates of influenza vaccine impact for low-resource countries.

METHODS

We performed electronic literature searches, targeting studies on the following outcomes in pregnant women: attack rate, hospitalization rate, intensive care unit admission rate, mortality rate, and disability-adjusted life years lost. Only original studies published in peer-reviewed journals that had laboratory confirmation for influenza virus infection and included population-based incidence rates with denominator data were included. We summarized study characteristics in descriptive tables and outcome-specific Forest plots. We generated summary incidence rates using random effects models and assessed statistical heterogeneity by visual examination of Forest plots, and by χ 2 and I2 tests.

RESULTS

We identified 1543 articles, of which nine articles met the study inclusion criteria. Five were case series, three were cohort studies, and one was a randomized controlled trial. Eight studies were from high-income countries, and one was from an upper middle-income country. Six studies reported results for pandemic influenza, and three reported seasonal influenza. Statistical heterogeneity was high for all outcomes, and methodologies and duration of surveillance varied considerably among studies; therefore, we did not perform meta-analyses.

CONCLUSIONS

Study quality was very low according to GRADE criteria. More data on influenza disease incidence in pregnant women, particularly in low- and middle-income countries and for seasonal influenza disease, are needed to inform public health decision-making.

Influenza virus infection in pregnancy: a review

BACKGROUND

Influenza virus infection is very common and a significant cause of morbidity and mortality in specific populations like pregnant women. Following the 2009 pandemic, several reports on the effects of influenza virus infection on maternal health and pregnancy outcome have been published. Also the safety and efficacy of antiviral treatment and vaccination of pregnant women have been studied. In this review, we have analyzed and summarized these data.

OBJECTIVE

To provide information on the influence of influenza virus infection during pregnancy on maternal health and pregnancy outcome and on the effect of treatment and vaccination.

DATA SOURCES

We have searched Medline, Embase and the Cochrane Library. We used influenza, influenz*, pregnancy and pregnan* as search terms.

STUDY SELECTION

In total, 294 reports were reviewed and judged according to the STROBE guidelines or CONSORT statement. In all, 100 studies, published between 1961 and 2015, were included.

RESULTS

Compared to the general population, pregnant women are more often hospitalized and admitted to an intensive care unit due to influenza virus infection. For hospitalized patients, increased rates of preterm birth and fetal/neonatal death are reported. Early treatment with oseltamivir is associated with a reduced risk of severe disease. Vaccination of pregnant women is safe and reduces maternal and neonatal morbidity.

CONCLUSIONS

There is level 2b evidence that maternal health and pregnancy outcome can be severely affected by influenza virus infection. Antiviral treatment may diminish these effects and vaccination protects pregnant women and neonates from infection (level of evidence 2b and 1b, respectively).

[Influenza and pregnancy]

Influenza is a respiratory disease caused by influenza viruses. The virus is responsible for pandemics by emergence of new viral strains, then for seasonal flu by antigenic drift. Seasonal flu is more frequent and severe in pregnant women, with increased risk of pneumonia and increased risk of hospitalization (but no increased death reported). Pandemic flu is more severe in pregnant women, with increased risk of pneumonia and increased mortality. Influenza vaccination is recommended for all women who are or will be pregnant (in any trimester) during influenza season. After closed contact with a flu case or in case of symptoms compatible with flu, early oseltamivir-based treatment (prophylactic in the first situation, curative in the latter one) is recommended, at any term of pregnancy. The occurrence of flu symptoms in a pregnant woman requires medical evaluation to confirm the diagnosis or identify any alternative infection requiring appropriate therapy like listeriosis, chorioamniotitis, pyelonephritis or viral primo-infection.

[The pregnant traveller]

Pregnancy is a physiological situation that requires specific and careful preparation before travel. Malaria, dengue fever and viral hepatitis E are more severe in pregnancy and at higher risk of adverse obstetrical outcome. Medical and obstetrical contra-indications to travel should be listed during pre-travel evaluation. Vaccine indications are the same as in the general population, and must be discussed after a rigorous benefit-risk analysis. Pregnant women should avoid or delay travel in areas of high malarial chloroquino-resistance.

Impact of H1N1 on socially disadvantaged populations: summary of a systematic review

BACKGROUND

Previous reviews found that the H1N1 pandemic was associated with a large proportion of hospitalizations, severe illness, workplace absenteeism, and high costs. However, the burden among socially disadvantaged groups of the population is unclear. This is a summary of a previously published systematic review commissioned by the World Health Organization on the burden of H1N1 pandemic (influenza A/Mexico/2009 (H1N1)) among socially disadvantaged populations.

METHODS

MEDLINE and EMBASE were searched to identify studies reporting hospitalization, severe illness, and mortality attributable to the 2009 H1N1 pandemic among socially disadvantaged populations, including ethnic minorities and low-income or lower-middle-income economy countries (LIC/LMIC). SAS and Review Manager were used to conduct random effects meta-analysis.

RESULTS

Forty-eight cohort studies and 14 companion reports including 44 777 patients were included after screening 787 citations and 164 full-text articles. Twelve of the included studies provided data on LIC/LMIC, including one study from Guatemala, two from Morocco, one from Pakistan, and eight from India, plus four companion reports. The rest provided data on ethnic minorities living in high-income economy countries (HIC). Significantly more hospitalizations were observed among ethnic minorities versus nonethnic minorities in two North American studies [1313 patients, odds ratio (OR) 2·26 (95% confidence interval: 1·53-3·32)]. Among hospitalized patients in HIC, statistically significant differences in intensive care unit admissions (n = 8 studies, 15 352 patients, OR 0·84 [0·69-1·02]) and deaths (n = 6 studies, 14 757 patients, OR 0·85 [95% CI: 0·73-1·01]) were not observed.

CONCLUSION

We found significantly more hospitalizations among ethnic minorities versus nonethnic minorities in North America, yet no differences in intensive care unit admissions or deaths among H1N1-infected hospitalized patients were observed in North America and Australia. Our results suggest a similar burden of H1N1 between ethnic minorities and nonethnic minorities living in HIC.

Maternal and neonatal outcomes among pregnant women with 2009 pandemic influenza A(H1N1) illness in Florida, 2009-2010: a population-based cohort study

Introduction

Pregnant women have been identified as a high risk group for severe illness with 2009 pandemic influenza A(H1N1) virus infection (pH1N1). Obesity has also been identified as a risk factor for severe illness, though this has not been thoroughly assessed among pregnant women. The objectives of this study were to provide risk estimates for adverse maternal and neonatal outcomes associated with pH1N1 illness during pregnancy and to assess the role of obesity in these outcomes.

Methods

We established a retrospective population-based cohort of all live births occurring in Florida during the first 15 months of the pandemic. Illness with pH1N1 during pregnancy was ascertained through record linkage with the Florida state notifiable disease surveillance database. Data from the birth record, including pre-pregnancy body mass index, were analyzed to assess risk of adverse outcomes associated with pH1N1 illness.

Results

A total of 194 women were identified through surveillance with pH1N1 illness during pregnancy. Children born to women with pH1N1 illness during pregnancy were at increased risk for low birth weight [OR (95%CI): 1.78 (1.11-2.860)], premature birth [2.21 (1.47-3.330)], and infant death [4.46 (1.80-11.00)], after adjusting for other factors. Women with pH1N1 illness during pregnancy were at increased risk for severe outcomes including admission to an intensive care unit. Obesity was an observed risk factor, both for the more severe pH1N1 illness detected through surveillance, and for severe maternal outcomes.

Conclusions

Case-patients in this analysis likely represent the most severely ill subset of all women infected with pH1N1 during pregnancy, limiting the generalizability of these findings to more severely ill patients rather than influenza infection in general. Nevertheless, these results suggest that more severe pH1N1 illness during pregnancy is associated with adverse neonatal outcomes and that pregnant women should continue to be targeted for appropriate prophylaxis and early treatment.

Determinants of 2009 A/H1N1 influenza vaccination among pregnant women in Hong Kong

During the 2009–2010 A/H1N1 influenza pandemic, pregnant women infected with the virus experienced excess morbidity and mortality when compared with other groups. Once a vaccine was available, pregnant women were a priority group for vaccination. Only a few studies have reported on the uptake of 2009 A/H1N1 influenza vaccine among pregnant women during the pandemic and none were from Asia. The purpose of this study was to examine factors associated with 2009 A/H1N1 influenza vaccine uptake among pregnant women in Hong Kong. Using a multi-center, cross-sectional design, we recruited 549 postpartum women from four post-natal wards in Hong Kong over a 4-month period during the second wave of the A/H1N1 influenza pandemic in the winter and spring of 2010. Only 6.2% (n = 34) of participants had received the 2009 A/H1N1 influenza vaccine and 4.9% (n = 27) had received the seasonal influenza vaccine. The most common reasons for not receiving the 2009 A/H1N1 vaccine were fear of causing harm to themselves or their fetus. A high knowledge level (OR = 19.06; 95% CI 5.55, 65.48), more positive attitudes (OR = 3.52; 95% CI 1.37, 9.07), and having a family member who had the 2009 A/H1N1 influenza vaccine (OR = 7.69; 95% CI 2.92, 20.19) were independently and positively associated with vaccination. Study results show an unacceptably low uptake of the pandemic A/H1N1 influenza vaccine among pregnant women in Hong Kong. Interventions to increase influenza vaccine knowledge and uptake among this group should be a priority for future pandemic planning and seasonal vaccination campaigns.

The Australasian Maternity Outcomes Surveillance System: an evaluation of stakeholder engagement, usefulness, simplicity, acceptability, data quality and stability

BACKGROUND

The Australasian Maternity Outcomes Surveillance System (AMOSS) conducts active, prospective surveillance of severe maternal conditions in Australia and New Zealand (ANZ). AMOSS captures greater than 96% of all births, and utilises an online, active case-based negative reporting system.

AIM

To evaluate AMOSS using the United States Centres for Disease Control (MMWR 2001; 50 (RR13): 1-35.) surveillance system evaluation framework.

METHODS

Data were gathered using multiple methods, including an anonymous online survey administered to 353 AMOSS data collectors, in addition to review of case data received during 2009-2011, documented records of project board and advisory group meeting minutes, publications, annual reports and the AMOSS database.

RESULTS

AMOSS is a research system characterised by its simplicity and efficiency. The socio-demographic, risk factor and severe morbidity clinical data collected on rare conditions are not duplicated in other routine data systems. AMOSS is functioning well and has sustained buy-in from clinicians, stakeholders and consumers and a high level of acceptability to data collectors in ANZ maternity units.

CONCLUSIONS

AMOSS is the only existing national system of surveillance for rare and severe maternal conditions in ANZ and therefore serves an important function, utilising data collected from reliable sources, in an effective, efficient and timely way.

Effectiveness of an influenza A (H1N1) 2009 monovalent vaccine among Japanese pregnant women: a prospective observational study assessing antibody efficacy

In order to estimate the effectiveness of an influenza A (H1N1) 2009 monovalent vaccine among pregnant women, we prospectively observed 135 Japanese pregnant women who received an influenza A (H1N1) 2009 monovalent vaccine during November 2009. We calculated an index of "antibody efficacy", in which the medical visits for respiratory illnesses were compared between those with and without post-vaccination hemagglutination inhibition (HI) titer ≥1:40. The product of antibody efficacy and achievement rate is theoretically equivalent to the vaccine effectiveness. Among all subjects, an inverse but non-significant relationship during the epidemic period was observed between post-vaccination HI titer ≥1:40 and medical visits for respiratory illnesses. After stratification by trimester at recruitment, a significant inverse association during the epidemic period was found among subjects in the first or second trimester (antibody efficacy: 91%, vaccine effectiveness: 79%). The influenza A (H1N1) 2009 monovalent vaccine administered in the first or second trimester reduced medical visits for respiratory illnesses among Japanese pregnant women.

Impact of H1N1 on socially disadvantaged populations: systematic review

BACKGROUND

The burden of H1N1 among socially disadvantaged populations is unclear. We aimed to synthesize hospitalization, severe illness, and mortality data associated with pandemic A/H1N1/2009 among socially disadvantaged populations.

METHODS/PRINCIPAL FINDINGS

Studies were identified through searching MEDLINE, EMBASE, scanning reference lists, and contacting experts. Studies reporting hospitalization, severe illness, and mortality attributable to laboratory-confirmed 2009 H1N1 pandemic among socially disadvantaged populations (e.g., ethnic minorities, low-income or lower-middle-income economy countries [LIC/LMIC]) were included. Two independent reviewers conducted screening, data abstraction, and quality appraisal (Newcastle Ottawa Scale). Random effects meta-analysis was conducted using SAS and Review Manager.

CONCLUSIONS/SIGNIFICANCE

Sixty-two studies including 44,777 patients were included after screening 787 citations and 164 full-text articles. The prevalence of hospitalization for H1N1 ranged from 17-87% in high-income economy countries (HIC) and 11-45% in LIC/LMIC. Of those hospitalized, the prevalence of intensive care unit (ICU) admission and mortality was 6-76% and 1-25% in HIC; and 30% and 8-15%, in LIC/LMIC, respectively. There were significantly more hospitalizations among ethnic minorities versus non-ethnic minorities in two studies conducted in North America (1,313 patients, OR 2.26 [95% CI: 1.53-3.32]). There were no differences in ICU admissions (n = 8 studies, 15,352 patients, OR 0.84 [0.69-1.02]) or deaths (n = 6 studies, 14,757 patients, OR 0.85 [95% CI: 0.73-1.01]) among hospitalized patients in HIC. Sub-group analysis indicated that the meta-analysis results were not likely affected by confounding. Overall, the prevalence of hospitalization, severe illness, and mortality due to H1N1 was high for ethnic minorities in HIC and individuals from LIC/LMIC. However, our results suggest that there were little differences in the proportion of hospitalization, severe illness, and mortality between ethnic minorities and non-ethnic minorities living in HIC.

Complications of the 2009 influenza A/H1N1 pandemic in pregnant women in The Netherlands: a national cohort study

The 2009 influenza A/H1N1 pandemic caused an increase in complications in pregnant women. To be well prepared for a next pandemic, we investigated the obstetric and maternal complications of this pandemic. In our national cohort of 59 pregnant women who were admitted to the hospital, no major complications apart from preterm birth and admission to the neonatal intensive care unit were observed. Although the small size of this study precludes us drawing any definitive conclusions, comparing our results with those in other countries suggests that the influenza A/H1N1 pandemic had a relatively benign course in pregnant women in The Netherlands.