Roles for Pathogen Interference in Influenza Vaccination, with Implications to Vaccine Effectiveness (VE) and Attribution of Influenza Deaths

Pathogen interference is the ability of one pathogen to alter the course and clinical outcomes of infection by another. With up to 3000 species of human pathogens the potential combinations are vast. These combinations operate within further immune complexity induced by infection with multiple persistent pathogens, and by the role which the human microbiome plays in maintaining health, immune function, and resistance to infection. All the above are further complicated by malnutrition in children and the elderly. Influenza vaccination offers a measure of protection for elderly individuals subsequently infected with influenza. However, all vaccines induce both specific and non-specific effects. The specific effects involve stimulation of humoral and cellular immunity, while the nonspecific effects are far more nuanced including changes in gene expression patterns and production of small RNAs which contribute to pathogen interference. Little is known about the outcomes of vaccinated elderly not subsequently infected with influenza but infected with multiple other non-influenza winter pathogens. In this review we propose that in certain years the specific antigen mix in the seasonal influenza vaccine inadvertently increases the risk of infection from other non-influenza pathogens. The possibility that vaccination could upset the pathogen balance, and that the timing of vaccination relative to the pathogen balance was critical to success, was proposed in 2010 but was seemingly ignored. Persons vaccinated early in the winter are more likely to experience higher pathogen interference. Implications to the estimation of vaccine effectiveness and influenza deaths are discussed.

Seasonal Influenza Vaccination Coverage Trends Among Adult Populations, U.S., 2010-2016

INTRODUCTION

Influenza is a major cause of morbidity and mortality among adults. The most effective strategy for preventing influenza is annual vaccination. However, vaccination coverage has been suboptimal among adult populations. The purpose of this study is to assess trends in influenza vaccination among adult populations.

METHODS

Data from the 2010-2016 National Health Interview Survey were analyzed in 2018 to estimate vaccination coverage during the 2010-2011 through 2015-2016 seasons. Trends of vaccination in recent years were assessed. Vaccination coverage by race/ethnicity within each group was examined. Multivariable logistic regression and predictive marginal models were conducted to identify factors associated with vaccination, and interactions between race/ethnicity and other demographic and access-to-care characteristics were assessed.

RESULTS

Vaccination coverage among adults aged ≥18 years increased from 38.3% in the 2010-2011 season to 43.4% in the 2015-2016 season, with an average increase of 1.3 percentage points annually. From the 2010-2011 through 2015-2016 seasons, coverage was stable for adults aged ≥65 years and changed by -0.1 to 9.9 percentage points for all other examined subgroups. Coverage in 2015-2016 was 70.4% for adults aged ≥65 years, 46.4% for those aged 50-64 years, and 32.3% for those aged 18-49 years; 47.9% for people aged 18-64 years with high-risk conditions; 64.8% for healthcare personnel; and 50.3% for pregnant women. Among adults aged ≥18 years for the 2015-2016 season, coverage was significantly lower among non-Hispanic blacks and Hispanics compared with non-Hispanic whites.

CONCLUSIONS

Overall, influenza vaccination coverage among adults aged ≥18 years increased during 2010-2016, but it remained below the national target of 70%. Vaccination coverage varied by age, risk status, race/ethnicity, healthcare personnel, and pregnancy status. Targeted efforts are needed to improve coverage and reduce disparities.

Association of provider recommendation and offer and influenza vaccination among adults aged ≥18 years - United States

BACKGROUND

Influenza vaccination has been recommended for all persons aged ≥6 months since 2010.

METHODS

Data from the 2016 National Internet Flu Survey were analyzed to assess provider vaccination recommendations and early influenza vaccination during the 2016-17 season among adults aged ≥18 years. Predictive marginals from a multivariable logistic regression model were used to identify factors independently associated with early vaccine uptake by provider vaccination recommendation status.

RESULTS

Overall, 24.0% visited a provider who both recommended and offered influenza vaccination, 9.0% visited a provider who only recommended but did not offer, 25.1% visited a provider who neither recommended nor offered, and 41.9% did not visit a doctor from July 1 through date of interview. Adults who reported that a provider both recommended and offered vaccine had significantly higher vaccination coverage (66.6%) compared with those who reported that a provider only recommended but did not offer (48.4%), those who neither received recommendation nor offer (32.0%), and those who did not visit a doctor during the vaccination period (28.8%). Results of multivariable logistic regression indicated that having received a provider recommendation, with or without an offer for vaccination, was significantly associated with higher vaccination coverage after controlling for demographic and access-to-care factors.

CONCLUSIONS

Provider recommendation was significantly associated with influenza vaccination. However, overall, 67.0% of adults did not visit a doctor during the vaccination period or did visit a doctor but did not receive a provider recommendation. Evidence-based strategies such as client reminder/recall, standing orders, provider reminders, or health systems interventions in combination should be undertaken to improve provider recommendation and influenza vaccination coverage. Other factors significantly associated with a higher level of influenza vaccination included age ≥50 years, being Hispanic, having a college or higher education, having a usual place for medical care, and having public health insurance.

Knowledge of influenza vaccination recommendation and early vaccination uptake during the 2015-16 season among adults aged ≥18years - United States

BACKGROUND

Since 2010, the Advisory Committee on Immunization Practices (ACIP) has recommended that all persons aged ≥6months receive annual influenza vaccination.

METHODS

We analyzed data from the 2015 National Internet Flu Survey (NIFS), to assess knowledge and awareness of the influenza vaccination recommendation and early influenza vaccination coverage during the 2015-16 season among adults. Predictive marginals from a multivariable logistic regression model were used to identify factors independently associated with adults' knowledge and awareness of the vaccination recommendation and early vaccine uptake during the 2015-16 influenza season.

RESULTS

Among the 3301 respondents aged ≥18years, 19.6% indicated knowing that influenza vaccination is recommended for all persons aged ≥6months. Of respondents, 62.3% indicated awareness that there was a recommendation for influenza vaccination, but did not indicate correct knowledge of the recommended age group. Overall, 39.9% of adults aged ≥18years reported having an influenza vaccination. Age 65years and older, being female, having a college or higher education, not being in work force, having annual household income ≥$75,000, reporting having received an influenza vaccination early in the 2015-16 season, having children aged ≤17years in the household, and having high-risk conditions were independently associated with a higher correct knowledge of the influenza vaccination recommendation.

CONCLUSIONS

Approximately 1 in 5 had correct knowledge of the recommendation that all persons aged ≥6months should receive an influenza vaccination annually, with some socio-economic groups being even less aware. Clinic based education in combination with strategies known to increase uptake of recommended vaccines, such as patient reminder/recall systems and other healthcare system-based interventions are needed to improve vaccination, which could also improve awareness.

Effect of previous and current vaccination against influenza A(H1N1)pdm09, A(H3N2), and B during the post-pandemic period 2010-2016 in Spain

BACKGROUND

Recent studies suggest that the protective effect of the current influenza vaccine could be influenced by vaccination in previous seasons. We estimated the combined effect of the previous and current influenza vaccines from the 2010-2011 season to the 2015-2016 season in Spain.

METHODS

We performed a test-negative case-control study in patients ≥9 years old. We estimated the influenza vaccine effectiveness (IVE) against influenza A(H1N1)pdm09, A(H3N2), and B virus.

RESULTS

We included 1206 influenza A(H1N1)pdm09 cases, 1358 A(H3N2) cases and 1079 B cases. IVE against A(H1N1)pdm09 virus in the pooled-season analysis was 53% (95% Confidence Interval (CI): 21% to 72%) for those vaccinated only in the current season and 50% (95%CI: 23% to 68%) for those vaccinated in the both current and previous seasons. Against the influenza A(H3N2) virus, IVE was 17% (95%CI: -43% to 52%) for those vaccinated only in the current season and 3% (95%CI: -33% to 28%) for those vaccinated in both seasons. Regarding influenza B, we obtained similar IVEs for those vaccinated only in the current and those vaccinated in both seasons: 57% (95%CI: 12% to 79%) and 56% (95%CI: 36% to 70%), respectively.

CONCLUSION

Our results suggested no interference between the previous and current influenza vaccines against A(H1N1)pdm09 and B viruses, but a possible negative interference against A(H3N2) virus.

Concordance of interim and final estimates of influenza vaccine effectiveness: a systematic review

The World Health Organization's Global Influenza Surveillance and Response System meets twice a year to generate a recommendation for the composition of the seasonal influenza vaccine. Interim vaccine effectiveness (VE) estimates provide a preliminary indication of influenza vaccine performance during the season and may be useful for decision making. We reviewed 17 pairs of studies reporting 33 pairs of interim and final estimates using the test-negative design to evaluate whether interim estimates can reliably predict final estimates. We examined features of the study design that may be correlated with interim estimates being substantially different from their final estimates and identified differences related to change in study period and concomitant changes in sample size, proportion vaccinated and proportion of cases. An absolute difference of no more than 10% between interim and final estimates was found for 18 of 33 reported pairs of estimates, including six of 12 pairs reporting VE against any influenza, six of 10 for influenza A(H1N1)pdm09, four of seven for influenza A(H3N2) and two of four for influenza B. While we identified inconsistencies in the methods, the similarities between interim and final estimates support the utility of generating and disseminating preliminary estimates of VE while virus circulation is ongoing.

Guillain-Barré syndrome following the 2009 pandemic monovalent and seasonal trivalent influenza vaccination campaigns in Spain from 2009 to 2011: outcomes from active surveillance by a neurologist network, and records from a country-wide hospital discharge database

Background

Studies have shown a slight excess risk in Guillain-Barré syndrome (GBS) incidence associated with A(H1N1)pdm09 vaccination campaign and seasonal trivalent influenza vaccine immunisations in 2009–2010. We aimed to assess the incidence of GBS as a potential adverse effect of A(H1N1)pdm09 vaccination.

Methods

A neurologist-led network, active at the neurology departments of ten general hospitals serving an adult population of 4.68 million, conducted GBS surveillance in Spain in 2009–2011. The network, established in 1996, carried out a retrospective and a prospective study to estimate monthly alarm thresholds in GBS incidence and tested them in 1998–1999 in a pilot study. Such incidence thresholds additionally to observation of GBS cases with immunisation antecedent in the 42 days prior to clinical onset were taken as alarm signals for 2009–2011, since November 2009 onwards. For purpose of surveillance, in 2009 we updated both the available centres and the populations served by the network. We also did a retrospective countrywide review of hospital-discharged patients having ICD-9-CM code 357.0 (acute infective polyneuritis) as their principal diagnosis from January 2009 to December 2011.

Results

Among 141 confirmed of 148 notified cases of GBS or Miller-Fisher syndrome, Brighton 1–2 criteria in 96 %, not a single patient was identified with clinical onset during the 42-day time interval following A(H1N1)pdm09 vaccination. In contrast, seven cases were seen during a similar period after seasonal campaigns. Monthly incidence figures did not, however, exceed the upper 95 % CI limit of expected incidence. A retrospective countrywide review of the registry of hospital-discharged patients having ICD-9-CM code 357.0 (acute infective polyneuritis) as their principal diagnosis did not suggest higher admission rates in critical months across the period December 2009-February 2010.

Conclusions

Despite limited power and underlying reporting bias in 2010–2011, an increase in GBS incidence over background GBS, associated with A(H1N1)pdm09 monovalent or trivalent influenza immunisations, appears unlikely.

Estimating influenza vaccine effectiveness in Spain using sentinel surveillance data

We aimed to estimate influenza vaccine effectiveness (VE) against laboratory-confirmed influenza during three influenza seasons (2010/11 to 2012/2013) in Spain using surveillance data and to compare the results with data obtained by the cycEVA study, the Spanish component of the Influenza Monitoring Vaccine Effectiveness (I-MOVE) network. We used the test-negative case–control design, with data from the Spanish Influenza Sentinel Surveillance System (SISS) or from the cycEVA study. Cases were laboratory-confirmed influenza patients with the predominant influenza virus of each season, and controls were those testing negative for any influenza virus. We calculated the overall and age-specific adjusted VE. Although the number of patients recorded in the SISS was three times higher than that in the cycEVA study, the quality of information for important variables, i.e. vaccination status and laboratory results, was high in both studies. Overall, the SISS and cycEVA influenza VE estimates were largely similar during the study period. For elderly patients (> 59 years), the SISS estimates were slightly lower than those of cycEVA, and estimates for children (0–14 years) were higher using SISS in two of the three seasons studied. Enhancing the SISS by collecting the date of influenza vaccination and reducing the percentage of patients with incomplete information would optimise the system to provide reliable annual influenza VE estimates to guide influenza vaccination policies.

Influenza vaccination coverage and effectiveness in young children in Thailand, 2011-2013

BACKGROUND

Since 2009, Thailand has recommended influenza vaccine for children aged 6 months through 2 years, but no estimates of influenza vaccine coverage or effectiveness are available for this target group.

METHODS

During August 2011-May 2013, high-risk and healthy children aged ≤36 months were enrolled in a 2-year prospective cohort study. Parents were contacted weekly about acute respiratory illness (ARI) in their child. Ill children had combined nasal and throat swabs tested for influenza viruses by real-time reverse transcription-polymerase chain reaction. Influenza vaccination status was verified with vaccination cards. The Cox proportional hazards approach was used to estimate hazard ratios. Vaccine effectiveness (VE) was estimated as 100% x (1-hazard ratio).

RESULTS

During 2011-2013, 968 children were enrolled (median age, 10·3 months); 948 (97·9%) had a vaccination record and were included. Of these, 394 (41·6%) had ≥1 medical conditions. Vaccination coverage for the 2011-2012 and 2012-2013 seasons was 29·3% (93/317) and 30·0% (197/656), respectively. In 2011-2012, there were 213 ARI episodes, of which 10 (4·6%) were influenza positive (2·3 per 1000 vaccinated and 3·8 per 1000 unvaccinated child-weeks). The VE was 55% (95% confidence interval [CI], -72, 88). In 2012-2013, there were 846 ARIs, of which 52 (6·2%) were influenza positive (1·8 per 1000 vaccinated and 4·5 per 1000 unvaccinated child-weeks). The VE was 64% (CI, 13%, 85%).

CONCLUSION

Influenza vaccination coverage among young children in Thailand was low, although vaccination was moderately effective. Continued efforts are needed to increase influenza vaccination coverage and evaluate VE among young children in Thailand.

Effectiveness of seasonal influenza vaccinations against laboratory-confirmed influenza-associated infections among Singapore military personnel in 2010-2013

BACKGROUND

Limited information is available about seasonal influenza vaccine effectiveness (VE) in tropical communities.

OBJECTIVES

Virus subtype-specific VE was determined for all military service personnel in the recruit camp and three other non-recruit camp in Singapore's Armed Forces from 1 June 2009 to 30 June 2012.

METHODS

Consenting servicemen underwent nasal washes, which were tested with RT-PCR and subtyped. The test positive case and test negative control design was used to estimate the VE. To estimate the overall effect of the programme on new recruits, we used an ecological time series approach.

RESULTS

A total of 7016 consultations were collected. The crude estimates for the VE of the triavalent vaccine against both influenza A(H1N1)pdm09 and influenza B were 84% (95% CI 78-88%, 79-86%, respectively). Vaccine efficacy against influenza A(H3N2) was markedly lower (VE 33%, 95% CI -4% to 57%). An estimated 70% (RR = 0.30; 95% CI 0.11-0.84), 39% (RR = 0.61;0.25-1.43) and 75% (RR = 0.25; 95% CI 0.11-0.50) reduction in the risk of influenza A(H1N1)pdm09, influenza A(H3N2) and influenza B infections, respectively, in the recruit camp during the post-vaccination period compared with during the pre-vaccination period was observed.

CONCLUSIONS

Overall, the blanket influenza vaccine programme in Singapore's Armed Forces has had a moderate to high degree of protection against influenza A(H1N1)pdm09 and influenza B, but not against influenza A(H3N2). Blanket influenza vaccination is recommended for all military personnel.

Influenza vaccine effectiveness in Spain 2013/14: subtype-specific early estimates using the cycEVA study

Adjusted early estimates of the 2013/14 influenza vaccine effectiveness (VE) in Spain for all age groups was 35% (95% CI: -9 to 62), 33% (95% CI: -33 to 67) and 28% (95% CI: -33 to 61) against any influenza virus type, A(H1N1)pdm09 and A(H3N2) viruses, respectively. For the population targeted for vaccination, the adjusted VE was 44% (95% CI: -11 to 72), 36% (95% CI: -64 to 75) and 42% (95% CI: -29 to 74), respectively. These preliminary results in Spain suggest a suboptimal protective effect of the vaccine against circulating influenza viruses.

Effectiveness of influenza vaccine against laboratory-confirmed influenza, in the late 2011-2012 season in Spain, among population targeted for vaccination

BACKGROUND

In Spain, the influenza vaccine effectiveness (VE) was estimated in the last three seasons using the observational study cycEVA conducted in the frame of the existing Spanish Influenza Sentinel Surveillance System. The objective of the study was to estimate influenza vaccine effectiveness (VE) against medically attended, laboratory-confirmed influenza-like illness (ILI) among the target groups for vaccination in Spain in the 2011-2012 season. We also studied influenza VE in the early (weeks 52/2011-7/2012) and late (weeks 8-14/2012) phases of the epidemic and according to time since vaccination.

METHODS

Medically attended patients with ILI were systematically swabbed to collect information on exposure, laboratory outcome and confounding factors. Patients belonging to target groups for vaccination and who were swabbed <8 days after symptom onset were included. Cases tested positive for influenza and controls tested negative for any influenza virus. To examine the effect of a late season, analyses were performed according to the phase of the season and according to the time between vaccination and symptoms onset.

RESULTS

The overall adjusted influenza VE against A(H3N2) was 45% (95% CI, 0-69). The estimated influenza VE was 52% (95% CI, -3 to 78), 40% (95% CI, -40 to 74) and 22% (95% CI, -135 to 74) at 3.5 months, 3.5-4 months, and >4 months, respectively, since vaccination. A decrease in VE with time since vaccination was only observed in individuals aged ≥ 65 years. Regarding the phase of the season, decreasing point estimates were only observed in the early phase, whereas very low or null estimates were obtained in the late phase for the shortest time interval.

CONCLUSIONS

The 2011-2012 influenza vaccine showed a low-to-moderate protective effect against medically attended, laboratory-confirmed influenza in the target groups for vaccination, in a late season and with a limited match between the vaccine and circulating strains. The suggested decrease in influenza VE with time since vaccination was mostly observed in the elderly population. The decreasing protective effect of the vaccine in the late part of the season could be related to waning vaccine protection because no viral changes were identified throughout the season.

2011-12 seasonal influenza vaccines effectiveness against confirmed A(H3N2) influenza hospitalisation: pooled analysis from a European network of hospitals. A pilot study

BACKGROUND

Influenza vaccination strategies aim at protecting high-risk population from severe outcomes. Estimating the effectiveness of seasonal vaccines against influenza related hospitalisation is important to guide these strategies. Large sample size is needed to have precise estimate of influenza vaccine effectiveness (IVE) against severe outcomes. We assessed the feasibility of measuring seasonal IVE against hospitalisation with laboratory confirmed influenza through a network of 21 hospitals in the European Union.

METHODS

We conducted a multicentre study in France (seven hospitals), Italy (one hospital), and Navarra (four hospitals) and Valencia (nine hospitals) regions in Spain. All ≥18 years hospitalised patients presenting an influenza-like illness within seven days were swabbed. Cases were patients RT-PCR positive for influenza A (H3N2); controls were patients negative for any influenza virus. Using logistic regression with study site as a fixed effect we calculated IVE adjusted for potential confounders. We restricted the analyses to those swabbed within four days.

RESULTS

We included, 375 A(H3N2) cases and 770 controls. The overall adjusted IVE was 24.9% (95%CI-1.8;44.6). Among the target group for vaccination (N = 1058) the adjusted IVE was 28.8% (95%CI:2.8;47.9); it was respectively 36.8% (95%CI:-48.8; 73.1), 42.6% (95%CI:-16.5;71.7), 17.8%(95%CI:-40.8; 52.1) and 37.5% (95%CI:-22.8;68.2) in the age groups 18-64, 65-74, 75-84 and more than 84 years.

DISCUSSION

Estimation of IVE based on the pooling of data obtained through a European network of hospitals was feasible. Our results suggest a low IVE against hospitalised confirmed influenza in 2011-12. The low IVE may be explained by a poor immune response in the high-risk population, imperfect match between vaccine and circulating strain or waning immunity due to a late season. Increased sample size within this network would allow more precise estimates and stratification of the IVE by time since vaccination and vaccine types or brands.

Surveillance and vaccine effectiveness of an influenza epidemic predominated by vaccine-mismatched influenza B/Yamagata-lineage viruses in Taiwan, 2011-12 season

Introduction

The 2011−12 trivalent influenza vaccine contains a strain of influenza B/Victoria-lineage viruses. Despite free provision of influenza vaccine among target populations, an epidemic predominated by influenza B/Yamagata-lineage viruses occurred during the 2011−12 season in Taiwan. We characterized this vaccine-mismatched epidemic and estimated influenza vaccine effectiveness (VE).

Methods

Influenza activity was monitored through sentinel viral surveillance, emergency department (ED) and outpatient influenza-like illness (ILI) syndromic surveillance, and case-based surveillance of influenza with complications and deaths. VE against laboratory-confirmed influenza was evaluated through a case-control study on ILI patients enrolled into sentinel viral surveillance. Logistic regression was used to estimate VE adjusted for confounding factors.

Results

During July 2011−June 2012, influenza B accounted for 2,382 (72.5%) of 3,285 influenza-positive respiratory specimens. Of 329 influenza B viral isolates with antigen characterization, 287 (87.2%) were B/Yamagata-lineage viruses. Proportions of ED and outpatient visits being ILI-related increased from November 2011 to January 2012. Of 1,704 confirmed cases of influenza with complications, including 154 (9.0%) deaths, influenza B accounted for 1,034 (60.7%) of the confirmed cases and 103 (66.9%) of the deaths. Reporting rates of confirmed influenza with complications and deaths were 73.5 and 6.6 per 1,000,000, respectively, highest among those aged ≥65 years, 50−64 years, 3−6 years, and 0−2 years. Adjusted VE was −31% (95% CI: −80, 4) against all influenza, 54% (95% CI: 3, 78) against influenza A, and −66% (95% CI: −132, −18) against influenza B.

Conclusions

This influenza epidemic in Taiwan was predominated by B/Yamagata-lineage viruses unprotected by the 2011−12 trivalent vaccine. The morbidity and mortality of this vaccine-mismatched epidemic warrants careful consideration of introducing a quadrivalent influenza vaccine that includes strains of both B lineages.