2015/16 I‐MOVE/I‐MOVE+ multicentre case‐control study in Europe: Moderate vaccine effectiveness estimates against influenza A(H1N1)pdm09 and low estimates against lineage‐mismatched influenza B among children

Background

During the 2015/16 influenza season in Europe, the cocirculating influenza viruses were A(H1N1)pdm09 and B/Victoria, which was antigenically distinct from the B/Yamagata component in the trivalent influenza vaccine.

Methods

We used the test‐negative design in a multicentre case‐control study in twelve European countries to measure 2015/16 influenza vaccine effectiveness (VE) against medically attended influenza‐like illness (ILI) laboratory‐confirmed as influenza. General practitioners swabbed a systematic sample of consulting ILI patients and a random sample of influenza‐positive swabs was sequenced. We calculated adjusted VE against influenza A(H1N1)pdm09, A(H1N1)pdm09 genetic group 6B.1 and influenza B overall and by age group.

Results

We included 11 430 ILI patients, of which 2272 were influenza A(H1N1)pdm09 and 2901 were influenza B cases. Overall VE against influenza A(H1N1)pdm09 was 32.9% (95% CI: 15.5‐46.7). Among those aged 0‐14, 15‐64 and ≥65 years, VE against A(H1N1)pdm09 was 31.9% (95% CI: ? 32.3 to 65.0), 41.4% (95% CI: 20.5‐56.7) and 13.2% (95% CI: ? 38.0 to 45.3), respectively. Overall VE against influenza A(H1N1)pdm09 genetic group 6B.1 was 32.8% (95% CI: ? 4.1 to 56.7). Among those aged 0‐14, 15‐64 and ≥65 years, VE against influenza B was ? 47.6% (95% CI: ? 124.9 to 3.1), 27.3% (95% CI: ? 4.6 to 49.4) and 9.3% (95% CI: ? 44.1 to 42.9), respectively.

Conclusions

Vaccine effectiveness (VE) against influenza A(H1N1)pdm09 and its genetic group 6B.1 was moderate in children and adults, and low among individuals ≥65 years. Vaccine effectiveness (VE) against influenza B was low and heterogeneous among age groups. More information on effects of previous vaccination and previous infection is needed to understand the VE results against influenza B in the context of a mismatched vaccine.

     

Assessing the reporting quality of influenza outbreaks in the community

Background

High‐quality reporting of outbreak characteristics is fundamental to understand the behaviour of various strains of influenza virus and the impact of outbreak management strategies. However, few studies have systematically evaluated the quality of outbreak reporting.

Objectives

To conduct a systematic analysis and assessment for reporting quality of influenza outbreaks based on a modified version of the STROBE statement, and to examine characteristics associated with reporting quality.

Methods

A literature search was conducted across 3 online databases (PubMed, Web of Science, MEDLINE) for reports of influenza outbreaks (pandemic H1N1, avian, seasonal). The quality of reports meeting our eligibility criteria was assessed using the Modified STROBE criteria and assigned a score of 30. Mean differences (MD) and 95% confidence intervals (CI) were reported for comparisons of study characteristics.

Results

Sixty‐four outbreak reports were available for analyses. The average Modified STROBE score was 20/30. Peer‐reviewed articles were associated with a better quality of reporting (MD 2.79, 95% CI 0.79‐4.78). Likewise, reports from authors affiliated with public health agencies were associated with better quality than those from academic institutions (MD 1.65, 95% CI?0.27‐3.56).

Conclusions

The development of explicit reporting guidelines specifically geared towards reporting of outbreak investigations proved to be useful. Providing information on patient characteristics, investigation details in introduction and results, as well as addressing limitations that could have biased the findings, were frequently missing in the published reports.

     

The safety and efficacy of quadrivalent live attenuated influenza vaccine in Japanese children aged 2‐18 years: Results of two phase 3 studies

Background

Quadrivalent live attenuated influenza vaccine (Q/LAIV) has not been assessed in Japanese children.

Objectives

Evaluate safety and efficacy of Q/LAIV in Japanese children.

Patients/methods

Two phase 3 studies were conducted in the 2014‐2015 influenza season. Study 1 was an open‐label, uncontrolled single arm, multicenter study of Q/LAIV safety in subjects aged 2‐6 years. Study 2 was a randomized, double‐blind, placebo‐controlled multicenter study of Q/LAIV safety and efficacy; subjects aged 7‐18 years were randomized 2:1 to receive Q/LAIV or placebo. Primary efficacy endpoint was laboratory‐confirmed symptomatic influenza infection caused by vaccine‐matched strains; secondary endpoint evaluated efficacy against all strains regardless of match. Both studies reported solicited symptoms, adverse events (AEs), and serious AEs.

Results

In Study 1, 100 subjects received Q/LAIV. In Study 2, 1301 subjects received Q/LAIV (n = 868) or placebo (n = 433). Treatment‐emergent AEs occurred in 42% of subjects in Study 1, and in 24.3% of subjects in the Q/LAIV arm and in 25.9% of subjects in the placebo arm in Study 2. In Study 2, a single infection by a vaccine‐matched strain was reported in the placebo arm, resulting in a vaccine efficacy estimate of 100% (95% CI: ?1875.3, 100.0); efficacy for all strains regardless of match to the vaccine was 27.5% (95% CI: 7.4, 43.0).

Conclusions

Quadrivalent live attenuated influenza vaccine did not meet its primary efficacy endpoint as only a single infection by a vaccine‐matched strain was detected; however, efficacy for the secondary endpoint, all strains regardless of match, was achieved. Q/LAIV was generally well tolerated in the Japanese pediatric population.

     

Migratory birds in southern Brazil are a source of multiple avian influenza virus subtypes

Background

There is insufficient knowledge about the relation of avian influenza virus (AIV) to migratory birds in South America. Accordingly, we studied samples obtained over a 4‐year period (2009‐2012) from wild birds at a major wintering site in southern Brazil.

Methods

We obtained 1212 oropharyngeal/cloacal samples from wild birds at Lagoa do Peixe National Park and screened them for influenza A virus by RT‐PCR amplification of the matrix gene. Virus isolates were subjected to genomic sequencing and antigenic characterization.

Results

Forty‐eight samples of 1212 (3.96%) contained detectable influenza virus RNA. Partial viral sequences were obtained from 12 of these samples, showing the presence of H2N2 (1), H6Nx (1), H6N1 (8), H9N2 (1), and H12N5 (1) viruses. As H6 viruses predominated, we generated complete genomes from all 9 H6 viruses. Phylogenetic analyses showed that they were most similar to viruses of South American lineage. The H6N1 viruses caused no disease signs in infected ferrets and, despite genetic differences, were antigenically similar to North American isolates.

Conclusions

Lagoa do Peixe National Park is a source of multiple AIV subtypes, with the levels of influenza virus in birds being highest at the end of their wintering period in this region. H6N1 viruses were the predominant subtype identified. These viruses were more similar to viruses of South American lineage than to those of North American lineage.

     

Improving the representativeness of influenza viruses shared within the WHO Global Influenza Surveillance and Response System

Background

Sharing influenza viruses within the WHO Global Influenza Surveillance and Response System is crucial for monitoring evolution of influenza viruses.

Objectives

Analysis of timeliness and geographic representativeness of viruses shared by National Influenza Centres (NICs) in the WHO European Region with the London WHO Collaborating Centre for Reference and Research on Influenza for the Northern Hemisphere''s 2010–2011 and 2011–2012 influenza seasons.

Materials and methods

Data from NICs on influenza‐positive specimens shared with WHO CC London for the above‐mentioned influenza seasons were analyzed for timeliness of sharing with respect to the February deadline (31 January) for inclusion in the WHO consultations on the composition of influenza virus vaccines for the Northern Hemisphere and geographic representativeness.

Results

The 2010–2011 and 2011–2012 seasons were different in terms of the seasonal pattern, the timing of the epidemic, and the dominant virus. Consistent patterns of virus sharing across the seasons were observed. Approximately half the viruses collected before the deadline were not shared within the deadline; the average delay between date of specimen collection and shipment receipt was 3 and 1·5 months for the first and second season, respectively.

Conclusion

A baseline was provided for future work on enhancement of specimen sharing in the WHO European Region and improving the vaccine virus selection process. Greater insight into virus selection criteria applied by countries and the causes of delays in shipment are needed to understand the representativeness of viruses shared and to assess the importance of this for vaccine strain selection.     

Distribution of influenza and other acute respiratory viruses during the first year after the 2009–2010 influenza pandemic in the English‐ and Dutch‐speaking Caribbean countries

Background

Limited specimen collection and testing for influenza occurred in the English and Dutch‐speaking Caribbean countries prior to the 2009/2010 influenza pandemic. Caribbean Epidemiology Centre (CAREC) member countries rapidly mobilized to collect specimens during the pandemic and a vast majority of confirmed cases during the pandemic period were influenza A(H1N1)pdm09.

Objectives

To describe the aetiology and distribution of acute respiratory illness (ARI) among laboratory confirmed cases during the first year after the 2009/2010 influenza pandemic in the English‐ and Dutch‐speaking Caribbean.

Results

In total, 774 specimens were tested and 394 (52.7%) cases had positive laboratory confirmation. Respiratory syncytial virus (RSV) (28.4%) and influenza A(H3N2) (23.1%) were most frequently detected. RSV activity peaked in July 2011 while influenza A(H3N2) peaked in October 2010. Influenza was responsible for illness in greater numbers in persons 15–64 years while RSV was seen in primarily in children <5 years and adults >65 years. Other agents confirmed include rhinovirus (12.9%), influenza B (10.9%) and influenza A(H1N1)pdm09 (9.4%).

Conclusions

RSV and influenza A(H3N2) were the most common viruses identified during the first year after the influenza A(H1N1)pdm09 pandemic. Influenza was detected every month with peak activity corresponding to that typically seen in North America (October to March). In order to determine the seasonality of influenza and RSV, laboratory data from subsequent years and increased specimen submission is needed.     

Divergent seasonal patterns of influenza types A and B across latitude gradient in Tropical Asia

Introduction

Influenza circulation in tropics and subtropics reveals a complex seasonal pattern with year‐round circulation in some areas and biannual peaks in others.

Methods

We analyzed influenza surveillance data from nine countries around southern and southeastern Asia spanning latitudinal gradient from equatorial to temperate zones to further characterize influenza type‐specific seasonality in the region. We calculated proportion of positives by month out of positives during that year and adjust for variation in samples tested and positivity in these countries.

Results

Influenza A epidemics were identified between November and March during winters in areas lying above 30°N latitude, during monsoon months of June–November in areas between 10° and 30°N latitude, and no specific seasonality for influenza A virus circulation in areas lying closer to the equator. Influenza B circulation coincided with influenza A circulation in areas lying above 30°N latitude; however, in areas south of 30°N Asia, influenza B circulated year round at 3–8% of annual influenza B positives during most months with less pronounced peaks during post‐monsoon period.

Conclusion

Even though influenza B circulates round the year in most areas of the tropical regions of southern and southeastern Asia, the most appropriate time for influenza vaccination using the most recent WHO recommended vaccine would be prior to the monsoon season conferring protection against influenza A and B peaks.     

A novel approach for preparation of the antisera reagent for potency determination of inactivated H7N9 influenza vaccines

Background

The potency of inactivated influenza vaccines is determined using a single‐radial immunodiffusion (SRID) assay and requires standardized reagents consisting of a Reference Antigen and an influenza strain‐specific antiserum. Timely availability of reagents is a critical step in influenza vaccine production, and the need for backup approaches for reagent preparation is an important component of pandemic preparedness.

Objectives

When novel H7N9 viruses emerged in China in 2013, candidate inactivated H7N9 influenza vaccines were developed for evaluation in clinical trials, and reagents were needed to measure vaccine potency.

Methods

We previously described an alternative approach for generating strain‐specific potency antisera, utilizing modified vaccinia virus Ankara vectors to produce influenza hemagglutinin (HA)‐containing virus‐like particles (VLPs) for immunization. Vector‐produced HA antigen is not dependent upon the success of the traditional bromelain‐digestion and HA purification.

Results

Antiserum for H7N9 vaccines, produced after immunization of sheep with preparations of bromelain‐HA (br‐HA), was not optimal for the SRID assay, and the supply of antiserum was limited. However, antiserum obtained from sheep boosted with VLPs containing H7 HA greatly improved the ring quality in the SRID assay. Importantly, this antiserum worked well with both egg‐ and cell‐derived antigen and was distributed to vaccine manufacturers.

Conclusions

Utilizing a previously developed approach for preparing vaccine potency antiserum, we have addressed a major bottleneck encountered in preparation of H7N9 vaccine reagents. The combination of br‐HA and mammalian VLPs for sequential immunization represents the first use of an alternative approach for producing an influenza vaccine potency antiserum.     

Counting pandemic deaths: comparing reported numbers of deaths from influenza A(H1N1)pdm09 with estimated excess mortality

Background

During the wave 1 of the influenza A(H1N1)pdm09 virus, Norway appeared to be suffering from high mortality rates. However, by the end of the pandemic, it was widely reported that the number of deaths were much lower than previous years.

Objectives

The mortality burden from influenza is often assessed by two different approaches: counting influenza‐certified deaths and estimating the mortality burden using models. The purpose of this study is to compare the number of reported deaths with results from two different models for estimating excess mortality during the pandemic in Norway. Additionally, mortality estimates for the pandemic season are compared with non‐pandemic influenza seasons.

Methods

Numbers on reported influenza A(N1h1)pdm09 deaths are gived by the Cause of Death Registry at Statistics Norway and an ad hoc registry at the Norwegian Institute of Public Health. Overall and Pnemumonia and Influenza certified mortality is modeled using Poission regression, adjusting for levels of reported influenza‐like illness and seasonal and year‐to‐year variation.

Results and conclusions

Modelling results suggest that the excess mortality in older age groups is considerably lower during the pandemic than non‐pandemic seasons, but there are indications of an excess beyond what was reported during the pandemic. This highlights the benefits of both methods and the importance of explaining where these numbers come from.     

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.     

Seroprevalence of antibody to influenza A(H1N1)pdm09 attributed to vaccination or infection,before and after the second (2010) pandemic wave in Australia

Objectives

Historical records of influenza pandemics demonstrate variability in incidence and severity between waves. The influenza A(H1N1)pdm09 pandemic was the first in which many countries implemented strain-specific vaccination to mitigate subsequent seasons. Serosurveys provide opportunity to examine the constraining influence of antibody on population disease experience.

Design

Changes in the proportion of adults seropositive to influenza A(H1N1)pdm09over the 2009/10 (summer) interepidemic period and 2010 (winter) influenza season were measured to determine whether there was a temporal relationship with vaccine distribution and influenza activity, respectively.

Setting

Australia.

Sample

Plasma samples were collected from healthy blood donors from seven cities at the end of the first wave (November 2009), and before (March/April 2010) and after (November 2010) the subsequent influenza season.

Main outcome measures

Haemagglutination inhibition (HI) assays were performed to assess reactivity of plasma against A(H1N1)pdm09, and the proportion seropositive (HI titre ≥ 40) compared over time, by age group and location.

Results

Between the 2009 and 2010 influenza seasons, the seropositive proportion rose from 22% to 43%, an increase observed across all ages and sites. Brisbane alone recorded a significant rise in seropositivity over the 2010 influenza season – from a baseline of 35% to 53%. The seropositive proportion elsewhere was ≥40% pre-season, and did not rise over winter.

Conclusions

A vaccine-associated increase in seropositive proportion preceding the influenza season correlated with low levels of disease activity in winter 2010. These observations support the role of immunisation in mitigating the ‘second wave’ of A(H1N1)pdm09, with timing critical to ensure sustained herd protection.     

Influenza H1N1pdm‐specific maternal antibodies offer limited protection against wild‐type virus replication and influence influenza vaccination in ferrets

Objective

The objective was to study passively acquired influenza H1N1 pandemic (H1N1pdm) maternal antibody kinetics and its impact on subsequent influenza infection and vaccination in ferrets during an outbreak of the H1N1pdm.

Design and main outcome measures

Infectivity of the H1N1pdm in the respiratory tract of ferrets was compared with the previous seasonal A/South Dakota/6/2007 (SD07, H1N1). Influenza-specific antibodies were quantitated and antibody-mediated protection against the homologous and heterologous H1N1 virus challenge infection was determined.

Results

H1N1pdm virus was approximately 10 times more infectious than SD07 in ferrets, replicated to higher viral titers in the upper respiratory tract and shed for a longer duration. Influenza-specific antibodies after natural infection persisted much longer in the circulation than passively acquired maternal antibodies. The protection conferred by the maternal antibodies was limited to the homologous virus strain and was ineffective against SD07 and H3N2 virus. Serum antibodies from maternal transmission or passive transfer interfered with homologous vaccine strain-mediated antibody responses in the ferret. A booster immunization was required to elicit a high level of antibody.

Conclusions

The findings support the rationale for a prime and boost immunization strategy in young children in whom maternal antibodies are present.     

Emergence of H3N2pM‐like and novel reassortant H3N1 swine viruses possessing segments derived from the A (H1N1)pdm09 influenza virus,Korea

Background

Human‐to‐swine transmission of the pandemic H1N1 2009 [A(H1N1)pdm09] virus in pig populations resulted in reassortment events with endemic swine influenza viruses worldwide.

Objective

We investigated whether A(H1N1)pdm09‐derived reassortant viruses are present in South Korea and sought to determine the pathogenic potential of the novel swine viruses.

Methods

Pig lung tissues were collected from commercially slaughtered pigs. Isolated swine influenza viruses were genetically analyzed and characterized in vitro and in vivo.

Results

We identified reassortant H3N2 (H3N2pM‐like) and H3N1 swine viruses containing A(H1N1)pdm09‐like segments in Korean pigs that are genetically closely related to strains recently detected in pigs and humans in North America. Although the H3N2pM‐like and novel H3N1 reassortants demonstrated efficient replication in mice and ferrets, all the H3N1 strains exhibited growth advantage over the representative H3N2pM‐like virus in human airway cells. Interestingly, A/swine/Korea/CY02‐07/2012(H3N1) and A/swine/Korea/CY03‐13/2012(H3N1) reassortants were more readily transmitted to respiratory‐droplet‐contact ferrets compared with the H3N2pM‐like (A/swine/Korea/CY02‐10/2012) isolate. Furthermore, serologic evaluation showed poor antigenicity to contemporary reference human seasonal H3N2 vaccine strains.

Conclusions

We report here for the first time the isolation of H3N2pM‐like viruses outside North America and of novel reassortant swine H3N1 viruses with A(H1N1)pdm09‐derived genes. Apart from further complicating the genetic diversity of influenza A viruses circulating in domestic pigs, our data also indicate that these strains could potentially pose threat to public health asserting the need for continuous virus monitoring in these ecologically important hosts.     

Seasonal influenza vaccine effectiveness among children, 2010–2012

Background

The annual differences in the seasonal influenza vaccine and the circulating strains make it necessary to assess influenza vaccine effectiveness (VE) yearly. We assessed the effectiveness of the trivalent inactivated influenza vaccine for the 2010–2011 and 2011–2012 influenza seasons among children in Guangzhou, China.

Methods

We conducted a 1:2 matched case–control study based on date of birth (±7 days), gender, and area of residence. The influenza cases from surveillance sites in Guangzhou were laboratory‐confirmed during the 2010–2012 seasons. The controls were randomly selected from children aged 6–59 months in the Children''s Expanded Programmed Immunization Administrative Computerized System. The influenza vaccination information for both cases and controls was retrieved from this system.

Results

We analyzed the vaccination information for 1255 influenza cases and 2510 matched controls in 2 influenza seasons in Guangzhou, China. We found that the VE for vaccination during the 2010–2011 and 2011–2012 seasons of virus circulation was 73·2% (95% confidence interval (CI), 52·2–85·0%) and 52·9% (95% CI, 42·1–61·7%), respectively. The VE decreased from 68·9% (95% CI, 57·5–77·2%) in the period between January and March to 48·4% (95% CI, 33·8–59·7%) in the period between April and June.

Conclusions

This post‐licensing study of VE found moderate protection against influenza for vaccinated children aged 6–59 months. Although the influenza vaccine strains for the 2010–2011 and the 2011–2012 seasons were the same, our study indicated that annual vaccination is recommended even for those who received the vaccine during the previous season.     

Effect of passive immunization on immunogenicity and protective efficacy of vaccination against a Mexican low‐pathogenic avian H5N2 influenza virus

Background

Despite the use of vaccines, low‐pathogenic (LP) H5N2 influenza viruses have continued to circulate and evolve in chickens in Mexico since 1993, giving rise to multiple genetic variants. Antigenic drift is partially responsible for the failure to control H5N2 influenza by vaccination; the contribution of maternal antibodies to this problem has received less attention.

Methods

We investigated the effect of different antisera on the efficacy of vaccination and whether booster doses of vaccine can impact immune suppression.

Results

While single doses of inactivated oil emulsion vaccine to currently circulating H5N2 influenza viruses provide partial protection from homologous challenge, chickens that receive high‐titer homologous antisera intraperitoneally before vaccination showed effects ranging from added protection to immunosuppression. Post‐infection antisera were less immunosuppressive than antisera obtained from field‐vaccinated chickens. Homologous, post‐infection chicken antisera provided initial protection from virus challenge, but reduced the induction of detectable antibody responses. Homologous antisera from field‐vaccinated chickens were markedly immunosuppressive, annulling the efficacy of the vaccine and leaving the chickens as susceptible to infection as non‐vaccinated birds. Booster doses of vaccine reduced the immunosuppressive effects of the administered sera.

Conclusion

Vaccine efficacy against LP H5N2 in Mexico can be severely reduced by maternal antibodies. Source‐dependent antisera effects offer the possibility of further elucidation of the immunosuppressive components involved.     

Cost‐effectiveness analysis of antiviral treatment in the management of seasonal influenza A: point‐of‐care rapid test versus clinical judgment

Background

A point‐of‐care rapid test (POCRT) may help early and targeted use of antiviral drugs for the management of influenza A infection.

Objective

(i) To determine whether antiviral treatment based on a POCRT for influenza A is cost‐effective and, (ii) to determine the thresholds of key test parameters (sensitivity, specificity and cost) at which a POCRT based‐strategy appears to be cost effective.

Methods

An hybrid « susceptible, infected, recovered (SIR) » compartmental transmission and Markov decision analytic model was used to simulate the cost‐effectiveness of antiviral treatment based on a POCRT for influenza A in the social perspective. Data input parameters used were retrieved from peer‐review published studies and government databases. The outcome considered was the incremental cost per life‐year saved for one seasonal influenza season.

Results

In the base‐case analysis, the antiviral treatment based on POCRT saves 2 lives/100 000 person‐years and costs $7600 less than the empirical antiviral treatment based on clinical judgment alone, which demonstrates that the POCRT‐based strategy is dominant. In one and two way‐sensitivity analyses, results were sensitive to the POCRT accuracy and cost, to the vaccination coverage as well as to the prevalence of influenza A. In probabilistic sensitivity analyses, the POCRT strategy is cost‐effective in 66% of cases, for a commonly accepted threshold of $50 000 per life‐year saved.

Conclusion

The influenza antiviral treatment based on POCRT could be cost‐effective in specific conditions of performance, price and disease prevalence.     

Effectiveness of influenza vaccination in preventing influenza in primary care,Navarre, Spain, 2021/22

Compared with individuals unvaccinated in the current and three previous influenza seasons, in 2021/22, influenza vaccine effectiveness at primary care level was 37% (95% CI: 16 to 52) for current season vaccination, regardless of previous doses, and 35% (95% CI: −3 to 45) for only previous seasons vaccination. Against influenza A(H3N2), estimates were 39% (95% CI: 16 to 55) and 24% (95% CI: −8 to 47) suggesting moderate effectiveness of current season vaccination and possible remaining effect of prior vaccinations.     

Timing of influenza epidemics and vaccines in the American tropics, 2002–2008, 2011–2014

Background

Influenza‐associated illness results in increased morbidity and mortality in the Americas. These effects can be mitigated with an appropriately chosen and timed influenza vaccination campaign. To provide guidance in choosing the most suitable vaccine formulation and timing of administration, it is necessary to understand the timing of influenza seasonal epidemics.

Objectives

Our main objective was to determine whether influenza occurs in seasonal patterns in the American tropics and when these patterns occurred.

Methods

Publicly available, monthly seasonal influenza data from the Pan American Health Organization and WHO, from countries in the American tropics, were obtained during 2002–2008 and 2011–2014 (excluding unseasonal pandemic activity during 2009–2010). For each country, we calculated the monthly proportion of samples that tested positive for influenza. We applied the monthly proportion data to a logistic regression model for each country.

Results

We analyzed 2002–2008 and 2011–2014 influenza surveillance data from the American tropics and identified 13 (81%) of 16 countries with influenza epidemics that, on average, started during May and lasted 4 months.

Conclusions

The majority of countries in the American tropics have seasonal epidemics that start in May. Officials in these countries should consider the impact of vaccinating persons during April with the Southern Hemisphere formulation.     

Assessment of potential public health impact of a quadrivalent inactivated influenza vaccine in Thailand

Background

Each year, an influenza B strain representing only one influenza B lineage is included in the trivalent inactivated influenza vaccine (IIV3); a mismatch between the selected lineage and circulating viruses can result in suboptimal vaccine effectiveness. We modeled the added potential public health impact of a quadrivalent inactivated influenza vaccine (IIV4) that includes strains from both influenza B lineages compared to IIV3 on influenza‐associated morbidity and mortality in Thailand.

Methods

Using data on the incidence of influenza‐associated hospitalizations and deaths, vaccine effectiveness, and vaccine coverage from the 2007–2012 influenza seasons in Thailand, we estimated rates of influenza‐associated outcomes that might be averted using IIV4 instead of IIV3. We then applied these rates to national population estimates to calculate averted illnesses, hospitalizations, and deaths for each season. We assumed that the influenza B lineage included in IIV3 would provide a relative vaccine effectiveness of 75% against the other B lineage.

Results

Compared to use of IIV3, use of IIV4 might have led to an additional reduction ranging from 0·4 to 14·3 influenza‐associated illnesses per 100 000 population/year, <0·1 to 0·5 hospitalizations per 100 000/year, and <0·1 to 0·4 deaths per 1000/year. Based on extrapolation to national population estimates, replacement of IIV3 with IIV4 might have averted an additional 267–9784 influenza‐associated illnesses, 9–320 hospitalizations, and 0–3 deaths.

Conclusion

Compared to use of IIV3, IIV4 has the potential to further reduce the burden of influenza‐associated morbidity and mortality in Thailand.