Low response to a monovalent inactivated unadjuvanted influenza A (H1N1) pdm09 vaccine in pediatricians of a general hospital in Japan

Abstract

Immunization of health care personnel (HCP) is critically important to reduce healthcare-associated influenza infections substantially. During 2009–2010, 74% of all HCP at Kitano Hospital, Osaka, Japan, including 94% of pediatricians, received the monovalent unadjuvanted influenza A (H1N1) pdm09 vaccine.

 

We evaluated the vaccine’s immunogenicity. Sixteen pediatricians received 15 μg hemagglutinin antigen subcutaneously. Antibody titer assays were conducted using hemagglutination-inhibition antibody assay on days 0 and 21 and at 5 mo after vaccination. Seroprotection rates, seroconversion rates, and geometric mean titer folds at 21 d were, respectively, 43.8%, 43.8% and 5.4 in all subjects, 70.0%, 70.0% and 8.0 in subjects aged 27–34 y, and 0.0%, 0.0% and 8.0 in subjects aged ≥ 35 y. None of the latter group met the European Medicines Agency criteria.

We hope to adopt intradermal routes and further the development of the influenza vaccine using new technology to improve immunogenicity in Japan.

Keywords: :

• monovalent influenza A (H1N1) pdm09 vaccine
• health care personnel
• pediatricians

Introduction

Influenza vaccination of health care personnel (HCP) is regarded as an important evidence-based public health measure used to mitigate the influenza virus pandemic. In an early stage (July–August) of the 2009 A (H1N1) influenza pandemic, international organizations (WHO, European and US Centers for Disease Control and Prevention––ECDC and CDC) issued evidence-based recommendations for target groups for pandemic vaccination to help standardize national policies. Consistently, HCP were included in the priority groups, although target groups for vaccination differed among European countries.¹ Influenza vaccination coverage remains low,^2-5 and regional disparities persist. The American Academy of Pediatrics has recommended the implementation of a mandatory annual influenza immunization policy for all HCP for the prevention and control of influenza.⁶ Despite the sustained efforts of many organizations to improve influenza immunization rates, influenza coverage among HCP in Western countries remains low. The Ministry of Health, Labour and Welfare (MHLW) in Japan recommended in October 2009 that HCP should receive vaccinations for pandemic influenza (H1N1) 2009. Pediatricians placed high priority on the vaccination program in the hospital because children and young adults were disproportionately affected by pandemic influenza then.^7,8 We experienced an unexpectedly low response to a monovalent influenza A (H1N1) pdm09 vaccine in pediatricians in spite of high vaccination coverage. We also report the current vaccine delivery situation in Japan and highlight some implications for technological innovation for improving immunogenicity of the vaccine.

Subjects and Methods

Participants

In October 2009, to assess front-line HCP receiving the influenza A (H1N1) pdm09 vaccine, we evaluated the immunogenicity of a monovalent influenza A (H1N1) pdm09 vaccine in pediatricians at Kitano Hospital, which plays a central role in community health care as a general hospital in the city of Osaka. The hospital, with integrated pediatric emergency and outpatient departments, has 2,300 pediatric admissions per year, and provides consultation to 30,000 children with common pediatric disorders as well as more complex autoimmune diseases. Such patients are immunocompromised because of malignancies or are at high risk for poor outcomes from influenza. For this study, 16 healthy pediatricians who had not contracted influenza at the time of enrollment received one dose of the assigned vaccine subcutaneously. Before inclusion in the study, which was approved by the Kitano Hospital and the Tazuke Kofukai Medical Research Institute Ethics Committee, they provided written informed consent. This trial was registered with the Ministry of Education, Culture, Sports, Science and Technology, Japan (UMIN000004392). Patients showed signs and symptoms compatible with influenza as assessed using the influenza rapid antigen test: overall sensitivity and specificity were 80% and 93% during the study period, the 2009–2010 H1N1 season.⁹

Vaccine

The monovalent unadjuvanted inactivated split-virion influenza A (H1N1) pdm09 vaccine (Lot. No. SL03B) was produced by the Chemo-Sero Therapeutic Research Institute (Kaketsuken), Kumamoto, Japan. The seed virus used for vaccine production was A/California/7/2009(H1N1) virus, a candidate reassortant vaccine virus recommended by WHO.¹⁰ The vaccine was prepared in embryonated chicken eggs using the same standard techniques and was presented in 10-ml multidose vials with thimerosal added as a preservative. A single 0.5-ml dose included 15 μg of hemagglutinin antigen. The monovalent unadjuvanted inactivated split-virion influenza A (H1N1) pdm09 vaccine was first licensed by MHLW in Japan on 22 October 2009 as a single dose for HCPs as a top priority. Patients with underlying diseases and second doses for children aged 1–9 y were assigned subordinate priority because MHLW sought the vaccination of people at high risk of developing flu-related complications. Consequently, all HCP examined in this study received one dose of vaccine. More than one week after the A (H1N1) influenza vaccine immunization, conventional trivalent inactivated, split influenza vaccines of each of the following three influenza antigens were administered: A/Uruguay/716/2007 (A/H3N2), A/Brisbane/59/2007 (A/H1N1), and B/Brisbane/60/2008.

Immunogenicity

Anti-hemagglutinin (HI) antibody titers against the influenza A (H1N1) pdm09 vaccine were evaluated at enrollment, at 21 d and at 5 mo after vaccination. Immunogenicity was assessed using the European Medicines Agency (EMA) criteria¹¹ as follows: seroprotection rate (percentage of subjects with a post-vaccination titer ≥ 1:40) > 70% for subjects aged 18–60, seroconversion rate (either a post-vaccination titer ≥ 1:40 in subjects with a pre-vaccination titer of < 1:10 or a ≥ 4-fold titer increase in subjects with a pre-vaccination titer of ≥ 1:10) > 40% for subjects aged 18–60, and fold increase in geometric mean titers (GMT) after vaccination > 2.5 for subjects aged 18–60. One criterion must be met for the licensure of seasonal influenza vaccine. All laboratory assays were performed by the Osaka Prefectural Institute of Public Health.

Statistical analysis

Immunogenicity results were described as point estimates for the mean with 95% confidence intervals (CIs). Those intervals, which were calculated based on a binomial distribution, are provided for descriptive statistics. All analyses were conducted using a software package (JMP 8.0.1; SAS Institute Inc.).

Results

Study subjects

During the winter period of 2009–2010, among 1,226 staff, 904 (73.7%) received influenza A (H1N1) pdm09 vaccine, 1,071 (87.4%) received seasonal vaccine and 112 (9.1%) received neither (Table 1). Of 1134 HCP, 831 (73.1%) received the pandemic vaccine, 991 (87.4%) received seasonal vaccine and 104 (9.2%) received neither (Table 1).

Table 1. Characteristics of staff and pandemic influenza A (H1N1) 2009 and Seasonal Influenza vaccination coverage

	Total number of staff	Pandemic A(H1N1)2009 vaccinated subject number	Pandemic A(H1N1)2009 vaccination rate (%)	Seasonal influenza vaccinated subjects	Seasonal influenza vaccination rate (%)
Overall vaccination 2008–2009	1,191	0	0	1,035	86.9
Overall vaccination 2010–2011	1,247	1,072	86.0	1,072	86.0
Overall vaccination 2009–2010	1,226	904	73.7	1,071	87.4
All healthcare professionals	1,134	830	73.2	991	87.4
Physicians (except pediatricians) Pediatricians	232 18	163 17	70.3 94.4	179 17	77.2 94.4
Total number of medical doctors	250	180	72.0	196	78.4
Nurses and nursing assistants	692	494	71.4	625	90.3
Pharmacists	27	22	81.5	22	81.5
Technicians	192	152	79.2	170	88.5
Administrative personnel	92	74	80.4	80	87.0

Ten male and six female pediatricians received influenza A (H1N1) pdm09 vaccines and then seasonal vaccines. The vaccination coverage rate against A (H1N1) influenza was 94.4% among pediatricians, but the respective rates were 70.3% among other doctors and 71.4% among nurses (Table 1). No severe adverse event was found after vaccination. A male pediatrician was diagnosed with the flu using the influenza rapid antigen test.

Immunogenicity

The overall seroconversion rate at day 21 was 43.8% (95%CI, 16.4–71.1). The corresponding seroconversion rate in group A, aged 27–34 y, was 70.0% (95% CI, 35.4–104.5) and in group B, aged ≥ 35 y, was 0.0% (95% CI, 0.0–0.0), respectively. The post-vaccination GMTs at day 21 and the mean GMT fold were higher in group A than in group B. Significant differences were found in baseline GMTs on hemagglutination-inhibition assay between age groups (p = 0.02). The fold increase in GMT of group A was significantly higher than that of group B (p = 0.01). Overall, the seroconversion rate and GMT fold fulfilled the EMEA criteria at 21 d after vaccination, but the seroprotection rate did not meet the requirements. Although the seroprotection rate, seroconversion rate, and GMT fold fulfilled the EMA criteria at 21 d after vaccination in group A, none of the three in group B met the requirements (Table 2).

Table 2. Immune responses, geometric mean titers and fold increases in geometric mean titers, as measured using hemagglutination inhibition (HI) assay after first and second vaccinations with the pandemic influenza a (H1N1) 2009 vaccine

[Reference No.] group age	Group A 27–34 y (n = 10)	Group B 35–49 y (n = 6)	Total 27–49 y (n = 16)	[12] HCP 21–58 y (n = 98)	[13] HCP A 20–29 y (n = 120)	[13] HCP B 30–69 y (n = 268)	[13] HCP total 20–69 y (n = 389)	[14] HCP N.D. (n = 51)	[19] HCP A 20–40 y (n = 50)	[19] HCP B 41–64 y (n = 50)	[19] HCP total 20–64 y (n = 100)	[20] HCP 21–56 y (n = 98)
Seroprotection rate (95% C.I.)
Day 0	10.0 (-12.6, 32.6)	0.0 (0.0, 0.0)	6.3 (-7.1, 19.6)	8.2 (2.7, 13.7)	5.0 (1.0, 8.9)	2.2 (0.5, 4.0)	3.1 (1.4, 4.8)	61 (47.6, 74.4)	44 (30, 58.7)	42 (28.2, 56.8)	43 (31.9, 54.7)	9 (N.D.)
Day 21	70.0 (35.4, 104.5)	0.0 (0.0, 0.0)	43.8 (16.4, 71.1)	78.6 (70.3, 86.8)	45.5 (36.5, 54.5)	34.7 (29.0, 40.0)	38.0 (33.2, 42.9)	96 *1 (96.6, 101.4)	100 (92.9, 100)	100 (92.9, 100)	100 (95.7, 100)	97 (N.D.)
5 mo	80.0 (49.8, 110.2)	0.0 (0.0, 0.0)	50.0 (22.5, 77.5)	N.D.	N.D.	N.D.	N.D.	N.D.	100 *2 (92.9, 100)	100 *2 (92.9, 100)	100 *2 (95.7, 100)	84
Seroconversion rate (95% C.I.)
Day 21	70.0 (35.4, 104.6)	0.00 (0.00, 0.00)	43.8 (16.5, 71.1)	73.5 (63.6, 81.9)	40.5 (31.6, 49.4)	32.1 (26.5, 37.7)	34.7 (30.0, 39.5)	59 *1 (45.5, 72.5)	100 (92.9, 100)	88 (75.7, 95.5)	94 (86.4, 98.1)	88 (N.D.)
5 mo	70.0 (35.4, 104.6)	0.00 (0.00, 0.00)	43.8 (16.5, 71.1)	N.D.	N.D.	N.D.	N.D.	N.D.	100 *2 (92.9, 100)	100 *2 (92.9, 100)	100 *2 (95.7, 100)	75
GMT (95% C.I.)
Day 21	10.7 (7.4, 15.6)	8.9 (7.1, 11.2)	10.0 (7.8, 12.8)	7.9 (6.8, 9.2)	7.0 (6.2, 7.8)	6.1 (5.8, 6.5)	6.4 (6.1, 6.7)	45.8 (37.2, 67.3)	8.9 (7.1, 11.1)	8.6 (6.8, 10.9)	8.8 (7.3, 10.5)	7.7 (6.8, 8.7)
5 mo	56.6 (27.8, 114.9)	8.9 (7.10, 11.2)	27.1 (14.1, 52.2)	73.5 (56.0, 96.4)	28.0 (22.4, 35.0)	20.1 (17.6, 22.8)	22.3 (19.9, 24.9)	196 *1 (146.0, 263.5)	258.3 (191.3, 348.7)	205.3 (145.4, 290)	230.3 (177.7, 298.4)	435.8 (367.7, 516.5)
GMT fold increase (95% C.I.)
	42.9 (24.7, 74.5)	15.9 (10.1,25.0)	29.5 (18.9, 46.2)	N.D.	N.D.	N.D.	N.D.	N.D.	505.6 *2 (427.9, 597.6)	465.3 *2 (384.5, 563)	485 *2 (420.3, 559.7)	160.8 *3 (124.6, 118.6)
Day 21	8.0 (3.0, 13.0)	1.0 (1.0, 1.0)	5.4 (1.9, 8.8)	9.3 (7.3, 11.9)	4.0 (0.4, 36)	3.3 (3.3, 4.9)	3.3 (3.3, 4.9)	4.3 *1 (3.0, 6.1)	29.1 (21.8, 38.9)	3.3 (3.3, 4.9)	3.5 (3.1, 3.9)	113.8 (71.4, 156.2)
5 mo	5.3 (21, 8.5)	1.8 (0.2, 2.3)	4.0 (6.0, 2.0)	N.D.	N.D.	N.D.	N.D.	N.D.	57 *2 (44.3, 73.2)	23.8*2 (17.4, 32.6)	53.9*2 (42.6, 68.1)	99.5*3 (32.0, 166.9)

EMA: seroprotection rate > 70%; seroconversion rate > 40%; GMT fold (95% C.I.) > 2.5; *N.D., not described; *1, day 14; *2, day 42; *3, 3 mo.

Immunogenic persistence

Five months after vaccination, the overall seroprotection rate for pandemic influenza A (H1N1)2009 was 50% (95% CI, 22.5–77.5), remaining above EMA criteria, but the rates were high in group A, 80.0% (95% CI, 49.8–110.2), and low in group B, 0.00% (95% CI, 0.0–0.0). The seroconversion rate of 70.0% (95% CI, 35.4–104.6) of group A over the 5-mo period was higher than the 0.00% (95% CI, 0.0–0.0) of group B. Overall, the GMT increase between observations made before and 5 mo after vaccination was higher in group A (8.0; 95% CI, 3.0, 13.0) than in group B (1.0; 95% CI, 1.0, 1.0) (Table 2).

Discussion

This study examined immunogenicity in the monovalent unadjuvanted inactivated split-virion influenza A (H1N1) pdm09 vaccine in 16 pediatricians. The 94.4% level of vaccination coverage in pediatricians in this study was higher than in Western countries, but a middle-aged male with a low humoral immune response developed moderate flu and took absence on sick leave during the influenza period. Humoral immune response against the vaccine was lower among middle-aged people than among younger people. The first clinical trial to evaluate immunogenicity and safety of the influenza A (H1N1) pdm09 vaccine in Japan, the seroprotection rate, the seroconversion rate, and GMT fold before and 21 d after vaccination, all fulfilled the EMA criteria.¹² Another Japanese hospital reported low humoral immune response consistent with our results. The overall seroprotection rate, seroconversion rate were low and only GMT increase satisfied EMA criterion.¹³ These immune responses of HCPs in Japan were lower than in China.¹⁴

This study has a few limitations. First, the sample size was too small for exact detection of some differences between studies for evaluation of immunogenicity. This small number of participating subjects resulted from the confidentiality of the study when we started because a national policy restricted the research institute to evaluate the immunogenicity of influenza A (H1N1) pdm09 at that time. Therefore, antibody titers of the only pediatricians on behalf of 830 HCPs that were vaccinated were examined. Instead, our study should be regarded as an analysis of the immunogenicity of vaccines against A (H1N1) pdm09 in Japanese pediatricians.

Second, we have not investigated cell mediated immune response to clarify the age-associated difference in immunogenicity. Nevertheless it has been suggested that influenza-specific T-cell responses might be impaired significantly along with aging.^15,16 We divided subjects into two groups incidentally because seroconversion was not detected in subjects aged 36 and over, although the low immune response in the 36–49 age group has not been discussed before. No prior seasonal trivalent influenza vaccine that inhibits the antibody response to the pandemic H1N1 2009 vaccine¹⁷ was administered. Age-related differences of neutralizing antibody responses to strains of A/Uruguay/716/2007 (A/H3N2) and A/ Brisbane/59/2007 (A/H1N1) were not observed (data not shown).

Until very recently, the only adjuvants approved for human use were aluminum salts, which can increase the half-life of an antigen. Newer adjuvants have become available including oil–water mixtures with toll-like receptor triggering ligands.¹⁸ Oil-in-water emulsions, MF59 and AS03, were both used in a monovalent pandemic 2009 influenza A H1N1 vaccine.¹⁸ In the equivalent age group, markedly higher response reported against ad hoc imported AS03-adjuvanted pandemic influenza A (H1N1) vaccine in Japanese HCP¹⁹ as well as in Norwegian HCP (Table 2).²⁰ Compared with these, immunogenicity to pandemic influenza vaccine in this study is not high and unfavorable, even if it is sufficient to fulfill the EMEA criteria. The need remains for an improved adjuvant that enhances immunity to vaccines in Japan.

What else causes low immune response? The influenza vaccine was usually administered subcutaneously in Japan. One reason for low humoral immune response might be subcutaneous administration because the immunogenicity of the intradermal route seems superior to that of the subcutaneous route²¹ One of 16 pediatricians (6.3%) at our hospital contracted pandemic influenza A (H1N1) after the vaccination, and 4 of 154 other medical doctors contracted it (2.6%). At least, pediatricians should be protected against pandemic influenza by a vaccine of particularly high immunogenicity. In July 2011, the Japan Pediatric Society proposed to MHLW that the vaccination route be changed from subcutaneous injection to intramuscular injection, as is done in other countries.²² A subcutaneous route tends to be more reactogenic and is sometimes less immunogenic than the intramuscular route.²³ We approve of this proposal to augment immunogenicity to the greatest degree possible.

New delivery systems currently in development facilitate convenient intradermal vaccination. Efficacy in the clinical trials of influenza vaccination in adults by the intradermal administration route through a novel microinjection system is similar to or better than that by intramuscular injection.^24-26 A few such delivery devices exist, such as the liquid jet injector and the intradermal microinjection system.²⁷ New technology that enhances immunity to vaccines is necessary to improve their clinical efficacy and effectiveness and to reduce influenza-related morbidity and mortality further. Additional investigations and new innovations to optimize immunization are necessary.

Abbreviations:
HCP	=	health care personnel
WHO	=	World Health Organization
ECDC	=	European Centers for Disease Control and Prevention
CDC	=	Centers for Disease Control and Prevention
MHLW	=	The Ministry of Health, Labour and Welfare
EMA	=	European Medicines Agency