H1N1 Vaccine Research Articles

An Optimised Live Attenuated Influenza Vaccine Ferret Efficacy Model Successfully Translates H1N1 Clinical Data

Between 2013 and 2016, the A/H1N1pdm09 component of the live attenuated influenza vaccine (LAIV) produced instances of lower-than-expected vaccine effectiveness. Standard pre-clinical ferret models, using a human-like vaccine dose and focusing on antigenic match to circulating wildtype (wt) strains, were unable to predict these fluctuations. By optimising the vaccine dose and utilising clinically relevant endpoints, we aimed to develop a ferret efficacy model able to reproduce clinical observations. Ferrets were intranasally vaccinated with 4 Log10 FFU/animal (1000-fold reduction compared to clinical dose) of seven historical LAIV formulations with known (19–90%) H1N1 vaccine efficacy or effectiveness (VE). Following homologous H1N1 wt virus challenge, protection was assessed based on primary endpoints of wt virus shedding in the upper respiratory tract and the development of fever. LAIV formulations with high (82–90%) H1N1 VE provided significant protection from wt challenge, while formulations with reduced (19–32%) VE tended not to provide significant protection. The strongest correlation observed was between reduction in wt shedding and VE (R2 = 0.75). Conversely, serum immunogenicity following vaccination was not a reliable indicator of protection (R2 = 0.37). This demonstrated that, by optimisation of the vaccine dose and the use of non-serological, clinically relevant protection endpoints, the ferret model could successfully translate clinical H1N1 LAIV VE data.

Classification of an Individual's Vaccination Status Using Ensemble Hard Voting Classifier

Vaccination is a proactive medical immunization procedure where an inactivated form of a disease-causing agent (such as a virus) is administered to boost the body's defense systems. Efficient management of vaccination status is crucial in healthcare management, disease eradication, community immunity ("herd immunity"), disease prevention, and global health security. Ensuring precise monitoring and validation of an individual's vaccination status is indispensable, especially in the context of emerging diseases and epidemics. This study evaluates the likelihood of individuals obtaining vaccination for the H1N1 virus and the seasonal flu vaccine. Ensemble methods combine the predictions of multiple base classifiers to enhance overall performance. One such method, the hard voting classifier, aggregates the votes from each base classifier and selects the class with the majority vote as the final prediction. This approach leverages the strengths of different classifiers, reducing the risk of individual model biases and improving generalization using metrics such as precision, recall, accuracy, and F1-score are employed to assess the system's effectiveness. The results demonstrate how data-driven methods can address population wellness and improve vaccination rates using an ensemble method. The proposed ensemble hard voting classifier achieved accuracies of 0.905 and 0.907 on the H1N1 and seasonal vaccine datasets, respectively. Using an ensemble approach like the hard voting classifier enhances prediction accuracy and robustness, ultimately leading to better decision making in public health initiatives.

Efficacy and Safety in Dogs Following Administration of an Alphavirus RNA Particle Canine Influenza H3N2 Vaccine.

Canine influenza virus (CIV) H3N2 causes a highly contagious respiratory disease in dogs and has been the source of outbreaks across North America since 2015. An injectable RNA Particle (RP)-CIV H3N2 vaccine has been developed to protect dogs against this disease. To demonstrate efficacy, dogs were randomized into two treatment groups, then vaccinated subcutaneously twice, 21 days apart, with a placebo vaccine (n = 20) or an RP-CIV H3N2 vaccine (n = 20). Three weeks later, dogs were challenged intranasally with virulent CIV H3N2 and observed daily for 10 days for clinical signs of disease. Nasal swabs were also collected daily to evaluate the shedding of the challenge virus. Ten days post-challenge, the dogs were euthanized, and the lungs were examined for consolidation. RP-CIV H3N2 vaccination demonstrated a significant reduction in the duration of clinical signs, duration and amount of virus shed, lung consolidation, and the incidence of suppurative pneumonia. To evaluate safety, dogs from multiple geographic regions were vaccinated subcutaneously, 3-4 weeks apart, with an RP-CIV H3N2 vaccine and observed for adverse events for 14 days after each administration. The RP-CIV H3N2 vaccine was deemed safe, with lethargy being the most reported adverse event at a rate of 1.6%.

Efficacy of the H7N9 vaccine as a candidate for the Korean avian influenza antigen bank

The avian influenza A virus (H7N9), first detected in China in 2013, is a zoonotic virus that remains persistent in bird populations despite a decline in human cases owing to control measures. Therefore, this study aimed to develop a vaccine as one preventive strategy in anticipation of the potential entry of H7N9 into Korea. Using the hemagglutinin and neuraminidase consensus sequences of H7N9 from 2018–2019, a recombinant H7N9 vaccine, rgAPQAH7N9, was developed, and its protective efficacy in specific pathogen-free chickens was evaluated. The rgAPQAH7N9 vaccine exhibited proliferation in eggs and demonstrated high immunogenicity, with a hemagglutination inhibition titer of 9.3 log2. Furthermore, the vaccine provided complete protection, as vaccinated chickens did not exhibit clinical signs or viral shedding. Moreover, when the rgAPQAH7N9 vaccine was boosted, the resulting immunity was long-lasting, with hemagglutination inhibition titers > 7 log2 persisting after 6 months. Therefore, the rgAPQAH7N9 vaccine virus may be considered a potential candidate for inclusion in the avian influenza antigen bank to ensure preparedness for emergency vaccination in poultry.

Cistanche deserticola polysaccharide-functionalized dendritic fibrous nano-silica as oral delivery system for H9N2 vaccine to promote systemic and mucosal immune response.

Most infectious diseases are caused by pathogens that invade the body tissues through mucosal tract. Therefore, it is essential to develop effective vaccines administered through the mucosa as a first-line of defense against major infectious diseases. Oral delivery of vaccines is currently of great interest due to its potential to elicit both mucosal and systemic immune responses, high compliance rate and non-invasive nature. However, their development is limited by the challenging gastrointestinal (GI) environment, the low permeability of the mucus barrier, and the lack of effective and safe mucosal adjuvants. Currently, nanoparticle-based strategies show significant potential for improving oral vaccine delivery systems. Herein, the dendritic fibrous nano-silica (DFNS) grafted with Cistanche deserticola polysaccharide (CDP) nanoparticles (CDP-DFNS) were developed for oral delivery of H9N2 antigen. CDP-DFNS induced the activation of macrophages, thereby enhancing antigen uptake in vitro. Additionally, CDP-DFNS/H9N2 significantly activated the dendritic cells (DCs) in Peyer's patches (PPs), and T/B cells in mesenteric lymph nodes (MLNs). Moreover, CDP-DFNS/H9N2 enhanced the HI titers and levels of H9N2-specific antibody IgG, secretory IgA (SIgA) and H9N2-specific IgA in intestinal and respiratory mucosa, as well as Th-associated cytokines. Our results indicate that CDP-DFNS could be a promising oral vaccine adjuvant delivery system.

Recent Occurrence, Diversity, and Candidate Vaccine Virus Selection for Pandemic H5N1: Alert Is in the Air.

The prevalence of the highly pathogenic avian influenza virus H5N1 in wild birds that migrate all over the world has resulted in the dissemination of this virus across Asia, Europe, Africa, North and South America, the Arctic continent, and Antarctica. So far, H5N1 clade 2.3.4.4.b has reached an almost global distribution, with the exception of Australia and New Zealand for autochthonous cases. H5N1 clade 2.3.4.4.b, derived from the broad-host-range A/Goose/Guangdong/1/96 (H5N1) lineage, has evolved, adapted, and spread to species other than birds, with potential mammal-to-mammal transmission. Many public health agencies consider H5N1 influenza a real pandemic threat. In this sense, we analyzed H5N1 hemagglutinin sequences from recent outbreaks in animals, clinical samples, antigenic prototypes of candidate vaccine viruses, and licensed human vaccines for H5N1 with the aim of shedding light on the development of an H5N1 vaccine suitable for a pandemic response, should one occur in the near future.

Preparation and Antigenic Site Identification of Monoclonal Antibodies against PB1 Protein of H9N2 Subtype AIV.

Recently, low pathogenic avian influenza virus (LPAIV), including H9N2 subtype, has been common clinical epidemic strains, and is widely distributed globally. The PB1 protein is a key component of the viral RNA polymerase complex (vRNP), and is vital to viral transcription and translation. In this study, to investigate the antigenic determinants in the PB1 protein, the truncated PB1 sequence (1bp-735bp) from H9N2 subtype AIV was amplified with PCR, and expressed in plasmid pET-28a (+). After purification, the recombinant PB1 protein was used to immunize BALB/c mice. Following immunization, hybridoma cells producing PB1-specific monoclonal antibodies were generated through the fusion of splenic lymphocytes with SP2/0 cells. Then, four stable hybridoma cell lines (5F12, 5B3, 2H9, and 3E6) were screened using indirect ELISA and Western blotting. Furthermore, two antigenic sites, 67NPIDGPLPED76 and 97ESHPGIFENS106, were identified through the construction of truncated overlapping fragments of the PB1 protein. These sites were conserved among 28 AIV strains, and were located on the PB1 protein surface. The findings offer a theoretical reference for the development and improvement of H9N2 vaccines and offer biological materials for virus detection during AIV infection mechanisms.

Extraction and immunomodulatory effects of acid Lagenaria siceraria (Molina) Standl. Polysaccharide on chickens

Herbal polysaccharides are extensively studied as vaccine adjuvants due to their safety and potent immunoenhancing activity. This study aimed to analyze the structure of Lagenaria siceraria (Molina) Standl polysaccharide (LSP50) and investigate its adjuvant activity for the H9N2 vaccine in broiler chickens. Structural analysis revealed that LSP50 primarily consisted of rhamnose, arabinose, xylose, mannose, glucose, and galactose with molar ratios of 23.12: 12.28: 10.87: 8.26: 2.64: 22.82 respectively. The adjuvant activity of LSP50 was evaluated, which showing significant enhancements compared to the H9N2 group. Parameters including the immune organ index, H9N2 specific IgG level, cytokines contents (IFN-γ, IL-2, IL-4, and IL-5), and the proportion of CD3e+CD8aT+cells were significantly increased in the LSP50 group (P < 0.05). Additionally, sequencing results showed that LSP50 modulates the immune response by regulating PLA2G12B and PTGDS genes involved in the arachidonic acid pathway. These findings were further validated through qPCR analysis to affirm the reliability of the sequencing data. In conclusion, our results demonstrate that LSP50 exhibits potent adjuvant activity, enhancing both cellular and humoral immunity.

The V223I substitution in hemagglutinin reduces the binding affinity to human-type receptors while enhancing the thermal stability of the H3N2 canine influenza virus.

Given the intimate relationship between humans and dogs, the H3N2 canine influenza viruses (CIVs) pose a threat to public health. In our study, we isolated four H3N2 CIVs from 3,758 dog nasal swabs in China between 2018 and 2020, followed by genetic and biological analysis. Phylogenetic analysis revealed 15 genotypes among all available H3N2 CIVs, with genotype 15 prevailing among dogs since around 2017, indicating the establishment of a stable virus lineage in dogs. Molecular characterization identified many mammalian adaptive substitutions, including HA-G146S, HA-N188D, PB2-I292T, PB2-G590S, PB2-S714I, PB1-D154G, and NP-R293K, present across the four isolates. Notably, analysis of HA sequences uncovered a newly emerged adaptive mutation, HA-V223I, which is predominantly found in human and swine H3N2 viruses, suggesting its role in mammalian adaptation. Receptor-binding analysis revealed that the four H3N2 viruses bind both avian and human-type receptors. However, HA-V223I decreases the H3N2 virus's affinity for human-type receptors but enhances its thermal stability. Furthermore, attachment analysis confirmed the H3N2 virus binding to human tracheal tissues, albeit with reduced affinity when the virus carries HA-V223I. Antigenic analysis indicated that the current human H3N2 vaccines do not confer protection against H3N2 CIVs. Collectively, these findings underscore that the potential threat posed by H3N2 CIVs to human health still exists, emphasizing the necessity of close surveillance and monitoring of H3N2 CIVs in dogs.

Licensed H5N1 vaccines generate cross-neutralizing antibodies against highly pathogenic H5N1 clade 2.3.4.4b influenza virus.

The emergence of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b viruses and their transmission to dairy cattle and animals, including humans, poses a major global public health threat. Therefore, the development of effective vaccines and therapeutics against H5N1 clade 2.3.4.4b virus is considered a public health priority. In the United States, three H5N1 vaccines derived from earlier strains of HPAI H5N1 (A/Vietnam, clade 1, and A/Indonesia, clade 2.1) virus, with (MF59 or AS03) or without adjuvants, are licensed and stockpiled for pre-pandemic preparedness, but whether they can elicit neutralizing antibodies against circulating H5N1 clade 2.3.4.4b viruses is unknown. In this study, we evaluated the binding, hemagglutination inhibition and neutralizing antibody response generated after vaccination of adults with the three licensed vaccines. Individuals vaccinated with the two adjuvanted licensed H5N1 vaccines generated cross-reactive binding and cross-neutralizing antibodies against the HPAI clade 2.3.4.4b A/Astrakhan/3212/2020 virus. Seroconversion rates of 60-95% against H5 clade 2.3.4.4b were observed after two doses of AS03-adjuvanted-A/Indonesia or three doses of MF59-adjuvanted-A/Vietnam vaccine. These findings suggest that the stockpiled US-licensed adjuvanted H5N1 vaccines generate cross-neutralizing antibodies against circulating HPAI H5N1 clade 2.3.4.4b in humans and may be useful as bridging vaccines until updated H5N1 vaccines become available.

A synthetic TLR4 agonist significantly increases humoral immune responses and the protective ability of an MDCK-cell-derived inactivated H7N9 vaccine in mice.

Antigenically divergent H7N9 viruses pose a potential threat to public health, with the poor immunogenicity of candidate H7N9 vaccines demonstrated in clinical trials underscoring the urgent need for more-effective H7N9 vaccines. In the present study, mice were immunized with various doses of a suspended-MDCK-cell-derived inactivated H7N9 vaccine, which was based on a low-pathogenic H7N9 virus, to assess cross-reactive immunity and cross-protection against antigenically divergent H7N9 viruses. We found that the CRX-527 adjuvant, a synthetic TLR4 agonist, significantly enhanced the humoral immune responses of the suspended-MDCK-cell-derived H7N9 vaccine, with significant antigen-sparing and immune-enhancing effects, including robust virus-specific IgG, hemagglutination-inhibiting (HI), neuraminidase-inhibiting (NI), and virus-neutralizing (VN) antibody responses, which are crucial for protection against influenza virus infection. Moreover, the CRX-527-adjuvanted H7N9 vaccine also elicited cross-protective immunity and cross-protection against a highly pathogenic H7N9 virus with a single vaccination. Notably, NI and VN antibodies might play an important role in cross-protection against lethal influenza virus infections. This study showed that a synthetic TLR4 agonist adjuvant has a potent immunopotentiating effect, which might be considered worth further development as a means of increasing vaccine effectiveness.

A Dialogue about Vaccine Side Effects: Understanding Difficult Pandemic Experiences.

This paper investigates the relationship between the experiences of mass vaccinations against two pandemic viruses: the swine flu in 2009-2010 and COVID-19 in the early 2020s. We show how distressing memories from the swine flu vaccination, which led to the rare but severe adverse effect of narcolepsy in approximately 500 children in Sweden, were triggered by the COVID-19 pandemic. The narcolepsy illness story has rarely been told in academic contexts; therefore, we will provide space for this story. It is presented through a dialogue with the aim of shedding light on the interrelationship between pandemics-and between mass vaccinations-to investigate what could be termed cultural wounds that influence societies because they are characterized by the difficulty of talking about them. The paper explores the multiple shocks of illness in life and what can be learned from them by sharing them.

DEVELOPMENT OF HIGHLY PATHOGENIC AVIAN INFLUENZA VACCINE FOR PANDEMIC INFLUENZA PREPAREDNESS: A REVIEW

The Highly Pathogenic Avian Influenza (HPAI) H5N1 virus caused extraordinary incidents in several countries, especially Asia, Africa, and Europe. The disease's fatality rate caused by the H5N1 virus reaches 60%. This incident raised concerns about a wider HPAI H5N1 virus pandemic if effective human-to-human transmission occurred. Therefore, the World Health Organization (WHO) calls on all countries to prepare themselves for a pandemic that may occur. One of the strategies in preparation for this pandemic is to develop a vaccine. So far, vaccines are effective in disease prevention efforts because they can work to trigger a natural immune response and induce a memory response against the pathogen in question. Several strategies are needed to develop an effective influenza vaccine in carrying out vaccine development research and in-depth understanding of (i) virology, (ii) virus life cycle, (iii) host immune response to infection, (iv) pathology, and (v) HPAI H5N1 vaccine development strategy. Until now, many HPAI H5N1 vaccines have been developed, from vaccines developed using conventional methods to alternative vaccines using more modern methods. The results of the development of the vaccine are expected to provide provisions for a possible pandemic caused by the HPAI H5N1 virus. Keywords : Influenza, virus, vaccine

Natural variation in neuraminidase activity influences the evolutionary potential of the seasonal H1N1 lineage hemagglutinin.

The antigenic evolution of the influenza A virus hemagglutinin (HA) gene poses a major challenge for the development of vaccines capable of eliciting long-term protection. Prior efforts to understand the mechanisms that govern viral antigenic evolution mainly focus on HA in isolation, ignoring the fact that HA must act in concert with the viral neuraminidase (NA) during replication and spread. Numerous studies have demonstrated that the degree to which the receptor-binding avidity of HA and receptor-cleaving activity of NA are balanced with each other influences overall viral fitness. We recently showed that changes in NA activity can significantly alter the mutational fitness landscape of HA in the context of a lab-adapted virus strain. Here, we test whether natural variation in relative NA activity can influence the evolutionary potential of HA in the context of the seasonal H1N1 lineage (pdmH1N1) that has circulated in humans since the 2009 pandemic. We observed substantial variation in the relative activities of NA proteins encoded by a panel of H1N1 vaccine strains isolated between 2009 and 2019. We comprehensively assessed the effect of NA background on the HA mutational fitness landscape in the circulating pdmH1N1 lineage using deep mutational scanning and observed pronounced epistasis between NA and residues in or near the receptor-binding site of HA. To determine whether NA variation could influence the antigenic evolution of HA, we performed neutralizing antibody selection experiments using a panel of monoclonal antibodies targeting different HA epitopes. We found that the specific antibody escape profiles of HA were highly contingent upon NA background. Overall, our results indicate that natural variation in NA activity plays a significant role in governing the evolutionary potential of HA in the currently circulating pdmH1N1 lineage.

Evaluation of Efficacy of Surface Coated versus Encapsulated Influenza Antigens in Mannose-Chitosan Nanoparticle-Based Intranasal Vaccine in Swine.

This study focuses on the development and characterization of an intranasal vaccine platform using adjuvanted nanoparticulate delivery of swine influenza A virus (SwIAV). The vaccine employed whole inactivated H1N2 SwIAV as an antigen and STING-agonist ADU-S100 as an adjuvant, with both surface adsorbed or encapsulated in mannose-chitosan nanoparticles (mChit-NPs). Optimization of mChit-NPs included evaluating size, zeta potential, and cytotoxicity, with a 1:9 mass ratio of antigen to NP demonstrating high loading efficacy and non-cytotoxic properties suitable for intranasal vaccination. In a heterologous H1N1 pig challenge trial, the mChit-NP intranasal vaccine induced cross-reactive sIgA antibodies in the respiratory tract, surpassing those of a commercial SwIAV vaccine. The encapsulated mChit-NP vaccine induced high virus-specific neutralizing antibody and robust cellular immune responses, while the adsorbed vaccine elicited specific high IgG and hemagglutinin inhibition antibodies. Importantly, both the mChit-NP vaccines reduced challenge heterologous viral replication in the nasal cavity higher than commercial swine influenza vaccine. In summary, a novel intranasal mChit-NP vaccine platform activated both the arms of the immune system and is a significant advancement in swine influenza vaccine design, demonstrating its potential effectiveness for pig immunization.

Evolution and Antigenic Differentiation of Avian Influenza A(H7N9) Virus, China.

We characterized the evolution and molecular characteristics of avian influenza A(H7N9) viruses isolated in China during 2021-2023. We systematically analyzed the 10-year evolution of the hemagglutinin gene to determine the evolutionary branch. Our results showed recent antigenic drift, providing crucial clues for updating the H7N9 vaccine and disease prevention and control.

A ferritin nanoparticle vaccine based on the hemagglutinin extracellular domain of swine influenza A (H1N1) virus elicits protective immune responses in mice and pigs.

Swine influenza viruses (SIVs) pose significant economic losses to the pig industry and are a burden on global public health systems. The increasing complexity of the distribution and evolution of different serotypes of influenza strains in swine herds escalates the potential for the emergence of novel pandemic viruses, so it is essential to develop new vaccines based on swine influenza. Here, we constructed a self-assembling ferritin nanoparticle vaccine based on the hemagglutinin (HA) extracellular domain of swine influenza A (H1N1) virus using insect baculovirus expression vector system (IBEVS), and after two immunizations, the immunogenicities and protective efficacies of the HA-Ferritin nanoparticle vaccine against the swine influenza virus H1N1 strain in mice and piglets were evaluated. Our results demonstrated that HA-Ferritin nanoparticle vaccine induced more efficient immunity than traditional swine influenza vaccines. Vaccination with the HA-Ferritin nanoparticle vaccine elicited robust hemagglutinin inhibition titers and antigen-specific IgG antibodies and increased cytokine levels in serum. MF59 adjuvant can significantly promote the humoral immunity of HA-Ferritin nanoparticle vaccine. Furthermore, challenge tests showed that HA-Ferritin nanoparticle vaccine conferred full protection against lethal challenge with H1N1 virus and significantly decreased the severity of virus-associated lung lesions after challenge in both BALB/c mice and piglets. Taken together, these results indicate that the hemagglutinin extracellular-based ferritin nanoparticle vaccine may be a promising vaccine candidate against SIVs infection.

Inactivated H9N2 vaccines developed with early strains do not protect against recent H9N2 viruses: Call for a change in H9N2 control policy

Inactivated H9N2 vaccines developed with early strains do not protect against recent H9N2 viruses: Call for a change in H9N2 control policy

Safety, Tolerability, and Immunogenicity of aH5N1 Vaccine in Adults with and without Underlying Medical Conditions.

Influenza pandemics pose a serious risk to the global population, with the potential for high morbidity and mortality. An adjuvanted H5N1 vaccine (aH5N1) has been approved for prophylaxis against the avian influenza virus H5N1, which is a likely cause of future pandemics. In this phase-III, stratified, randomized, controlled, observer-blind, multicenter study, we evaluated the safety and immunogenicity of aH5N1 in four separate groups of adults: adults 18-60 years of age who were healthy or had high-risk medical conditions and older adults ≥61 years of age who were healthy or had high-risk medical conditions. Subjects were randomly assigned to aH5N1 or the comparator, adjuvanted trivalent seasonal influenza vaccine (aTIV). Antibody responses to aH5N1 were increased in all four subgroups and, within each age stratum, largely consistent between healthy subjects and those with medical conditions. Injection-site pain was reported by 66-73% of younger and 36-42% of older-aH5N1 recipients, and fatigue and myalgia were reported by 22-41% of subjects across age and health subgroups. No serious adverse events or deaths were considered related to the study vaccine. In conclusion, aH5N1 increased antibody responses regardless of age or health status and demonstrated a clinically acceptable safety and tolerability profile.

THE IMMUNITY DURATION AND INTENSITY IN INDUSTRIAL LAYING HENS FOLLOWING VACCINATION WITH INACTIVATED H5N1 AVIAN INFLUENZA VACCINE

After the severe AIV H5 outbreak in Kazakhstan in 2020 the extensive use of AIV H5 vaccines started in the industrial poultry farms to limit the H5N1 influenza spread. Traditional methods, such as stamping out are no longer a viable option in countries where Highly Pathogenic Avian Influenza (HPAI) has become endemic. However, available vaccines and vaccination protocols have been widely researched in laboratory conditions, and limited testing has been conducted on commercial layers for the immunity persistence in field conditions. Immunity persistence after AIV vaccination can be quite different between laboratory and field conditions. Our basic goal was to assess the intensity and duration of immunity in commercial layers following 1, 2 and 3 vaccinations. H5N1 hemagglutination inhibition (HI) antibodies were observed 370 days after vaccination of chickens using three schemes of vaccination. However, at 370 days post vaccination 1 experimental group obtaining one vaccination had comparatively low HI titers (mean titer 6,5±1,2 log2), the other two groups having two and three vaccinations showed 8,8±2,4 mean log2 and 9,4±2,2 mean log2 respectively. The described results showed that inactivated H5N1 vaccine can produce lengthy, intense and homogenous immunity under field conditions following 2 and 3 vaccinations.