Immunogenicity and efficacy of one and two doses of Ad26.COV2.S COVID vaccine in adult and aged NHP

Safe and effective coronavirus disease–19 (COVID-19) vaccines are urgently needed to control the ongoing pandemic. While single-dose vaccine regimens would provide multiple advantages, two doses may improve the magnitude and durability of immunity and protective efficacy. We assessed one- and two-dose regimens of the Ad26.COV2.S vaccine candidate in adult and aged nonhuman primates (NHPs). A two-dose Ad26.COV2.S regimen induced higher peak binding and neutralizing antibody responses compared with a single dose. In one-dose regimens, neutralizing antibody responses were stable for at least 14 wk, providing an early indication of durability. Ad26.COV2.S induced humoral immunity and T helper cell (Th cell) 1–skewed cellular responses in aged NHPs that were comparable to those in adult animals. Aged Ad26.COV2.S-vaccinated animals challenged 3 mo after dose 1 with a SARS-CoV-2 spike G614 variant showed near complete lower and substantial upper respiratory tract protection for both regimens. Neutralization of variants of concern by NHP sera was reduced for B.1.351 lineages while maintained for the B.1.1.7 lineage independent of Ad26.COV2.S vaccine regimen.     

Plasma and memory antibody responses to Gamma SARS-CoV-2 provide limited cross-protection to other variants

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to be a global problem in part because of the emergence of variants of concern that evade neutralization by antibodies elicited by prior infection or vaccination. Here we report on human neutralizing antibody and memory responses to the Gamma variant in a cohort of hospitalized individuals. Plasma from infected individuals potently neutralized viruses pseudotyped with Gamma SARS-CoV-2 spike protein, but neutralizing activity against Wuhan-Hu-1-1, Beta, Delta, or Omicron was significantly lower. Monoclonal antibodies from memory B cells also neutralized Gamma and Beta pseudoviruses more effectively than Wuhan-Hu-1. 69% and 34% of Gamma-neutralizing antibodies failed to neutralize Delta or Wuhan-Hu-1. Although Class 1 and 2 antibodies dominate the response to Wuhan-Hu-1 or Beta, 54% of antibodies elicited by Gamma infection recognized Class 3 epitopes. The results have implications for variant-specific vaccines and infections, suggesting that exposure to variants generally provides more limited protection to other variants.     

Thrombotic Thrombocytopenic Purpura after Ad26.COV2-S Vaccination

The U.S. Food and Drug Administration (FDA) recently issued an Emergency Use Authorization (EUA) for two highly effective Sars-CoV-2 (COVID-19) vaccines from Pfizer-BioNTech and Moderna. More recently, EUA was granted for the Johnson and Johnson COVID-19 vaccine which uses traditional virus-based technology. In this vaccine, researchers added the gene for the coronavirus spike protein to modified Adenovirus 26 and named it Ad26.COV2-S. Nearly 7 million doses of the Ad26.COV2-S have been administered as of mid-April 2021. Recently the Federal Drug Administration and Center for Disease Control and Prevention reviewed data involving six reported cases in the United States of cerebral venous sinus thrombosis in combination with thrombocytopenia in people who received the vaccination. All cases were in women between 18 and 48, with symptoms developing six to 13 days after vaccination. A recent study in the United Kingdom reported similar events in 23 patients age 21 to 77, 61% of which were female, with cases of presumed vaccine induced thrombosis and thrombocytopenia occurring six to 24 days after vaccination.We report a 62-year-old female who presented to the emergency department (ED) with acute onset of altered mental status. She had received the Ad26.COV2-S vaccine 37 days prior to ED presentation. She developed thrombotic thrombocytopenic purpura (TTP) and no other cause was found. To our knowledge this is the first case in the United States of thrombotic thrombocytopenic purpura after receiving the Ad26.COV2-S COVID-19 vaccine.     

Omicron variant (B.1.1.529) of SARS-CoV-2: Mutation,infectivity, transmission,and vaccine resistance

The appearance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant Omicron (B.1.1.529) has caused panic responses around the world because of its high transmission rate and number of mutations. This review summarizes the highly mutated regions, the essential infectivity, transmission, vaccine breakthrough and antibody resistance of the Omicron variant of SARS-CoV-2. The Omicron is highly transmissible and is spreading faster than any previous variant, but may cause less severe symptoms than previous variants. The Omicron is able to escape the immune system’s defenses and coronavirus disease 2019 vaccines are less effective against the Omicron variant. Early careful preventive steps including vaccination will always be key for the suppression of the Omicron variant.     

Potent human broadly SARS-CoV-2–neutralizing IgA and IgG antibodies effective against Omicron BA.1 and BA.2

Memory B-cell and antibody responses to the SARS-CoV-2 spike protein contribute to long-term immune protection against severe COVID-19, which can also be prevented by antibody-based interventions. Here, wide SARS-CoV-2 immunoprofiling in Wuhan COVID-19 convalescents combining serological, cellular, and monoclonal antibody explorations revealed humoral immunity coordination. Detailed characterization of a hundred SARS-CoV-2 spike memory B-cell monoclonal antibodies uncovered diversity in their repertoire and antiviral functions. The latter were influenced by the targeted spike region with strong Fc-dependent effectors to the S2 subunit and potent neutralizers to the receptor-binding domain. Amongst those, Cv2.1169 and Cv2.3194 antibodies cross-neutralized SARS-CoV-2 variants of concern, including Omicron BA.1 and BA.2. Cv2.1169, isolated from a mucosa-derived IgA memory B cell demonstrated potency boost as IgA dimers and therapeutic efficacy as IgG antibodies in animal models. Structural data provided mechanistic clues to Cv2.1169 potency and breadth. Thus, potent broadly neutralizing IgA antibodies elicited in mucosal tissues can stem SARS-CoV-2 infection, and Cv2.1169 and Cv2.3194 are prime candidates for COVID-19 prevention and treatment.     

Trivalent nucleoside-modified mRNA vaccine yields durable memory B cell protection against genital herpes in preclinical models

Nucleoside-modified mRNA vaccines have gained global attention because of COVID-19. We evaluated a similar vaccine approach for preventing a chronic, latent genital infection rather than an acute respiratory infection. We used animal models to compare an HSV-2 trivalent nucleoside-modified mRNA vaccine with the same antigens prepared as proteins, with an emphasis on antigen-specific memory B cell responses and immune correlates of protection. In guinea pigs, serum neutralizing-antibody titers were higher at 1 month and declined far less by 8 months in mRNA- compared with protein-immunized animals. Both vaccines protected against death and genital lesions when infected 1 month after immunization; however, protection was more durable in the mRNA group compared with the protein group when infected after 8 months, an interval representing greater than 15% of the animal’s lifespan. Serum and vaginal neutralizing-antibody titers correlated with protection against infection, as measured by genital lesions and vaginal virus titers 2 days after infection. In mice, the mRNA vaccine generated more antigen-specific memory B cells than the protein vaccine at early times after immunization that persisted for up to 1 year. High neutralizing titers and robust B cell immune memory likely explain the more durable protection by the HSV-2 mRNA vaccine.     

Clinical update of the AS04-Adjuvanted human Papillomavirus-16/18 cervical cancer vaccine,cervarix®

Persistent infection with human papillomavirus (HPV) is a necessary cause of cervical cancer, resulting annually in 274,000 deaths worldwide. Two prophylactic HPV vaccines are licensed in >100 countries, and immunization programs in young, adolescent girls have been widely implemented. HPV-16/18 AS04-adjuvanted vaccine (Cervarix®; GlaxoSmithKline Biologicals, Rixensart, Belgium) has demonstrated type-specific protection against the five most frequent cancer-causing types (16, 18, 31, 33, and 45) that are responsible for 82% of invasive cervical cancers globally. Cervarix® has demonstrated efficacy against HPV-45, which is the third most common HPV type in cervical cancer and adenocarcinoma. Final results of a large phase 3 trial recently showed Cervarix® substantially reduced the overall burden of cervical precancerous lesions (cervical intraepithelial neoplasia 2+) by 70.2% in an HPV-naïve population approximating young girls prior to sexual debut, the target of most current vaccination programs. Protection offered by Cervarix® against nonvaccine types (mainly 31, 33, and 45) might potentially allow for 11%–16% additional protection against cervical cancers, compared to a vaccine only offering protection against HPV-16/18. Another recent study directly compared the antibody response of Cervarix® to that of quadrivalent HPV-6/11/16/18 vaccine (Gardasil®; Merck, Whitehouse Station, NJ, USA). Cervarix® induced significantly superior neutralizing antibody levels as compared with Gardasil® for HPV-16 and HPV-18 in all age groups studied. This may translate into more women having detectable (neutralizing) antibodies in cervicovaginal secretions for HPV-16 and HPV-18 after vaccination with Cervarix® when compared with Gardasil®. Cervarix® induced significantly higher frequencies of antigen-specific memory B-cells and T-cells in responders for HPV-16 and HPV-18 as compared with Gardasil®. Cervarix® continues to show sustained high levels of total and neutralizing antibodies for HPV-16 and HPV-18, 7.3 years after vaccination. This is associated with high efficacy and no breakthrough cases in the HPV-naïve population, and is the longest duration follow-up for safety, immunogenicity, and efficacy for any licensed HPV vaccine to date.     

The Israeli study of Pfizer BNT162b2 vaccine in pregnancy: considering maternal and neonatal benefits

Pregnant patients with COVID-19 are more likely to require intensive care and die compared with noninfected pregnant women. While the consequences of COVID-19 disease in pregnancy prompted many health care organizations to support vaccination in pregnancy, vaccine effects for mother and infant remained unclear. In this issue of the JCI, Beharier and Mayo et al. explored maternal and neonatal responses to the Pfizer BNT162b2 SARS-CoV-2 mRNA vaccine. The authors examined blood samples from women and cord blood of neonates following childbirth. Samples were stratified into three groups: vaccine recipients, unvaccinated participants with past positive SARS-CoV-2 test, and unvaccinated participants without prior infection. Vaccinated mothers and mothers with previous infection generated and transferred protective IgG antibodies across the placenta. This study provides evidence to support the safety and efficacy of COVID-19 vaccination in pregnancy with protection to the neonate against infection, outlining clear vaccine benefits for both maternal and child health.     

Efficacy and safety of mRNA SARS-CoV-2 vaccines in lung transplant recipients

BackgroundTo date, reports addressing the antibody response following mRNA SARS-CoV-2 vaccination in lung transplant (LTX) recipients are limited. Thus, the aim of this clinical study was to investigate the efficacy and safety of the vaccines in LTX recipients compared to controls.MethodsAn open-label, nonrandomized prospective study was conducted at Tohoku University Hospital. LTX recipients and controls who received either the BNT162b2 vaccine or the mRNA-1273 vaccine were recruited, and SARS-CoV-2 IgG was measured before and after vaccination. The adverse events were reviewed. Predictors of negative serology after vaccination were evaluated with logistic regression.ResultsForty-one LTX recipients and 24 controls were analyzed. Although all controls had a positive antibody response to a SARS-CoV-2 mRNA vaccine, antibody response was found in 24.4% of LTX recipients (p < .0001). The amount of SARS-CoV-2 IgG following the 2nd dose significantly climbed to 6557 AU/mL in controls, whereas the increase in IgG in LTX recipients was 8.3 AU/mL (p < .0001). Fewer LTX recipients developed systemic fever than controls (p < .0001) despite equivalent overall adverse event percentages in both groups. A higher plasma concentration of mycophenolate was a significant predictor of negative serology (p = .032).ConclusionsAn impaired antibody response to mRNA vaccines was significantly found in LTX recipients compared to controls and was associated with the plasma concentration of mycophenolate. While repeating mRNA vaccination may be one of the strategies to improve antibody response given the safety of the vaccines, emerging data on humoral immune responses based on immunosuppression regimens in LTX recipients should be studied (jRCT1021210009).     

Adenovirus-based genetic vaccines for biodefense

The robust host responses elicited against transgenes encoded by (E1-)(E3-) adenovirus (Ad) gene transfer vectors can be used to develop Ad-based vectors as platform technologies for vaccines against potential bioterror pathogens. This review focuses on pathogens of major concern as bioterror agents and why Ad vectors are ideal as anti-bioterror vaccine platforms, providing examples from our laboratories of using Ad vectors as vaccines against potential bioterror pathogens and how Ad vectors can be developed to enhance vaccine efficacy in the bioterror war.     

An antibody targeting the N-terminal domain of SARS-CoV-2 disrupts the spike trimer

The protective human antibody response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) focuses on the spike (S) protein, which decorates the virion surface and mediates cell binding and entry. Most SARS-CoV-2 protective antibodies target the receptor-binding domain or a single dominant epitope (“supersite”) on the N-terminal domain (NTD). Using the single B cell technology called linking B cell receptor to antigen specificity through sequencing (LIBRA-Seq), we isolated a large panel of NTD-reactive and SARS-CoV-2–neutralizing antibodies from an individual who had recovered from COVID-19. We found that neutralizing antibodies against the NTD supersite were commonly encoded by the IGHV1-24 gene, forming a genetic cluster representing a public B cell clonotype. However, we also discovered a rare human antibody, COV2-3434, that recognizes a site of vulnerability on the SARS-CoV-2 S protein in the trimer interface (TI) and possesses a distinct class of functional activity. COV2-3434 disrupted the integrity of S protein trimers, inhibited the cell-to-cell spread of the virus in culture, and conferred protection in human angiotensin-converting enzyme 2–transgenic (ACE2-transgenic) mice against the SARS-CoV-2 challenge. This study provides insight into antibody targeting of the S protein TI region, suggesting this region may be a site of virus vulnerability.     

A dual-antigen self-amplifying RNA SARS-CoV-2 vaccine induces potent humoral and cellular immune responses and protects against SARS-CoV-2 variants through T cell-mediated immunity

Self-amplifying RNA vaccines may induce equivalent or more potent immune responses at lower doses compared to non-replicating mRNA vaccines via amplified antigen expression. In this paper, we demonstrate that 1 μg of an LNP-formulated dual-antigen self-amplifying RNA vaccine (ZIP1642), encoding both the S-RBD and N antigen, elicits considerably higher neutralizing antibody titers against Wuhan-like Beta B.1.351 and Delta B.1.617.2 SARS-CoV-2 variants compared to those of convalescent patients. In addition, ZIP1642 vaccination in mice expanded both S- and N-specific CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells and caused a Th1 shifted cytokine response. We demonstrate that the induction of such dual antigen-targeted cell-mediated immune response may provide better protection against variants displaying highly mutated Spike proteins, as infectious viral loads of both Wuhan-like and Beta variants were decreased after challenge of ZIP1642 vaccinated hamsters. Supported by these results, we encourage redirecting focus toward the induction of multiple antigen-targeted cell-mediated immunity in addition to neutralizing antibody responses to bypass waning antibody responses and attenuate infectious breakthrough and disease severity of future SARS-CoV-2 variants.     

Impact of preexisting vector immunity on the efficacy of adeno-associated virus-based HIV-1 Gag vaccines

Vectors based on primate-derived adeno-associated virus (AAV) are being considered in the development of genetic vaccines against a number of diseases including infection with HIV-1. Preexisting immunity to the vaccine carrier as a result of natural infections could potentially compromise vaccine efficacy. This study evaluates the impact of neutralizing antibodies against AAV capsids on the ability of HIV-1 Gag-expressing vectors to elicit transgene-specific T and B cell responses. Mice were passively transferred with pooled human immunoglobulin at various doses to simulate human antivector humoral immunity. Vectors based on serotype 2, which were evaluated in the clinic, were compared with those created from the novel monkey isolates AAV7 and AAV8. Inhibition of AAV2-directed Gag responses occurred at doses of human immunoglobulin 10- to 20-fold less than was required to inhibit immunogenicity of AAV7 and AAV8 vectors. Cynomolgus macaques were screened for preexisting immunity to AAV7 and AAV8 and sera from individual animals were passively transferred into mice that were analyzed for AAV vaccine efficacy. There was a correlation between the level of preexisting capsid neutralizing titers and diminution of vaccine efficacy; sera from a number of animals with no detectable neutralizing antibodies showed partial vaccine inhibition, suggesting that the in vitro assay is less sensitive than the in vivo passive transfer assay for detecting neutralizing antibodies to AAV.     

Single-dose replicating poxvirus vector-based RBD vaccine drives robust humoral and T cell immune response against SARS-CoV-2 infection

The coronavirus disease 2019 (COVID-19) pandemic requires the continued development of safe, long-lasting, and efficacious vaccines for preventive responses to major outbreaks around the world, and especially in isolated and developing countries. To combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we characterize a temperature-stable vaccine candidate (TOH-Vac1) that uses a replication-competent, attenuated vaccinia virus as a vector to express a membrane-tethered spike receptor binding domain (RBD) antigen. We evaluate the effects of dose escalation and administration routes on vaccine safety, efficacy, and immunogenicity in animal models. Our vaccine induces high levels of SARS-CoV-2 neutralizing antibodies and favorable T cell responses, while maintaining an optimal safety profile in mice and cynomolgus macaques. We demonstrate robust immune responses and protective immunity against SARS-CoV-2 variants after only a single dose. Together, these findings support further development of our novel and versatile vaccine platform as an alternative or complementary approach to current vaccines.     

Sterile Protection against Plasmodium knowlesi in Rhesus Monkeys from a Malaria Vaccine: Comparison of Heterologous Prime Boost Strategies

Using newer vaccine platforms which have been effective against malaria in rodent models, we tested five immunization regimens against Plasmodium knowlesi in rhesus monkeys. All vaccines included the same four P. knowlesi antigens: the pre-erythrocytic antigens CSP, SSP2, and erythrocytic antigens AMA1, MSP1. We used four vaccine platforms for prime or boost vaccinations: plasmids (DNA), alphavirus replicons (VRP), attenuated adenovirus serotype 5 (Ad), or attenuated poxvirus (Pox). These four platforms combined to produce five different prime/boost vaccine regimens: Pox alone, VRP/Pox, VRP/Ad, Ad/Pox, and DNA/Pox. Five rhesus monkeys were immunized with each regimen, and five Control monkeys received a mock vaccination. The time to complete vaccinations was 420 days. All monkeys were challenged twice with 100 P. knowlesi sporozoites given IV. The first challenge was given 12 days after the last vaccination, and the monkeys receiving the DNA/Pox vaccine were the best protected, with 3/5 monkeys sterilely protected and 1/5 monkeys that self-cured its parasitemia. There was no protection in monkeys that received Pox malaria vaccine alone without previous priming. The second sporozoite challenge was given 4 months after the first. All 4 monkeys that were protected in the first challenge developed malaria in the second challenge. DNA, VRP and Ad5 vaccines all primed monkeys for strong immune responses after the Pox boost. We discuss the high level but short duration of protection in this experiment and the possible benefits of the long interval between prime and boost.     

Supplementation of Influenza Split Vaccines with Conserved M2 Ectodomains Overcomes Strain Specificity and Provides Long-term Cross Protection

Current influenza vaccines do not provide good protection against antigenically different influenza A viruses. As an approach to overcome strain specificity of protection, this study demonstrates significantly improved long-term cross protection by supplementing split vaccines with a conserved molecular target, a repeat of the influenza M2 ectodomain (M2e) expressed on virus-like particles (M2e5x VLPs) in a membrane-anchored form. Intramuscular immunization with H1N1 split vaccine (A/California/07/2009) supplemented with M2e5x VLPs induced M2e-specific humoral and cellular immune responses, and shaped the host responses to the vaccine in the direction of T-helper type 1 responses inducing dominant IgG2a isotype antibodies as well as interferon-γ (IFN-γ) producing cells in systemic and mucosal sites. Upon lethal challenge, M2e5x VLP-supplemented vaccination lowered lung viral loads and induced long-term cross protection against H3N2 or H5N1 subtype influenza viruses over 12 months. M2e antibodies, CD4 T cells, and CD8 T cells were found to contribute to improving heterosubtypic cross protection. In addition, improved cross protection by supplemented vaccination with M2e5x VLPs was mediated via Fc receptors. The results support evidence that supplementation with M2e5x VLPs is a promising approach for overcoming the limitation of strain-specific protection by current influenza vaccination.     

Immunization With a Bivalent Adenovirus-vectored Tuberculosis Vaccine Provides Markedly Improved Protection Over Its Monovalent Counterpart Against Pulmonary Tuberculosis

Recombinant virus-vectored vaccines hold great promise for tuberculosis (TB) vaccination strategies. However, there is a lack of side-by-side comparative investigations to dissect the functional differences and support the advantage of multivalent virus-vectored vaccine over its monovalent counterpart. We previously successfully developed a monovalent adenovirus (Ad)-vectored vaccine expressing Ag85a (AdAg85a) and demonstrated its superior protective efficacy in models of pulmonary TB. In this study, we have developed a bivalent Ad TB vaccine expressing Ag85a and TB10.4 antigens as a fusion protein (AdAg85a:TB10.4) and compared its T-cell–activating and immune protective efficacy with that by monovalent AdAg85a. A single intranasal (i.n.) administration of AdAg85a:TB10.4 induced robust T-cell responses toward the respective antigens within the airway lumen and spleen, although the level of Ag85a-specific T-cell responses in the airway lumen triggered by bivalent AdAg85a:TB10.4 was lower than that by its monovalent counterpart at earlier time points. Thus, a single i.n. delivery of AdAg85a:TB10.4 conferred a markedly improved and sustained level of protection in the lung against Mycobacterium tuberculosis (M.tb)challenge over that by AdAg85a or by conventional BCG immunization with similarly induced levels of protection in the spleen. Our results indicate a unique advantage of multivalent viral-vectored TB vaccines for immunization against pulmonary TB.     

Review of an inactivated vaccine against hantaviruses

OBJECTIVE: Hantaviruses cause haemorrhagic fever with renal syndrome and result in severe morbidity and mortality in humans. Safe and effective vaccines are needed to reduce the incidence of human illness. In this study, the immune response to an inactivated hantavirus vaccine was measured in 64 human volunteers for Hantavax and 10 human volunteers for a Hantaan-Puumala virus combination vaccine at high risk of infection by virtue of their residence and occupation. METHODS: A serum sample was obtained from each volunteer before the initial vaccination (day 0), 30 days after each inoculation and 1 year after the initial dose. All sera were kept at -20 degrees until tested. IgG-specific antibody titres were tested by ELISA and immunofluorescence assay (IFA). Neutralizing antibody titres were determined by a plaque reduction neutralizing test. RESULTS: Thirty days after vaccination, 79 and 62% of the subjects had developed a significant hantavirus antibody titre as measured by IFA and ELISA, respectively. Seroconversion rates increased to 97% 1 month after the booster dose. Neutralizing antibody titres paralleled this trend, with 13% of vaccine recipients producing neutralizing antibody 1 month after the first dose and 75% of vaccine recipients responding 1 month after boosting. Antibody titres had declined by 1 year, however, with only 37 and 43% of sera found to be positive by IFA and ELISA, respectively. Re-vaccination at this time produced a vigorous anamnestic response, with 94 and 100% of vaccine recipients yielding positive antibody titres. Only 50% of the sampled population, however, produced neutralizing antibodies following the booster dose 1 year later. CONCLUSIONS: The vaccine was well tolerated and there were no apparent differences in the responses in human subjects. However, further improvement of this vaccine is necessary in order to induce a longer-lasting humoral immune response.     

Human adenovirus-specific T cells modulate HIV-specific T cell responses to an Ad5-vectored HIV-1 vaccine

Recombinant viruses hold promise as vectors for vaccines to prevent infectious diseases with significant global health impacts. One of their major limitations is that preexisting anti-vector neutralizing antibodies can reduce T cell responses to the insert antigens; however, the impact of vector-specific cellular immunity on subsequent insert-specific T cell responses has not been assessed in humans. Here, we have identified and compared adenovirus-specific and HIV-specific T cell responses in subjects participating in two HIV-1 vaccine trials using a vaccine vectored by adenovirus serotype 5 (Ad5). Higher frequencies of pre-immunization adenovirus-specific CD4⁺ T cells were associated with substantially decreased magnitude of HIV-specific CD4⁺ T cell responses and decreased breadth of HIV-specific CD8⁺ T cell responses in vaccine recipients, independent of type-specific preexisting Ad5-specific neutralizing antibody titers. Further, epitopes recognized by adenovirus-specific T cells were commonly conserved across many adenovirus serotypes, suggesting that cross-reactivity of preexisting adenovirus-specific T cells can extend to adenovirus vectors derived from rare serotypes. These findings provide what we believe to be a new understanding of how preexisting viral immunity may impact the efficacy of vaccines under current evaluation for prevention of HIV, tuberculosis, and malaria.