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Background: Previously, our group conducted the Herpevac Trial for Women, a randomized efficacy field trial of type 2 glycoprotein D (gD2) herpes simplex virus (HSV) vaccine adjuvanted with ASO4 in 8323 women. Study participants were selected to be seronegative for HSV-1 and HSV-2. We found that the vaccine was 82% protective against culture-positive HSV-1 genital disease but offered no significant protection against HSV-2 genital disease. Efficacy against HSV-1 was associated with higher levels of antibody to gD2 at enzyme-linked immunosorbent assay (ELISA)., Methods: To better understand the results of the efficacy study, we measured postvaccination concentrations of neutralizing antibody (nAb) to either HSV-1 and HSV-2 from HSV-infected study participants and matched uninfected controls. Statistical modeling was used to determine whether these responses were correlated with protection against HSV., Results: nAbs to either HSV-1 or HSV-2 were correlated with ELISA binding antibodies to gD2. HSV-1 or HSV-2 nAb findings support the observation of protection by higher levels of antibody against HSV-1 infection, but the lack of protection against HSV-2 remains unexplained., Conclusions: The protection against HSV-1 infection observed in the Herpevac Trial for Women was associated with nAbs directed against the virus, although the power to assess this was lower in the nAb study compared with the ELISA results owing to smaller sample size., Clinical Trials Registration: NCT00057330., Competing Interests: Potential conflicts of interest. R. B. B. serves on data and safety monitoring committees for Pfizer, GSK, Merck, Sanofi and the National Institute of Allergy and Infectious Diseases and is a consultant to XVax, Meissa and Vaxart. All other authors report no potential conflicts. The author has submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2022. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: The glycoprotein D (gD)/AS04 vaccine failed to prevent herpes simplex virus (HSV) 2 in clinical trials. Failure was recapitulated in mice, in which the vaccine elicited neutralizing antibody but not antibody-dependent cell-mediated cytotoxicity (ADCC) responses. Preclinical findings suggest that ADCC is important for protection, but the clinical data are limited. We hypothesized that gD/AS04 and acute HSV-2 infection elicit primarily neutralizing antibodies, whereas ADCC emerges over time., Methods: HSV-specific immunoglobulin G, subclass, function (neutralization, C1q binding and ADCC), and antigenic targets were compared (paired t test or Mann-Whitney U test) at enrollment and after gD/AS04 vaccination, before and after HSV-2 acquisition in vaccine controls, and in an independent cohort with chronic HSV-2 infection., Results: Vaccination elicited only a neutralizing antibody response, whereas acute infection elicited neutralizing and C1q-binding antibodies but not a significant ADCC response. Antibodies to gD were exclusively immunoglobulin G1 and only neutralizing. In contrast, women with chronic HSV-2 infection had significantly greater ADCC responses and targeted a broader range of viral antigens compared with acutely infected or gD/AS04 vaccine recipients (P < .001)., Conclusions: Results from gD/AS04 vaccinated or acutely infected women recapitulate murine findings of limited functional antibody responses, supporting the speculation that vaccines that generate polyfunctional and specifically ADCC responses may be required to prevent HSV-2 acquisition and limit recurrences., Competing Interests: Potential conflicts of interest. R. B. B. serves on data and safety monitoring committees for Pfizer, GSK, Merck, Sanofi, and the National Institute of Allergy and Infectious Diseases and is a consultant to X-Vax, Meissa and Vaxart. B. C. H. receives support for development of the single-cycle candidate vaccine deleted in HSV-2 glycoprotein D (ΔgD-2) from X-Vax Technology, which holds the license for its development, and serves as a scientific advisor for the company. B. C. H. is an inventor on a patent for the ΔgD-2 vaccine. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2022. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Unlabelled: Although effective hepatitis C virus (HCV) antivirals are on the horizon, a global prophylactic vaccine for HCV remains elusive. The diversity of the virus is a major concern for vaccine development; there are 7 major genotypes of HCV found globally. Therefore, a successful vaccine will need to protect against HCV infection by all genotypes. Despite the diversity, many monoclonal antibodies (MAbs) with broadly cross-neutralizing activity have been described, suggesting the presence of conserved epitopes that can be targeted to prevent infection. Similarly, a vaccine comprising recombinant envelope glycoproteins (rE1E2) derived from the genotype 1a HCV-1 strain has been shown to be capable of eliciting cross-neutralizing antibodies in guinea pigs, chimpanzees, and healthy human volunteers. In order to investigate the basis for this cross-neutralization, epitope mapping of anti-E1E2 antibodies present within antisera from goats and humans immunized with HCV-1 rE1E2 was conducted through peptide mapping and competition studies with a panel of cross-neutralizing MAbs targeting various epitopes within E1E2. The immunized-goat antiserum was shown to compete with the binding of all MAbs tested (AP33, HC33.4, HC84.26, 1:7, AR3B, AR4A, AR5A, IGH526, and A4). Antisera showed the best competition against HC84.26 and AR3B and the weakest competition against AR4A. Furthermore, antisera from five immunized human vaccinees were shown to compete with five preselected MAbs (AP33, AR3B, AR4A, AR5A, and IGH526). These data show that immunization with HCV-1 rE1E2 elicits antibodies targeting multiple cross-neutralizing epitopes. Our results further support the use of such a vaccine antigen to induce cross-genotype neutralization., Importance: An effective prophylactic vaccine for HCV is needed for optimal control of the disease burden. The high diversity of HCV has posed a challenge for developing vaccines that elicit neutralizing antibodies for protection against infection. Despite this, we have previously shown that a vaccine comprising recombinant envelope glycoproteins derived from a single genotype 1a strain was capable of eliciting a cross-neutralizing antibody response in human volunteers. Here, we have used competition binding assays and peptide binding assays to show that antibodies present in the antisera from vaccinated goats and humans bind epitopes overlapping with those of a variety of well-characterized cross-neutralizing monoclonal antibodies. This provides a mechanism for the cross-neutralizing human antisera: antibodies present in the antisera bind to conserved regions associated with cross-neutralization. Importantly, this work provides further support for a vaccine comprising recombinant envelope glycoproteins, perhaps in a formulation with a vaccine component eliciting strong anti-HCV CD4(+) and CD8(+) T cell responses., (Copyright © 2014, American Society for Microbiology. All Rights Reserved.)

The Herpevac Trial evaluated a herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) subunit vaccine to prevent genital herpes. Unexpectedly, the vaccine protected against genital HSV-1 infection but not genital HSV-2 infection. We evaluated sera from 30 women seronegative for HSV-1 and HSV-2 who were immunized with gD2 in the Herpevac Trial. Neutralizing antibody titers to HSV-1 were 3.5-fold higher than those to HSV-2 (P < .001). HSV-2 gC2 and gE2 on the virus blocked neutralization by gD2 antibody, while HSV-1 gC1 and gE1 did not block neutralization by gD2 antibody. The higher neutralizing antibody titers to HSV-1 offer an explanation for the Herpevac results, and shielding neutralizing domains provides a potential mechanism., (© The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Background: This study examined the transmissibility between young children of an intranasally administered live attenuated human parainfluenza virus type 3 (HPIV3)-cp45 vaccine candidate., Methods: Eighty subjects were enrolled in playgroups among whom there was at least one infected vaccinee in close contact with a seronegative placebo recipient over 21 days without a confounding infection with wtHPIV3. Following vaccination viral cultures were obtained on nine occasions to detect shedding and transmission of HPIV3cp45. Serum antibody titers were measured before and 7 weeks after vaccination., Results: No child fulfilled the criteria for transmission of HPIV3cp45 giving a risk of transmission of 0.04 (95% CI 0.01-0.19), hence establishing that HPIV3cp45 is less infectious than wtHPIV3 and risk of transmission is not a limitation to further clinical development of this vaccine candidate.

A phase 2 evaluation of live attenuated parainfluenza type 3 (PIV3)-cold passage mutant 45 (cp45) vaccine was conducted in 380 children 6-18 months old; 226 children (59%) were seronegative for PIV3. Of the 226 seronegative children, 114 received PIV3-cp45 vaccine, and 112 received placebo. No significant difference in the occurrence of adverse events (i.e., runny nose, cough, or temperature > or =38 degrees C) was noted during the 14 days after vaccination. There was no difference between groups in the occurrence of acute otitis media or serous otitis media. Paired serum samples were available for 109 of the seronegative vaccine recipients and for 110 of the seronegative placebo recipients; 84% of seronegative vaccine recipients developed a > or =4-fold increase in antibody titers. The geometric mean antibody titer after vaccination was 1 : 25 in the vaccine group and <1 : 4 in the placebo group. PIV3-cp45 vaccine was safe and immunogenic in seronegative children and should be evaluated for efficacy in a phase 3 field trial.

Background: Parainfluenza type 3 virus (PIV-3) infections cause lower respiratory tract illness in children throughout the world. A licensed PIV-3 vaccine is not yet available., Methods: A live attenuated cold-adapted (ca) and temperature-sensitive (ts) PIV-3 vaccine, designated cp-45, was evaluated sequentially in open label studies in 20 adults and in placebo-controlled, double blind studies in 24 PIV-3-seropositive children, 52 PIV-3-seronegative infants and children and 49 infants 1 to 2 months old. A single dose of this intranasal vaccine was evaluated in adults [106 plaque-forming units (pfu)] and seropositive children, and 104 and 105 pfu were evaluated in seronegative children. In the infant study, two 104 pfu doses of vaccine were administered at 1- or 3-month intervals. Safety, infectivity, immunogenicity and phenotypic stability of the vaccine were evaluated in all cohorts., Results: The cp-45 vaccine was well-tolerated in all age groups and infected 94% of vaccinated seronegative children and 94% of vaccinated infants. Although immunization with the first dose of cp-45 diminished the replication of a second dose in all infants, those immunized after 3 months shed vaccine virus more frequently than those immunized after 1 month (62% vs. 24%, respectively). Antibody responses to PIV-3 were readily detected in seronegative children with a variety of assays; however, the IgA response to the viral hemagglutinin-neuraminidase was the best measure of immunogenicity in young infants. Of 109 vaccine virus specimens recovered from nasal washes, 98 were ts and 11 were temperature-sensitive intermediate (tsi) viruses, with pinpoint plaques visible at 40 degrees C. tsi viruses appeared transiently at the time of peak viral replication, represented a very small proportion of the total virus shed and were not associated with changes in clinical status. ca revertants were not detected., Conclusions: The cp-45 vaccine is appropriately attenuated and immunogenic in infants as young as 1 month of age. Further development of this vaccine is warranted.

Preventive viral vaccine efficacy trials require large-scale sample analysis to quantitate immune responses and their correlation with infection outcomes. Traditional plaque reduction assays measure a functionally important form of humoral immunity, neutralizing antibody titer. These assays, however, are time-consuming and laborious. We previously developed a higher throughput assay of neutralizing antibody to herpes simplex viruses 1 and 2 (Blevins et al., PLOS ONE, 10(12), e0144738) using the enzyme-linked virus inducible system (ELVIS) cell line; this cell line produces β-galactosidase in response to HSV infection. Here, serum samples from recipients of an investigational vaccine in the Herpevac Trial for Women were used to compare the ELVIS cell assay with the lower throughput, traditional plaque reduction assay. We demonstrate that neutralizing antibody titers to HSV-1 or HSV-2 determined using ELVIS cells positively correlate with neutralizing antibody titers determined by traditional plaque reduction assay, thus validating a higher throughput alternative for large-scale sample analysis. [ABSTRACT FROM AUTHOR]

The Herpevac Trial for Women revealed that three dose HSV-2 gD vaccine was 58% protective against culture-positive HSV-1 genital disease, but it was not protective against HSV-2 infection or disease. To determine whether vaccine-induced immune responses had selected for a particular gD sequence in strains infecting vaccine recipients compared with viruses infecting control subjects, genetic sequencing studies were carried out on viruses isolated from subjects infected with HSV-1 or HSV-2. We identified naturally occurring variants among the gD sequences obtained from 83 infected subjects. Unique or low frequency amino acid substitutions in the ectodomain of gD were found in 6 of 39 HSV-1-infected subjects and in 7 of 44 HSV-2-infected subjects. However, no consistent amino acid change was identified in isolates from gD-2 vaccine recipients compared with infected placebo recipients. gC and gE surround and partially shield gD from neutralizing antibody, and gB also participates closely in the viral entry process. Therefore, these genes were sequenced from a number of isolates to assess whether sequence variation may alter protein conformation and influence the virus strain’s capacity to be neutralized by vaccine-induced antibody. gC and gE genes sequenced from HSV-1-infected subjects showed more variability than their HSV-2 counterparts. The gB sequences of HSV-1 oral isolates resembled each other more than they did gB sequences rom genital isolates. Overall, however, comparison of glycoprotein sequences of viral isolates obtained from infected subjects did not reveal any singular selective pressure on the viral cell attachment protein or surrounding glycoproteins due to administration of gD-2 vaccine. [ABSTRACT FROM AUTHOR]

Although a cure for HCV is on the near horizon, emerging drug cocktails will be expensive, associated with side-effects and resistance making a global vaccine an urgent priority given the estimated high incidence of infection around the world. Due to the highly heterogeneous nature of HCV, an effective HCV vaccine which could elicit broadly cross-neutralizing antibodies has represented a major challenge. In this study, we tested for the presence of cross-neutralizing antibodies in human volunteers who were immunized with recombinant glycoproteins gpE1/gpE2 derived from a single HCV strain (HCV1 of genotype 1a). Cross neutralization was tested in Huh-7.5 human hepatoma cell cultures using infectious recombinant HCV (HCVcc) expressing structural proteins of heterologous HCV strains from all known major genotypes, 1–7. Vaccination induced significant neutralizing antibodies against heterologous HCV genotype 1a virus which represents the most common genotype in North America. Of the 16 vaccinees tested, 3 were selected on the basis of strong 1a virus neutralization for testing of broad cross-neutralizing responses. At least 1 vaccinee was shown to elicit broad cross-neutralization against all HCV genotypes. Although observed in only a minority of vaccinees, our results prove the key concept that a vaccine derived from a single strain of HCV can elicit broad cross-neutralizing antibodies against all known major genotypes of HCV and provide considerable encouragement for the further development of a human vaccine against this common, global pathogen. [ABSTRACT FROM AUTHOR]

We hypothesized that individuals who develop fever after smallpox vaccination have genetically determined differences in their immune responses to vaccinia virus. We looked for an association between the development of fever and single-nucleotide polymorphisms (SNPs) in 19 candidate genes in 346 individuals previously assessed for clinical responses to smallpox vaccination. Fever after smallpox vaccination is associated with specific haplotypes in the interleukin (IL)-1 gene complex and in the IL18 gene. A haplotype in the IL4 gene was highly significant for reduced susceptibility to the development of fever after vaccination among vaccinianaive individuals. Our results indicate that certain haplotypes in the IL-1 gene complex and in IL18 and IL4 predict an altered likelihood of the development of fever after smallpox vaccination. Our findings also raise the possibility that these same haplotypes may identify individuals at risk for the development of fever after receipt of other live virus vaccines, providing information that could be useful in anticipating and preventing more-serious adverse events. [ABSTRACT FROM AUTHOR]

Inactivated poliovirus vaccine (IPV) is believed to induce significantly lower mucosal immunity than oral poliovirus vaccine (OPV). Most of the data supporting this were generated before enhanced IPV (eIPV) was introduced. Excretion of poliovirus by OPV recipients can be used to assess intestinal immunity. We studied polymerase chain reaction amplification of viral complementary DNA from the stool of children vaccinated with either OPV alone or eIPV. Of first-time OPV recipients, 92% excreted virus after 1 week, and 81% excreted virus after 3 weeks. Prior vaccination with OPV reduced the number to 22% and shortened the duration of virus excretion (to 5% after 3 weeks). Two doses of IPV reduced the number of poliovirus-positive 1-week samples (to 76%), the duration of shedding (to 37% at 3 weeks), and the quantity of excreted virus. This suggests that IPV-vaccinated communities are partially protected from the spread of poliovirus. Further enhancement of IPV potency may lead to even higher levels of mucosal immunity. [ABSTRACT FROM AUTHOR]

The efficacy and effectiveness of cold adapted live attenuated (CAIV-T, FluMist®) intranasal influenza vaccine is reviewed. CAIV-T consists of approximately 107 TCID50 per dose of each influenza A/H1N1, influenza A/H3N2, and influenza B vaccine strain. The exact strains are updated each year to antigenically match the antigens recommended by national health authorities for inclusion in the vaccine. In one year in which the vaccine strain did not well match the epidemic strain, the live attenuated vaccine induced a broad immune response that cross-reacted significantly with the drifted strain. The efficacy of CAIV-T in adults was demonstrated with challenge studies and the effectiveness of the vaccine for reducing febrile upper respiratory illness, days of missed work, and days of antibiotic use was demonstrated in a large field trial. In young children, protective efficacy against culture confirmed influenza was demonstrated in a field trial with overall protective efficacy of 92% during a two year study. Vaccine was also highly protective against a strain not contained in the vaccine, with 86% protective efficacy demonstrated against this significantly drifted virus. Effectiveness measures, including protection against febrile otitis media and visits to the doctor were demonstrated. Live attenuated vaccine provides a significant new tool to help prevent influenza. [Copyright &y& Elsevier]

Examines the stability of Dryvax virus vaccine to determine whether diluted vaccine could be used over an extended period, thereby increasing the number of available doses. Stability parameters; Dilution; Diluent; Temperature; Effects of storage of reconstituted Dryvax vaccine at room temperature, regardless of dilution or diluent.

Induction of human γδ T cells was investigated in subjects who were vaccinated with live recombinant canarypox virus expressing human immunodeficiency virus (HIV) proteins or soluble MN rgp120. Both canarypox and rgp120 induced antigen-specific lymphoproliferative and interferon (IFN)—γ responses. However, only canarypox vaccination induced increased γδ T cell responses detectable after secondary in vitro expansion (P < .02). These enhanced γδ T cell responses were specific for canarypox but not HIV antigens. Canarypox-specific γδ T cells were predominantly Vγ9[sub +] and produced intracellular and secreted IFN-γ. γδ T cell lines generated from canarypox vaccinees responded to canarypox antigens but not to mycobacterial antigens shown previously to induce bacille Calmette-Guérin—specific γδ T cells. Furthermore, canarypox vaccinations were associated with significantly higher NK cell expansions (P = .02). Increased IFN—γ production by γδ T and NK cells could enhance the induction of protective type 1 memory immunity. Thus, stimulation of γδ T cells might be an important feature of live vaccines. [ABSTRACT FROM AUTHOR]

Reports on the effectiveness of live, attenuated influenza virus (LAIV) vaccines and the economic and medical implications. Objective; Design; Setting; Participants; Intervention; Main outcome measures; Results; Conclusion.

Background Demonstration of protection by a M2SR (M2 deficient Single Replication) monovalent H3N2 vaccine was assessed in a phase 2a clinical trial in which the challenge virus was substantially drifted from the vaccine. M2SR is an investigational, live virus vaccine containing hemagglutinin (HA) and neuraminidase (NA) selected from targeted Type A influenza strains. M2SR undergoes only a single round of infection in the respiratory epithelium but evokes an immune response profile similar to wild-type influenza virus and protects ferrets against both homologous and heterologous influenza variants. Methods A blinded, randomized, placebo-controlled human challenge study (EudraCT #: 2017-004971-30) was conducted with M2SR containing HA and NA from A/Brisbane/10/2007 (H3N2). 18–55-year-old subjects received 1 IN dose of saline or 108 TCID50 of vaccine. 4 weeks later, 99 subjects were challenged IN with 106 TCID50 H3N2 A/Belgium/4217/2015 (Figures 1 and 2). Results Adverse events (AE) were similar between placebo (N = 51) and M2SR recipients (N = 48) during the 28 days after immunization. After challenge with A/Belgium/4217/2015, 35% of M2SR recipients experienced influenza infection and illness, compared with 49% of placebo subjects (Figure 3). An 18% reduction in viral load was noted after challenge for M2SR subjects. Serum microneutralization response to vaccine was detected in 54% of M2SR subjects (vs. 0/51 placebo subjects), and among these subjects a 34% reduction in viral load and 51% reduction in symptom scores was noted after challenge vs placebo. Among the 29% of subjects with post-vaccine response to both vaccine and challenge strains, a 62% reduction in viral load and 56% reduction in symptom scores was noted after challenge with highly drifted H3N2 (Figure 4). Conclusion One dose of M2SR protected healthy adults against influenza infection and illness with a highly drifted challenge strain. This is believed to be the first study to demonstrate protection against challenge with an influenza strain substantially different from the vaccine and indicates potential for improved breadth of protection by M2SR compared with current vaccines. The mild vaccine AE profile supports clinical trials of additional dose levels and regimens to enhance drifted strain protection by M2SR. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]

Presents letters to the editor related to HIV clinical trials. Information on the phase III trial initiated in Thailand; Plan by the U.S. National Institute of Health, regarding vaccine trials.

Background During the 2009 influenza pandemic both seasonal and 2009 pandemic vaccines were recommended. We conducted a randomized trial of monovalent 2009-H1N1 vaccine and seasonal trivalent inactivated influenza vaccine (IIV3) given sequentially or concurrently to adults. Methods Adults randomized to 4 study groups and stratified by age (18–64 and ≥65 years) received 1 dose of seasonal IIV3 or placebo and 2 doses of 2009-H1N1 vaccine or placebo in one of 4 combinations, i.e., H1N1 + Placebo/H1N1 + Placebo/ II V 3 (HP/HP/ V3 ), H1N1 + IIV3 /H1N1 + Placebo/Placebo (H V3 /HP/P), H1N1 + Placebo/H1N1 + IIV3 /Placebo (HP/H V3 /P), and IIV3 + Placebo/H1N1 + Placebo/H1N1 ( V3 P/HP/H). Intramuscular injections were given three times at 21 day intervals. Sera for antibody assays were obtained prior to and 21 days after each vaccination. Reactogenicity and adverse events were monitored. Results Eight hundred-five (805) adults were enrolled. All combinations of vaccines were safe and well tolerated. In general, one dose of 2009-H1N1 and one dose of IIV3, regardless of sequence or concurrency of administration, were immunogenic in adults. There were no significant differences in geometric mean titers (GMT) or the proportions of subjects with ≥4-fold rise in antibody responses and titers ≥40 for any vaccine group or between age strata for 2009-H1N1 after the first or second dose, although the vaccine sequence affected the titers to the IIV3 antigens. Hemagglutination inhibition antibody (HAI) GMTs against 2009-H1N1 for the combined age strata 21 days after the first 2009-H1N1 dose were 190.4, 182.1, 232.9 and 157.5 for HP/HP/ V3 , H V3 /HP/P, HP/H V3 /P and V3 P/HP/H, respectively. While IIV3 GMTs were adequate they were generally lower than the 2009-H1N1 GMTs. In a subset of subjects, there was good correlation between HAI and microneutralization (MN) titers (Spearman's correlation coefficient 0.92). Conclusions All vaccine combinations were generally well tolerated. Immune responses to one dose of 2009-H1N1 were adequate regardless of the sequence of vaccination in all age groups, but the sequence affected titers to IIV3 antigens. [ABSTRACT FROM AUTHOR]

Abstract: A total of 600 healthy adults ≥65 years were randomized to receive 2 vaccinations 1 month apart of a subvirion avian influenza A/H5N1 vaccine containing 3.75, 7.5, 15, or 45μg of hemagglutinin (HA) with or without aluminum hydroxide (AlOH). All formulations were safe. Groups given the vaccine with AlOH had more injection site discomfort. Dose-related increases in antibody responses were noted after the second vaccination. Antibody responses to the vaccine were not enhanced by AlOH at any HA dose level. A microneutralization titer ≥40 was observed in 36% and 40% of subjects who received 45μg of HA with or without AlOH, respectively. [Copyright &y& Elsevier]

Background: We conducted a double-blind, randomized trial of three dilutions of vaccinia virus vaccine in previously unimmunized adults in order to assess the clinical success rates, humoral responses, and virus-specific activity of cytotoxic T cells and interferon-γ–producing T cells. Methods: Sixty healthy adults were inoculated intradermally by bifurcated needle with undiluted vaccine (dose, 107.8 plaque-forming units [pfu] per milliliter), a 1:10 dilution (dose, 106.5 pfu per milliliter), or a 1:100 dilution (dose, 105.0 pfu per milliliter); there were 20 subjects in each group. The subjects were monitored with respect to vesicle formation (an indicator of successful vaccination), the viral titer at the time of peak lesion formation, antiviral antibodies, and cellular immune responses. Results: A vaccinia vesicle developed in 19 of the 20 subjects who received undiluted vaccine (95 percent), 14 of the 20 who received the 1:10 dilution (70 percent), and 3 of the 20 who received the 1:100 dilution (15 percent). One month after vaccination, 34 of 36 subjects with vesicles had antibody responses, as compared with only 1 of 24 subjects without clinical evidence of vaccinia virus replication. Vigorous cytotoxic T-cell and interferon-γ responses occurred in 94 percent of subjects with vesicles, and a cytotoxic T-cell response occurred in only one subject without a vesicle. Conclusions: The vaccinia virus vaccine (which was produced in 1982 or earlier) still has substantial potency when administered by a bifurcated needle to previously unvaccinated adults. Diluting the vaccine reduces the rate of successful vaccination. The development of vesicular skin lesions after vaccination correlates with the induction of the antibody and T-cell responses that are considered essential for clearing vaccinia virus infections. (N Engl J Med 2002;346:1275-80.) [ABSTRACT FROM AUTHOR]