Safety and immunogenicity of new cell-cultured smallpox vaccine compared with calf-lymph derived vaccine: a blind, single-centre, randomised controlled trial. A novel, cell culture-derived smallpox vaccine in vaccinia-naive adults. Clinical responses to undiluted and diluted smallpox vaccine. Vaccination success rate and reaction profile with diluted and undiluted smallpox vaccine: a randomized controlled trial. Clinical and immunological responses to undiluted and diluted smallpox vaccine with vaccinia virus of Lister strain. Dose-related effects of smallpox vaccine. Response to smallpox vaccine in persons immunized in the distant past. Clonal vaccinia virus grown in cell culture as a new smallpox vaccine. Clinical responses to smallpox vaccine in vaccinia-naive and previously vaccinated populations: undiluted and diluted Lancy-Vaxina vaccine in a single-blind, randomized, prospective trial.
US government organisations have identified the need for a new smallpox vaccine to replenish limited stocks of the approved, calf-lymph derived vaccine, the manufacture of which is no longer acceptable. We aimed to compare the safety and immunogenicity of the new cell-cultured smallpox vaccine (CCSV) to that of the calf-lymph derived vaccine (as a positive control) in 350 healthy, adult volunteers.
                We did a randomised controlled study at the University of Kentucky Medical Center. We randomised 150 vaccinia-naive volunteers, aged 18-30 years, and 100 vaccinia-non-naive people, aged 32-65 years, to equivalent doses of either CCSV or test vaccine (2.5x10(5) plaque-forming units) by 15 puncture scarification in double-blind fashion. Immunogenicity was assessed by pock formation (take rate), humoral immune response by plaque-reduction neutralisation titres, and cellular immune response by vaccinia-specific, interferon-gamma T-cell quantification, cytotoxicity, and T-cell proliferation response. A further 100 vaccine-naive individuals, aged 18-30 years, received one of five doses of CCSV (undiluted, diluted 1 in 5, 1 in 10, 1 in 25, and 1 in 50) in single-blind fashion. Routine laboratory assessments, physical examinations, and recording of adverse events were done to assess vaccine safety. The primary endpoints were safety and reactogenicity (take rate) of CCSV.
                349 (99.7%) of 350 volunteers developed pock lesions; one vaccinia-naive individual who received a 1 in 25 dilution of CCSV did not. The rate of adverse events related to vaccine and the extent of humoral and cellular immune responses did not differ between the vaccine groups in vaccinia-naive or non-naive people. CCSV was immunogenic in vaccine-naive volunteers at a dose 50 times lower than that approved for Dryvax.
                CCSV seems to be a safe and immunogenic alternative to calf-lymph derived vaccine for both vaccinia-naive and non-naive people. Despite the eradication of smallpox as a naturally occurring disease, concern persists over its potential use as a bioterrorist agent. The development of a new-generation smallpox vaccine represents an important contribution to a cogent biodefense strategy. We conducted a phase 2 randomized, double-blind, controlled trial at four sites in the United States to determine whether a clonal smallpox vaccine manufactured in cell culture, ACAM2000, is equivalent to the standard calf-lymph vaccine, Dryvax, in terms of cutaneous response rate, antibody responses and safety. Subjects received either Dryvax or one of four dose levels of ACAM2000 administered percutaneously using a bifurcated needle. All subjects in the highest ACAM2000 dose group and the Dryvax group experienced a successful vaccination. Dilution doses of ACAM2000 were associated with success rates below the 90% threshold established for efficacy. There were no differences in the proportion of subjects who developed neutralizing antibody: 94% in the highest ACAM2000 dose group (95% CI, 84-99) and 96% in the Dryvax group (95% CI, 86-100). No significant differences were seen between the effective ACAM2000 and Dryvax groups regarding the occurrence of adverse events. One subject who received ACAM2000 developed myopericarditis. In healthy, primary vaccines ACAM2000 has a similar vaccination success rate, antibody response, and safety profile to Dryvax. To evaluate the potential to increase the supply of smallpox vaccine (vaccinia virus), we compared the response to vaccination with 10(8.1), 10(7.2), and 10(7.0) plaque-forming units (pfu) of vaccinia virus per milliliter.
                In this randomized, single-blind, prospective study, 680 adults who had not been previously immunized were inoculated intradermally with undiluted vaccine (mean titer, 10(8.1) pfu per milliliter), a 1:5 dilution, or a 1:10 dilution of vaccinia virus with use of a bifurcated needle, and the site was covered with a semipermeable dressing. Subjects were monitored for vesicle formation (an indicator of the success of vaccination) and adverse events for 56 days after immunization.
                Success rates did not differ significantly among the groups and ranged from 97.1 to 99.1 percent after the first vaccination. Both the undiluted and diluted vaccines were reactogenic. In addition to the formation of pustules, common adverse events included the formation of satellite lesions, regional lymphadenopathy, fever, headache, nausea, muscle aches, fatigue, and chills consistent with the presence of an acute viral illness. Generalized and localized rashes, including two cases of erythema multiforme, were also observed.
                When given by a bifurcated needle, vaccinia virus vaccine can be diluted to a titer as low as 10(7.0) pfu per milliliter (approximately 10,000 pfu per dose) and induce local viral replication and vesicle formation in more than 97 percent of persons. Additional smallpox vaccine doses are needed to augment current US national stockpile. Aventis Pasteur smallpox vaccine (APSV), initially manufactured in the 1950s from the New York Board of Health vaccinia strain in a frozen preparation, appears as effective as lyophilized vaccine but the effectiveness of diluted doses of APSV is unclear.
                To compare the vaccination success rate and the reaction profile of various APSV dilutions.
                A double-blind, randomized controlled trial of 340 healthy vaccinia-naive adults aged 18 to 32 years from 3 academic medical centers who were vaccinated with 1 of 3 strengths of APSV dilutions (undiluted, 1:5, and 1:10) between October 9, 2002, and February 24, 2003. Volunteers were followed up every 3 to 5 days until the vaccination site healed for bandage changes, vaccine response assessment, and adverse event evaluation, followed by 1- and 2-month clinic evaluations and 6-month telephone interview.
                Successful vaccination, defined by presence of a vesicle or pustule at the inoculation site 6 to 11 days postvaccination, and local and systemic reactions to vaccination.
                A total of 340 volunteers were vaccinated (vaccine dose: undiluted, n = 113; 1:5 dilution, n = 114; and 1:10 dilution, n = 113). Following vaccination, 99.4% (95% confidence interval [CI], 97.9%-99.9%) of all volunteers had successful vaccinations. Success rates did not differ between the dilution groups (undiluted, 100.0%; 95% CI, 96.8%-100.0%; 1:5 dilution, 98.2%; 95% CI, 93.8%-99.8%; 1:10 dilution, 100.0% 95% CI, 96.8%-100.0%; P =.33). Overall, 99.7% of volunteers reported at least 1 local symptom at the vaccination site, and 61.8% had axillary lymphadenopathy, 15.0% developed satellite lesions, and 7.6% developed a rash away from the vaccination site. Fever developed in 21.5%. No differences were noted in local or systemic reactions between the 3 dilution groups (P>.05 for each comparison). A total of 25% of volunteers missed scheduled duties due to vaccine-related symptoms.
                Even at diluted doses, APSV is an effective smallpox vaccine, allowing for expansion of the current stockpile. However, reactogenicity was not reduced with dilution of the vaccine and, as with other smallpox vaccines, may impair daily activities. The potential to increase the supply of vaccine by diluting the vaccinia virus of Lister strain to face possible bioterrorism with smallpox was evaluated. Vaccinia-naïve subjects (n=97) were randomized to receive either undiluted or diluted (1:5, 1:10) vaccine, and previously vaccinated subjects (n=122) were randomized to receive either undiluted or diluted (1:10, 1:30) vaccine. Except two subjects who received 1:30 diluted vaccine, the vaccination of all subjects was successful clinically. All subjects had significant vaccinia-specific T cell and antibody responses. The diluted vaccine was not associated with decreased local or systemic reactions, lower T cell responses, or higher antibody titers when compared with undiluted vaccine. Here we show the diluted vaccine of Lister strain can be used in vaccinia-naïve subjects and previously vaccinated subjects if viral titer > or =10(8) and 10(7.5) pfu/mL after dilution, respectively. The reactogenicity of vaccinia virus may not be a dose-dependent response. 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-gamma-producing T cells.
                Sixty healthy adults were inoculated intradermally by bifurcated needle with undiluted vaccine (dose, 10(7.8) plaque-forming units [pfu] per milliliter), a 1:10 dilution (dose, 10(6.5) pfu per milliliter), or a 1:100 dilution (dose, 10(5.0) 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.
                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-gamma responses occurred in 94 percent of subjects with vesicles, and a cytotoxic T-cell response occurred in only one subject without a vesicle.
                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. There is renewed interest in use of smallpox vaccine due to the potential for a bioterrorist attack. This would involve vaccinating health care workers who were previously vaccinated.
                To evaluate the use of diluted vaccinia virus in vaccination of previously vaccinated (non-naive) participants.
                Eighty non-naive participants, aged 32 to 60 years, were randomized in a single-blinded study to receive either undiluted or diluted (1:3.2, 1:10, or 1:32) doses of smallpox vaccine. A comparison group, aged 18 to 31 years, of 10 vaccinia-naive participants received undiluted vaccine. Participants were enrolled between April 1 and May 15, 2002, at the National Institute of Allergy and Infectious Diseases Vaccine and Treatment Evaluation Unit at Saint Louis University, St Louis, Mo.
                Smallpox vaccine was administered by scarification using 15 skin punctures in the deltoid region of the arm.
                Presence of a major reaction, defined as a vesicular or pustular lesion or area of palpable induration surrounding a central lesion following vaccination, and measures of viral shedding and antibody titers.
                Initial vaccination resulted in a major reaction in 64 of 80 non-naive participants. Ninety-five percent of non-naive participants had major reactions in the undiluted group, 90% in the 1:3.2 dilution group, 81% in the 1:10 dilution group, and 52.6% in the 1:32 dilution group. All (n = 10) of the vaccinia-naive participants had major reactions. Compared with vaccinia-naive participants, non-naive participants had significantly smaller skin lesions (P =.04) and significantly less incidence of fever (P =.02). Preexisting antibody was present in 76 of 80 non-naive participants. Antibody responses were significantly higher and occurred more rapidly in the non-naive participants compared with the vaccinia-naive participants (P =.002 for day 28 and P =.003 for 6 months). Vaccinia-naive participants shed virus from the vaccination site 2 to 6 days longer and had significantly higher peak mean viral titers when compared with the non-naive participants (P =.002).
                Previously vaccinated persons can be successfully revaccinated with diluted (<or=1:10) smallpox vaccine. Fewer adverse reactions were observed in this study of non-naive participants when compared with events in vaccinia-naive participants, which may be due to immunologic memory. Although the smallpox virus was eradicated over 20 years ago, its potential release through bioterrorism has generated renewed interest in vaccination. To develop a modern smallpox vaccine, we have adapted vaccinia virus that was derived from the existing Dryvax vaccine for growth in a human diploid cell line. We characterized six cloned and one uncloned vaccine candidates. One clone, designated ACAM1000, was chosen for development based on its comparability to Dryvax when tested in mice, rabbits and monkeys for virulence and immunogenicity. By most measures, ACAM1000 was less virulent than Dryvax. We compared ACAM1000 and Dryvax in a randomized, double-blind human clinical study. The vaccines were equivalent in their ability to produce major cutaneous reactions ('takes') and to induce neutralizing antibody and cell-mediated immunity against vaccinia virus. We conducted a single-blind, randomized trial of 2 dilutions (1:1 or 1:10) of Lancy-Vaxina vaccine (Berna Biotech) in vaccinia-naive persons (n=36) and persons previously vaccinated >25 years ago (n=76). All vaccinees responded successfully to the vaccination. There were no significant differences in the size of the skin lesions, the number of adverse events, the amount of viral shedding, or the level of antibody responses between the undiluted (n=56) and diluted (n = 56) vaccine groups. Compared with vaccinia-naive persons, previously vaccinated persons exhibited significantly smaller and more rapidly evolving skin lesions and fewer adverse events. Previously vaccinated persons had significantly higher neutralizing antibody levels before the administration of the study vaccine than vaccinia-naive persons, and viral shedding from lesions in previously vaccinated persons was lower and diminished more rapidly than from lesions in vaccinia-naive persons.
The evidence shows that stockpiled vaccines have maintained their immunogenicity and new cell-cultured vaccines are similar to stockpiled vaccines in terms of vaccination success rate and immunogenicity. First- and second-generation vaccines diluted to at least 1:10 are as effective as undiluted vaccine in terms of clinical success rate and immunogenicity. Dilution did not reduce the frequency of adverse events. Success rate and immunogenicity were similar in naive and previously vaccinated persons, but there were fewer adverse events in previously vaccinated persons. The rate of adverse events found in this review reveals the need for further development and improvement of smallpox vaccines.