Showing papers on "Vaccination published in 1981"

Persistence of neutralizing antibody 30-35 years after immunization with 17D yellow fever vaccine

Abstract: Previous studies on the duration of antibody following vaccination with 17D yellow fever (17D YF) virus vaccine have indicated that immunity persists for at least 17 years and suggest that the vaccine may provide lifelong immunity. We studied sera obtained from 149 veterans of the Second World War, 30 - 35 years after military service during which YF vaccination was required for defined groups. A significantly high proportion of "vaccinated" subjects was found to be seropositive to 17D YF virus. The highest proportion of seropositive "vaccinated" veterans (97%) was among navy and air corps personnel, while only 60% of "vaccinated" army personnel and 19% of "unvaccinated" personnel were seropositive. This study suggests that (i) antibody to 17D YF virus, as measured by the plaque-reduction neutralization test (PRNT), persists for 30 years or more following administration of a potent vaccine; (ii) army personnel often had not received potent vaccine, even though their service history indicated that they should have been vaccinated; (iii) some personnel were vaccinated, although their service did not include vaccination-designated areas; and (iv) 88% of veterans with persistent PRNT antibody to 17D YF virus also had mouse-protective antibody against French neurotropic YF virus.

Pertussis immunisation and serious acute neurological illness in children

Abstract: OBJECTIVE--To determine long term outcome in children who had a severe acute neurological illness in early childhood associated with pertussis immunisation. DESIGN--Follow up study of cases and matched controls. SETTING--Assessment of children at home and at school throughout Britain. SUBJECTS--Children recruited into the national childhood encephalopathy study in 1976-9 were followed up, with one of their two original matched controls, in 1986-9. MAIN OUTCOME MEASURES--Performance in educational attainment tests; behaviour problems reported by teachers and parents; continuing convulsions; evidence of other neurological or physical dysfunction. RESULTS--Over 80% of cases and controls were traced. Case children were significantly more likely than controls to have died or to have some form of educational, behavioural, neurological, or physical dysfunction a decade after their illness. The prevalence of one or more of these adverse outcomes in case children who had been immunised with diphtheria, tetanus, and pertussis vaccine within seven days before onset of their original illness was similar to that in case children who had not been immunised recently. The relative risk for recent diphtheria, tetanus, and pertussis immunisation in children who had died or had any dysfunction in comparison with controls was 5.5 (95% confidence interval 1.6 to 23.7). However, the number of cases associated with vaccine (12) was extremely small and statistically vulnerable, and other possible agents or predisposing factors could not be excluded. CONCLUSIONS--Diphtheria, tetanus, and pertussis vaccine may on rare occasions be associated with the development of severe acute neurological illnesses that can have serious sequelae. Some cases may occur by chance or have other causes. The role of pertussis vaccine as a prime or concomitant factor in the aetiology of these illnesses cannot be determined in any individual case. The balance of possible risk against known benefits from pertussis immunisation supports continued use of the vaccine.

Assessment of the Antibody Response to Pneumococcal Vaccine in High-Risk Populations

Abstract: Vaccine-induced levels of antibody to Streptococcus pneumoniae of approximately 250-300 ng of antibody nitrogen/ml are protective against pneumococcal disease. Side effects of vaccination are not severe and are generally confined to local reactions at the site of inoculation. Patients with a documented high risk of acquiring pneumococcal disease include the elderly, especially those with underlying cardiopulmonary disease, and those with sickle cell anemia, Hodgkin's disease, a renal transplant, multiple myeloma, asplenia, and nephrotic syndrome. People with insulin-dependent diabetes mellitus or renal failure do not appear to be at high risk. All of these groups, except those with multiple myeloma, respond to vaccine with levels of antibody that are protective for many but not all of the serotypes included in the vaccine. Immunosuppression, splenectomy, and hemoglobinopathy depress antibody response. Duration of vaccine-induced antibody is unknown but may be shorter than that in normal persons. Preliminary guidelines for vaccination are proposed.

Guillain-Barre syndrome and the 1978-1979 influenza vaccine.

Abstract: An ongoing surveillance program was intensified to determine whether an increased risk of acquiring vaccine-related Guillain-Barre syndrome (GBS) (similar to that observed after vaccination with the A/New Jersey swine-influenza vaccine in 1976) existed for the approximately 12.5 million adults (greater than or equal to 18 years old) vaccinated in the 1978-1979 influenza campaign. In the contiguous United States (excluding Maryland) 544 cases of GBS with onset between September 1, 1978, and March 31, 1979, were reported, including 12 adults who had been vaccinated within eight weeks before the onset of GBS and 393 who had not. The relative risk of vaccine-associated GBS for adults reported in this surveillance was 1.4 (95% confidence limits, 0.7 to 2.7)--significantly below the risk (6.2) associated with A/New Jersey vaccine for the equivalent eight-week period. In contrast to the A/New Jersey vaccine, the 1978-1979 influenza vaccine was not associated with a statistically significant excess risk of GBS.

Studies on the use of 9R strain of Salmonella gallinarum as a vaccine in chickens.

Abstract: The 9R strain of Salmonella gallinarum produced hepatitis and splenic lesions without mortality in meat-type and brown-egg-producing strains of chicks, but not in Leghorns. It was not recovered from Leghorns for as long following vaccination as from the other strains of chicks. The infectivity of the 9R strain was determined by the genetic susceptibility and age of the host. Subcutaneous vaccination of 9R produced partial immunity to S. gallinarum in Leghorns as well as in meat-type and brown-egg-producing strains of chickens. Addition of an oil adjuvant appeared to interfere with protection and gave even less protection than did a vaccine prepared from an inactivated oil-adjuvanted smooth strain. Use of the 9R vaccine did not protect against intestinal colonization by S. typhimurium or S. infantis. Potential egg transmission of 9R following vaccination and of a pathogenic strain following challenge of vaccinated birds was indicated by ovarian infection with each strain and by isolation of the pathogenic strain from one egg. All chickens vaccinated subcutaneously with the 9R strain developed antibodies detectable by the microantiglobulin test, but only a few birds developed antibody levels detected by the whole-blood, microagglutination, and tube tests. The inactivated vaccine prepared from a smooth S. gallinarum strain produced the highest and most uniform antibody response. Antibody levels were not related to protection, which is probably dependent on cellular immunity.

Streptococcus pneumoniae Polysaccharide Vaccine: Age and Dose Responses, Safety, Persistence of Antibody, Revaccination, and Simultaneous Administration of Pneumococcal and Influenza Vaccines

Abstract: Contemporary 14-valent pneumococcal polysaccharide vaccine was first licensed in 1977 in the United States, where about four million doses of vaccine have been distributed to date. The vaccine induces excellent antibody responses in elderly persons as well as in young adults. The antigen content of the vaccine is 50 microgram of each serotype of polysaccharide per dose, and lower titers of antibody are induced when the dose is reduced to 25 or 12.5 microgram of antigen. Adverse reactions are usually mild and consist principally of local erythema and induration at the injection site, with mild fever in a small proportion of subjects. Antibody persists well for at least four years, and it is expected that immunity will last for at least 5 years after vaccination. Local and systemic reactions to the vaccine may be greater when a second dose of vaccine is administered within three years after the initial dose, and this reactivity appears to be due to a Arthus-like response that results from local formation of antigen-antibody complexes. Pneumococcal and influenza vaccines can be injected simultaneously into separate sites without impairment of antibody responses to either vaccine; this feature should facilitate administration of these two vaccines.

The human cytotoxic T cell response to influenza A vaccination.

Abstract: The human cytotoxic T lymphocyte (CTL) response to challenge with influenza A vaccine was studied. Six of eight volunteers given killed whole influenza virus A/USSR (H1N1) vaccine showed substantial increases on the level of CTL memory 1 month after immunization. The CTL measured at this time showed complete cross-reactivity in their specificity for influenza A/USSR (H1N1) and A/X31 (H3N2) infected cells and also showed HLA restriction. The level of CTL memory increased in only three out of nine donors given subunit vaccine and showed no change in those not given vaccine. If cytotoxic T cells are important in influenza prophylaxis, killed whole virus vaccine should offer better protection than subunit vaccine.

Depression of Aminopyrine Metabolism by Influenza Vaccination

Abstract: HEPATIC cytochrome P-450 is important in the metabolism of many drugs.1 Multiple factors, such as ingestion of inducing agents (e.g., phenobarbital), nutritional state, and the presence of liver disease, influence hepatic levels of cytochrome P-450. Recent studies have demonstrated that immunologic stimulation by administration of bacillus Calmette–Guerin (BCG) vaccine,2 endotoxin,3 a group of interferon-inducing agents,4 and interferon itself,5 depresses hepatic cytochrome P-450 activity in laboratory animals. In human beings, viral upper-respiratory-tract infection appears to alter theophylline pharmacokinetics,6 , 7 and Renton et al. have reported that influenza vaccination impaired the elimination of theophylline in patients and healthy volunteers.8 We investigated the effect . . .

Guillain‐Barré syndrome: Its epidemiology and associations with influenza vaccination

Abstract: The epidemiology of Guillain-Barre syndrome (GBS) and the associations of GBS with influenza vaccination are described based on review of three types of epidemiological data: case-control studies, incidence rate studies of GBS in well-defined populations, and surveillance data from a sentinel neurologist surveillance system of GBS in the United States. These data indicate that the crude annual incidence rate of GBS per 100,000 people ranges from 0.6 to 1.9 in different populations in widely scattered areas of the world. In general, incidence rates are higher with advancing age until about 75 years, higher for men than women, and higher for whites than blacks. No specific HLA antigen has been significantly associated with GBS in general, although HLA AW 30 and AW 31 have been associated with chronic relapsing polyneuritis. Important trigger agents of GBS include nonspecific respiratory and gastrointestinal infections and cytomegalovirus infection. Influenza infection and influenza vaccinations are not generally important trigger agents. A major exception to this is the occurrence of just under 1 excess case of GBS per 100,000 A/New Jersey influenza vaccinations administered in the United States, 1976-1977. A significant excess risk of GBS was not observed after administration of influenza vaccine in 1978-1979 and 1979-1980. The differences between the contents of and immunological reaction to A/New Jersey influenza vaccine and the more recent influenza vaccines deserve further study.

Whooping cough in adults.

Abstract: During the 1970s whooping cough returned in Sweden after an absence of more than 10 years and is now seen in all age groups, During a three-year period 174 adults with culture-verified whooping cough were identified in Gothenburg. Most of the patients had typical symptoms with whooping attacks and often vomiting. The disease was long lasting but complications were rare. Physicians should be aware that whooping cough may occur in adults, since adults may be an important source of infection for infants and erythromycin given in the catarrhal phase may modify the clinical course.

Response to Pneumococcal Vaccine in Renal Transplant and Hemodialysis Patients

Abstract: Because of the risk of serious pneumococcal infections in patients receiving a renal transplant, a study was undertaken to determine if pneumococcal vaccine could be administered before or after transplantation. Vaccine was given to recipients of transplants and to patients who were undergoing dialysis. Both groups responded to the vaccine, and although the mean antibody levels were lower than those reported for normal populations, the levels were in the range thought to be protective for most pneumococcal types. Antibody levels, both before and after vaccination, were substantially lower in patients with recent transplants than in patients who were undergoing hemodialysis. Patients who are awaiting renal transplantation can be immunized while they are undergoing hemodialysis. Further study is needed to determine how long antibody levels will persist after vaccination in both patients undergoing hemodialysis and those receiving a transplant.

A Study of the Pneumococcal Vaccine in Prevention of Clinically Acute Attacks of Recurrent Otitis Media

Abstract: A total of 827 infants and children three months to six years of age were vaccinated randomly, after an attack of otitis media, with either the 14-valent pneumococcal vaccine or a control vaccine against Hemophilus influenzae type b. Clinically acute attacks of otitis media that occurred >14 days after vaccination were analyzed by culture of the middle ear fluid. Children who had received the pneumococcal vaccine at the age of seven to 83 months experienced within the first six months after vaccination significantly fewer attacks of otitis media caused by Streptococcus pneumoniae than did children in the control group (50% overall reduction, P < 0.01). The reduction of attacks was specific to those pneumococcal types/groups present in the vaccine that induced a good serum antibody response; the specific protection indicated for vaccine types/groups other than 6 (to which the antibody response was very poor) was 67% (P< 0.001). No or very little protection was seen in infants younger than seven months or in any children later than six months after vaccination. Several lines of preliminary evidence have suggested that active immunization might affect the course of acute otitis media caused by Streptococcus pneumoniae. Antibodies to the organism isolated from the middle ear fluid of patients with otitis media are found in the serum or middle ear fluid of such patients [1, 2]. The presence of antibodies is associated with faster resolution of the infection [3] and reduced frequency of recurrences caused by the same organism [4]. In an experimental model of pneumococcal otitis media in chinchillas, protection by parenteral vaccination was found to be promising [5, 6, 7]. Immunization

Use of Pneumococcal Vaccine for Prevention of Recurrent Acute Otitis Media in Infants in Boston

Abstract: The efficacy of pneumococcal polysaccharide vaccine for children suffering from recurrent acute otitis media (AOM) was determined by administration, in a randomized double-blind fashion, of one of two polyvalent vaccines to 124 children aged five to 21 months. The octavalent vaccine contained serotypes commonly associated with AOM: 1, 3, 6A, 7F, 14, 18C, 19F, and 23F. The heptavalent control contained serotypes not commonly associated with AOM: 2, 4, 5, 8, 9N, 12F, and 24F. Recipients of the octavalent vaccine experienced significantly (P less than 0.05) less AOM due to serotyes contained in the octavalent vaccine than did children who received the control vaccine. Although the recipients of octavalent vaccine suffered less from AOM due to types in that vaccine than did controls, their clinical experience with AOM was not different. Both groups of children were equally likely to experience at least one episode of AOM after vaccination (70% for octavalent vaccine and 78% for heptavalent vaccine). The mean numbers of episodes of AOM after vaccination also were similar (2.1 for octavalent vaccine and 2.3 for heptavalent vaccine). Similarly, the period of effusion in the middle ear after pneumococcal AOM was identical for both groups. Although immunization with pneumococcal vaccine appeared to reduce the number of episodes of AOM due to serotypes contained in octavalent vaccine, the clinical experience of the children was not favorably affected by this vaccine.

Development of a highly infective babesia bigemina vaccine of reduced virulence

Abstract: The virulence of a strain of Babesia bigemina was reduced by syringe passaging at 3 to 16-week intervals in a series of 7 calves. The calves were splenectomised 1 to 14 weeks after inoculation to induce the relapse parasitaemias used for passaging. Parasites taken at relapse from the last 3 calves in the series were inoculated into splenectomised calves from which highly parasitised blood for vaccine was obtained. The vaccine produced mild infections in 32 recipient cattle. When challenged either 5 weeks or 7 months after vaccination, the cattle had substantial immunity to a heterologous strain of B. bigemina.

Effect of vaccination on severity and dissemination of whooping cough.

Abstract: A study was undertaken in general practice to clarify those factors, especially vaccinations, that influence the clinical picture and infectivity of whooping cough in the community. Although the range of the disease encountered was fairly mild, its duration was notable (mean +/- SD 50.9 +/- 32.1 days). By using multiway contingency table analysis it was found that in the more severe cases of whooping cough vaccination significantly shortened the illness (p less than 0.005) and reduced the number of coughing spasms (p less than 0.025). The protective effect of the vaccine was most notable in modifying infectivity within the family: 19% of vaccinated family contacts of index patients in whom the disease had been confirmed bacteriologically developed the disease when exposed to it compared with 72% of non-vaccinated contacts (p less than 0.001). These results show that whooping cough vaccination modifies the clinical illness and offers a worthwhile degree of protection to children exposed to the disease.

Protection against feline leukemia by vaccination with a subunit vaccine.

Abstract: An effective vaccine against feline leukemia virus infection has been developed by the collection and concentration of tissue culture medium harvested from a tumor cell line Lymphoid cells were grown to near saturation density in a normal growth medium and then transferred to a serum-free medium The serum-free medium was collected, concentrated, and evaluated for its vaccine potential Cats receiving the vaccine emulsified in complete Freund adjuvant developed high antiviral and antitumor titers and were protected (81%) against virus challenge Cats receiving the vaccine without an adjuvant developed lower antibody levels and lower protection (53%) from viremia Age-matched and litter-matched controls developed no antibody to test antigens before the challenge, and 100% became persistently viremic after the challenge Vaccination with the soluble tumor cell antigen vaccine proved successful in preventing the induction of feline leukemia virus infection

Pneumococcal vaccine in the United States. A critical analysis.

Abstract: The capsular polysaccharide pneumococcal vaccine approved by the Food and Drug Administration in November 1977 has been recommended for persons older than 2 years believed to be at high risk for pneumococcal disease, including those aged 50 years and older, those with chronic systemic illnesses, and those living in certain institutions. A critical review of the available evidence shows little documentation of an increased incidence of, or mortality from, pneumococcal disease for many of these suggested categories. Moreover, except for children with sickle cell disease, there is no convincing evidence that the vaccine is effective for the chronically ill, and unpublished controlled studies have demonstrated no benefit for ambulatory, elderly, or institutionalized patients. Thus, there is currently no information to support widespread pneumococcal vaccination in this country, and further investigations are needed to determine in what situations this vaccine is worthwhile. ( JAMA 1981;246:1428-1432)

Efficacy of Pneumococcal Polysaccharide Vaccines

Abstract: due to pneumococcal infection. Estimates based on data obtained in this country after licensure of the vaccine suggest that the efficacy in certain groups may be low: <0% in children two to 10 years of age and 49% (95% confidence interval, <00%-75%) in persons older than 10 years of age. In the three years since relicensure of the pneumococcal vaccine, recommendations by individual physicians and by departments of public health for its use in this country have been somewhat tentative [1]. The data required before more definitive recommendations can be made include those on the efficacy of the vaccine in the target groups, i.e., the percentage reduction in rate of vaccinetype pneumococcal disease among a vaccinated population compared with the rate in an unvaccinated population, and the effectiveness of the vaccine, i.e., the effect of vaccination on overall morbidity and mortality. This latter quality depends on the incidence of the vaccine-preventable disease, on whether vaccine-type disease is replaced by disease due to other pneumococcal serotypes or organisms other than pneumococci, and on the duration of protection by the vaccines in addition to the vaccine's actual efficacy. This paper will review the current data on vaccine efficacy derived from prelicensure clinical trials and

Replication of infectious laryngotracheitis virus in chickens following vaccination.

Abstract: SUMMARY The site of replication of infectious laryngotracheitis vaccine virus (ILTV) was studied in chickens vaccinated by drinking water (DW), intraconjunctival (IC) and cloacal (CL) routes. The anatomical sites exposed to vaccine were determined by simulating vaccination with rhodamine red dye. Virus replication was determined by recovering virus from various organs at necropsy. The dye simulation studies clearly demonstrated that DW vaccination did not usually expose susceptible target organs to virus while the CL and IC routes flooded susceptible organs with vaccine. Virus replication was confined to the cloaca in CL vaccinated birds while in IC and DW vaccinated birds most replication took place in the nasal cavity. Vaccine virus did not always become established in DW vaccinated birds and its establishment did not appear to be related to the amount of vaccine these birds were exposed. It was concluded that DW vaccination depends for its success upon the accidental contamination of the nasal cavity with vaccine virus during the act of drinking.

The Pathogenesis of Pneumococcal Otitis Media in Chinchillas and the Efficacy of Vaccination in Prophylaxis

Abstract: Acute pneumococcal otitis media was produced experimentally in 100% of chinchillas whose middle ear cavities were inoculated with Streptococcus pneumoniae. Although intranasal inoculation with S. pneumoniae led to otitis media in 21% of animals, 66% of the colonized chinchillas that had negative pressure in the middle ear developed otitis media. Intranasal inoculation with S. pneumoniae followed by intranasal inoculation with influenza A virus led to otitis media in 73% of chinchillas, while inoculation with infleunza A virus alone produced otitis media in 4% of animals. Measurement of middle ear pressure by tympanometry showed the influenza virus-infected chinchillas developed negative middle ear pressure before the appearance of clinical signs of otitis media. While direct inoculation of the middle ear with pneumococci produced a purulent effusion within days after inoculation, intranasal inoculation with both pneumococci and influenza A virus resulted in the rapid appearance of a serous effusion, which became culture-positive for S. pneumoniae during the second week after inoculation. Spontaneous resolution of middle ear infection occurred within three to eight weeks after inoculation and was associated with an increase in the level of type-specific pneumococcal antibody in serum and middle ear effusion. The histopathology of pneumococcal otitis media included purulent middle ear effusion, epithelial metaplasia, and subepithelial edema and hypercellularity. The initial infiltration of the subepithelial space with polymorphonuclear leukocytes was superceded by infiltration with mononuclear leukocytes in animals that were observed for longer than eight weeks. Among untreated animals observed for long periods, production of granulation tissue, development of submucosal fibrosis, and osteoneogenesis were observed. Systemically administered pneumococcal capsular polysaccharide vaccine was effective for prevention of type-specific otitis media in chinchillas when vaccinated animals were challenged by intranasal inoculation with pneumococci followed by deflation of the middle ear. Animals that seroconverted with at least a twofold increase in the level of antibody in serum after vaccination had an 87% lower incidence of otitis media than did unvaccinated animals. Protection was associated with high levels of antibody in serum before intranasal inoculation, and higher antibody levels were found in sterile middle ear effusions than in effusions that contained pneumococci.

Dengue-2 vaccine: virological, immunological, and clinical responses of six yellow fever-immune recipients.

Abstract: Six male volunteers, previously immunized with yellow fever vaccine, were inoculated subcutaneously with a live, attenuated dengue-2 virus (PR-159/S-1) candidate vaccine. Five recipients developed viremia 8 or 9 days after vaccination, which lasted 1 to 10 days. The onset of viremia was followed by fever in three people, transient leukopenia in four, and an erythematous rash in one. One volunteer developed an oral temperature of 38.8 degrees C with headache, myalgia, fatigue, and photophobia suggestive of mild dengue fever. All five viremic volunteers developed fourfold or greater rises in serum neutralizing antibody. The sixth volunteer, who had a low titer of preexisting dengue-2 neutralizing antibody, had no viremia, no symptoms, and a modest rise in hemagglutination inhibiting antibody. Virus isolates obtained from plasma retained the small-plaque and temperature-sensitive growth characteristics of the vaccine virus in vitro. In this study, the vaccine virus genetically stable and immunogenic and seemed sufficiently attenuated for additional testing in humans.

Type-Specific vs. Cross-Protective Vaccination for Gram-Negative Bacterial Pneumonia

Abstract: Groups of guinea pigs received four injections intramuscularly of lipopolysaccharide vaccine derived from Pseudomonas aeruginosa, cross-protective core glycolipid vaccine derived from the J-5 mutant of Escherichia coli O111, or saline during a two-week period. Titers of passive hemagglutinating antibody to vaccine antigens in serum routinely increased fourfold or more. Experimental hemorrhagic pseudomonas pneumonia was then induced, from which the rates of survival were 15% among animals receiving saline, 81% among animals receiving pseudomonas vaccine (P less than 0.001), and 42% among animals receiving J-5 vaccine. Thus, only weak cross-protection against pseudomonas pneumonia was detected in the recipients of J-5 vaccine. Further studies revealed no protection against pneumonia due to either E. coli or Klebsiella in animals receiving J-5 vaccine. From these data, species-specific vaccination appears to be superior to vaccination with cross-protective antigen against experimental pseudomonas pneumonia.

Vaccination-Associated Relapse of Immune Thrombocytopenia

Abstract: Many patients with immune thrombocytopenia require splenectomy to achieve remission. They are therefore at risk for postsplenectomy septicemia and should receive vaccination against Streptococcus pneumoniae . In experiment situations, antigens contained within this vaccine can initiate a polyclonal B-lymphocyte activation and increased production of specific and nonspecific antibodies. In certain animal models, a polyclonal B-lymphocyte stimulatory response can trigger an autoimmune disorder. Two patients with immune thrombocytopenia had relapses of their immune thrombocytopenia after the administration of pneumococcal and influenza vaccines. These observations suggest that patients with a history of immune thrombocytopenia should be monitored after vaccination. ( JAMA 1981;245:369-371)

Vaccination of chickens with nonpathogenic Mycoplasma gallisepticum as a means for displacement of pathogenic strains.

Abstract: Attempts to solve the problem of Mycoplasma gallisepticum (Mg) infection of poultry by a combination of eradication and antibiotic treatment have at best met with only partial success. As a result of the continuing economic burden of the disease, there has been a renewed interest in vaccination as a tool in the control of Mg. A particularly pressing problem exists in the commercial egg industry, where the occurrence of MG infection of layer hens at the onset of egg production leads to a marked depression in productivity. Vaccination with the F strain of Mg has been demonstrated to efficacious in the alleviation of this problem, and the procedure is widely employed in the USA. Under field conditions of vaccination the F strain was found to be virtually nonpathogenic, although challenge experiments show that it retains some pathogenicity. The strain is carried in the trachea of vaccinated layers for as long as one year, but only spreads slowly. A specific serological response to Mg is produced in response to vaccination. To some extent, this response is dose dependent, but it is quantitatively less than that produced by virulent strains introduced by the same route. It has been suggested that the continued presence of a nonvirulent Mg in the upper respiratory tract, and the concomitant local immunological response, may prevent infection by field strains of Mg. In fact, judicious vaccination procedures appear to lead to the displacement of pathogenic Mg by the vaccine strain. By these means, it may be possible to eradicate Mg from flocks while maintaining production.