Determination of duration of immunity of calves vaccinated
with the Theileria annulata schizont cell culture vaccine.
Beniwal RK, Sharma RD, Nichani AK.
Department of Veterinary Medicine, CCS Haryana Agricultural University,
Haryana, India.
Bovine tropical theileriosis caused by Theileria annulata is a serious
haemoprotozoan disease of cattle affecting exotic cattle, their crossbreeds
and young indigenous calves. Cell culture vaccines have been developed and
used effectively in various countries for the control of this disease.
However, the duration of immunity provided by these vaccines is poorly
understood. The present experiments were planned to study the duration of
immunity in animals after vaccination with the T. annulata (Hisar) schizont
cell culture vaccine. Two groups of calves were vaccinated and challenged
after a period of 3 and 6 months, respectively. There was no fever in any of
the vaccinated calves after challenge. However, the vaccinated animals
exhibited mild to moderate enlargement of lymph nodes and parasitological
reactions. The parasitological reactions were very mild in calves challenged
after 3 months and moderate in calves challenged after 6 months. There was a
mild but significant decrease in the haematological values of calves after
challenge. A significant rise in the anti-theilerial antibody titres was
observed in all calves after vaccination, which increased further, by many
folds after challenge. On the other hand, all the challenge control calves
showed symptoms of acute theileriosis and died. The observations suggested
that the T. annulata (Hisar) schizont cell culture vaccine provided immunity
in vaccinated animals for at least 6 months in the absence of field tick
challenge. However, there was some
decline in immunity after 6 months, if the animals are not exposed to ticks
during this period.
Secondary measles vaccine failures identified by
measurement of IgG avidity: high occurrence among teenagers vaccinated at a
young age.
Paunio M, Hedman K, Davidkin I, Valle M, Heinonen OP, Leinikki P, Salmi A,
Peltola H.
Department of Public Health, University of Helsinki, Finland.
Failure to seroconvert (primary vaccine failure) is believed to be the
principal reason (approx. > 95%) why some vaccinees remain susceptible to
measles and is often attributed to the persistence of maternal antibodies in
children vaccinated at a young age. Avidity testing is able to separate
primary from secondary vaccine failures (waning and/or incomplete immunity),
but has not been utilized in measles epidemiology. Low-avidity (LA) and
high-avidity (HA) virus-specific IgG antibodies indicate primary and secondary
failure, respectively. Measles vaccine failures (n = 142; mean age 10.1 years,
range 2-22 years) from an outbreak in 1988-9 in Finland were tested for
measles-virus IgG avidity using a protein denaturating EIA. Severity of
measles was recorded in 89 failures and 169 non-vaccinees (mean age 16.2
years, range 2-22 years). The patients with HA antibodies (n = 28) tended to
have clinically mild measles and rapid IgG response. Among failures vaccinated
at < 12, 12-15 and > 15 months of age with single doses of Schwarz-strain
vaccine in the 1970s, 50 (95% CI 1-99), 36 (CI 16-56) and 25% (CI 8-42) had HA
antibodies, respectively. When a single measles, mumps and rubella (MMR)
vaccine had been given after 1982 at 15 months of age, only 7% (CI 0-14)
showed HA antibodies. Omitting re-vaccinees and those vaccinated at < 15
months, Schwarz-strain recipients had 3.6 (CI 1.1-11.5) higher occurrence of
HA responses compared to MMR recipients. Apart from one municipality, where
even re-vaccinees had high risk of primary infection, 89% (CI 69 to
approximately 100) of the infected re-vaccinees had an HA response.
Secondary measles-vaccine failures are
more common than was more previously thought, particularly among individuals
vaccinated in early life, long ago, and among re-vaccinees.
Waning immunity even among individuals vaccinated after 15 months of age,
without the boosting effect of natural infections should be considered a
relevant possibility in future planning of vaccination against measles.
MRC Laboratories, Fajara, Banjul, The Gambia. whittle@commit.gm
BACKGROUND: Despite a high coverage with measles vaccines in parts of west
Africa, epidemics of measles occur with reduced severity in an increasing
proportion of older children who have been vaccinated. We examined the effect
of exposure to natural measles on immunity in vaccinated children. METHODS:
Our study was carried out in 1992 during an epidemic of measles in Niakhar, a
rural area of Senegal with about 27,000 inhabitants who mostly live in
compounds that include several households; within each household people live
in different huts. Vaccine coverage in Niakhar was 81% at the time of our
study. We measured haemagglutinin-inhibiting antibody at exposure and twice
thereafter (after 4-5 weeks and at 6 months) in 36 vaccinated and 87
unvaccinated children. The frequency of measles and subclinical
measles--defined as a four-fold or greater rise in antibody titre without
clinical signs or symptoms--was related to intensity of exposure according to
whether the index case was in the same hut, household, or compound. FINDINGS:
Clinical measles occurred in 20 (56%) of 36 unvaccinated children and in one
(1%) of 87 vaccinated children. Subclinical measles occurred in 39 (45%) of 86
vaccinated children who were exposed to measles and in four (25%) of 16
unvaccinated children. The frequency was inversely related to pre-exposure
antibody concentration (p<0.001 for trend) and directly related to intensity
of exposure (p=0.002 for trend). Antibody concentrations in subclinical cases
increased on average by 45-fold and remained raised for at least 6 months.
INTERPRETATION: Increased antibody titre
after subclinical measles may be common in vaccinated children in West Africa
where the intensity of exposure is high. As measles vaccination coverage
increases, the circulation of wild measles will decrease, and vaccine-induced
antibody is less likely to be boosted.
Thus, new epidemics, albeit
milder in form, may occur in vaccinated areas which should be recognised in
campaigns to eradicate measles.
Department of Biological Sciences, University of Warwick, Conventry, England.
An increasing body of evidence
suggests that a substantial proportion of individuals who respond to measles
vaccine display an antibody boost accompanied by mild or no symptoms on
exposure to wild virus. It is unknown whether this emerging class of
individuals can support transmission. The epidemiologic consequences of
vaccinated individuals able to transmit virus are investigated using a
mathematical model. Parameters for this model are estimated using regression
analysis on a Canadian serologic data set. The authors confirm that
neutralizing antibodies are decaying significantly in absence of circulating
virus. Based on a protective threshold plaque reduction neutralization (PRN)
titer of 120, the authors estimate the mean duration of vaccine-induced
protection in absence of reexposure to be 25 years (95% confidence interval
(CI) 18, 48). After long-term absence
of circulating virus, the mathematical model predicts that 80% (95% CI 65, 91)
of all seroconverted vaccinees
have titers below the protective threshold. In this case, elimination
of measles virus cannot be achieved by a single-dose routine vaccination
strategy if the basic reproduction number in vaccinated individuals exceeds
1.24 (95% CI 1.10, 1.53). For this
reason, there is a need to establish the intensity and duration of
infectiousness in vaccinated individuals.
PMID: 10588085 [PubMed - indexed for MEDLINE]
AN: 20053306
A report of diphtheria surveillance from a rural medical college
hospital. Ray,-S-K;
Das-Gupta,-S;
Saha,-I J-Indian-Med-Assoc.
1998 Aug; 96(8): 236-8.
Journal-of-the-Indian-Medical-Association;
0019-5847
English
A 5-year sentinel surveillance of diphtheria from 1989 to 1993 was
undertaken at a rural medical college hospital.
No significant change in the number of
diphtheria
cases was observed in spite of sustained high level of diphtheria,
pertussis,
tetanus vaccine-3
doses (DPT3) coverage. Most of the diphtheria cases occurred
during July to November. Age distribution of diphtheria cases showed that
more than 75% occurred above 2 years age (except in 1989) and around 65% cases
above 3 years age. The age shift in diphtheria signified success of
primary diphtheriaimmunisation, as well as indicated the lack of
coverage with booster doses at appropriate ages.
Because of high coverage with primary
diphtheriaimmunisation
there was decrease in circulating toxigenic
C diphtheriae
resulting in less natural
boosting of antibody titre.
Thus, in absence of booster immunisation, the older children and adults
were more vulnerable to diphtheria. The findings of the study justified
the need of emphasising importance of booster diphtheriaimmunisation
at appropriate ages for effective control of diphtheria.
National-Library-of-Medicine
AN: 99047981
A study of maternally derived measles antibody in infants
born to naturally infected and vaccinated women.
Brugha R, Ramsay M, Forsey T, Brown D.
Immunisation Division, Public Health Laboratory Service (PHLS) Communicable
Disease Surveillance Centre, London.
Maternal, cord and infant measles antibody levels were measured and compared
in a group of 411 vaccinated mothers and 240 unvaccinated mothers, and their
babies, between 1983 and 1991. Maternal and cord sera were tested by
haemagglutination inhibition and/or enzyme-linked immunosorbent assay, and
plaque reduction neutralization tests were also used to test infant sera.
Geometric mean titres were significantly higher in the unvaccinated than in
the vaccinated mothers (P < 0.001). Infants born to mothers with a history of
measles had higher antibody levels at birth than infants of vaccinated mothers
and, although the difference narrowed over time, continued to have higher
levels up to 30 weeks of age. Between 5 and 7 months of age significantly more
of the children of vaccinated mothers had plaque reduction neutralization
antibody levels below that which would interfere with vaccination.
As the boosting effect of circulating
natural measles disappears, earlier measles vaccination may need to be
considered, perhaps as part of a two-dose policy.
Center for Disease Control and Prevention, Atlanta, GA, USA.
BACKGROUND: It is unknown whether
vaccine-induced immunity is lifelong in the absence of periodic exposure to
measles virus. After 27 years of no known exposure to measles, an
outbreak in Palau in 1993 offered the opportunity to study this issue and the
measles vaccine effectiveness. METHODS: Household contacts of a sample of
confirmed cases were interviewed for exposure, symptoms and vaccination status
verified by records. Serum from symptomatic contacts was tested for measles
antibodies. RESULTS: Among 78 contacts 4 of 5 (80%) unvaccinated, 4 of 35
(11%) 1-dose vaccine recipients and none of 38 (0%) > 1-dose recipients
developed measles. Effectiveness of 1-dose vaccine was 86% (95% confidence
interval, 60 to 95%). An additional dose significantly reduced the risk of
measles (P = 0.048). Time since vaccination was not a significant risk factor
for developing measles (relative risk, 1.6; 95% confidence interval, 0.3 to
9.4; persons vaccinated > 15 years ago vs. < 5 years ago). CONCLUSIONS:
Similar to the estimates previously obtained in the area, measles vaccine
effectiveness in Palau was lower than the estimates obtained in the US. A
second dose of vaccine further reduced the risk for developing measles.
We found no evidence that waning
immunity was an important problem in this limited population with no known
previous exposure to measles virus. The small number of vaccinated contacts
precludes a definitive assessment.
Diphtheria: changing patterns in the developing world and
the industrialized world.
Galazka AM, Robertson SE.
Global Programme for Vaccines and Immunization, World Health Organization,
Geneva, Switzerland.
In the past, diphtheria was considered one of the most serious childhood
diseases because it took a heavy toll in health and life among preschool-aged
children. Prior to the widespread availability of diphtheria toxoid, nearly
70% of cases were in children younger than 15 years of age.
In the industrialized countries,
immunization against diphtheria became widespread in the 1940s and 1950s. This
led to a marked decrease in the incidence of diphtheria. There was also a
decrease in circulating
toxigenic Corynebacterium diphtheriae
organisms, resulting in less natural boosting of antibody levels. This had led
to gaps in the immunity of the adult population. Since 1990, diphtheria
has made a spectacular comeback in several European countries, with a high
proportion of cases in adults. In developing countries, immunization of
infants with diphtheria toxoid was introduced with the Expanded Programme on
Immunization in the late 1970s. Coverage rose slowly to 46% in 1985 and 79% in
1992. Because the pool of immunized
persons is not yet large, the process of maintaining immunity still operates
through natural mechanisms, including frequent skin infections caused
by C. diphtheriae. But recently, several developing countries where coverage
has been high for 5-10 years have reported diphtheria outbreaks. These
outbreaks have been characterized by high case fatality rates, a large
proportion of patients with complications, and their occurrence in both young
and older age groups. In all countries, priority should be given to efforts to
reach at least 90% coverage with three doses of diphtheria toxoid in children
below one year of age. In countries where diphtheria has been successfully
controlled, immunity levels should be maintained by booster doses.
Medical Research Council Laboratories, The Gambia, West Africa.
The rate of decline in anti-PRP antibody levels was measured in two groups of
Gambian children who had been given PRP-OMPC at 1 and 3 months or 2 and 4
months of age. In the younger group (n = 70), the geometric mean titre fell
from 1.32 micrograms/ml at 4 months to 0.44 micrograms/ml at 18 months. In the
older group (n = 54), the geometric mean titre fell from 1.18 micrograms/ml at
5 months to 0.46 micrograms/ml at 18 months. The proportion of vaccinated
children with antibody levels over 1.0 microgram/ml fell from 54% 1 month
after the second dose of vaccine to 27% at the age of 18 months, while the
proportion with levels over 0.15 micrograms/ml fell from 82% to 60%, with no
significant differences observed between the vaccination groups.
For those children who did not show
evidence of environmental boosting, the half-life of anti-PRP
antibody was about 100 days. This did not differ between the groups.
These findings suggest that to provide lasting immunity PRP-OMPC should be
given with a late booster dose at 12-15 months, as is the current practice in
the USA. The need for a late booster dose may limit the value of this vaccine
in developing countries where vaccination of children is difficult after the
1st year of life.
Experience of vaccination with inactivated poliomyelitis
vaccines in Iceland.
Gudnadottir M.
Iceland, as a few other European countries, has used inactivated vaccine
against poliomyelitis from the beginning in 1956. No cases of paralytic polio
occurred since 1960. For 17 years neither isolations of poliovirus nor
suspected cases of the clinical disease have been recorded. Studies on
neutralizing antibodies in sera of vaccinees were not too encouraging after 4
injections. A 5th vaccination of IPV was therefore given to those children who
lacked antibodies to any type of poliovirus. One month after the 5th injection
70% had antibodies against all 3 types of poliovirus and only 2% lacked
antibodies against both types 1 and 3.
In countries where no virus to boost immunity exists any longer during the
life of an individual it may be necessary to secure booster effects at regular
intervals after primary vaccination and later in life. This will be
included in the vaccination schedule against polio in Iceland.
ALL INFORMATION, DATA, AND
MATERIAL CONTAINED, PRESENTED, OR PROVIDED HERE IS FOR GENERAL INFORMATION
PURPOSES ONLY AND IS NOT TO BE CONSTRUED AS REFLECTING THE KNOWLEDGE OR OPINIONS
OF THE PUBLISHER, AND IS NOT TO BE CONSTRUED OR INTENDED AS PROVIDING MEDICAL OR
LEGAL ADVICE. THE DECISION WHETHER OR NOT TO VACCINATE IS AN IMPORTANT AND
COMPLEX ISSUE AND SHOULD BE MADE BY YOU, AND YOU ALONE, IN CONSULTATION WITH
YOUR HEALTH CARE PROVIDER.
