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Branching process models for surveillance of infectious diseases controlled by mass vaccination.

Mass vaccination programmes aim to maintain the effective reproduction number R of an infection below unity. We describe methods for monitoring the value of R using surveillance data. The models are based on branching processes in which R is identified with the offspring mean. We derive unconditional likelihoods for the offspring mean using data on outbreak size and outbreak duration. We also discuss Bayesian methods, implemented by Metropolis-Hastings sampling. We investigate by simulation the validity of the models with respect to depletion of susceptibles and under-ascertainment of cases. The methods are illustrated using surveillance data on measles in the USA.

Bayes Theorem↗

Ring vaccination versus mass vaccination in event of a smallpox attack.

Since vaccination is critical in responding to smallpox exposure, vaccination strategies must be evaluated during bioterrorism preparedness. Information on historical factors, smallpox characteristics, public health capabilities and hypothetical attack scenarios was used to evaluate major vaccination strategies. In event of a smallpox attack, the optimal strategy is situational, mass vaccination may be best for dense island populations such as Oahu.

Bioterrorism↗

The risk of aseptic meningitis associated with the Leningrad-Zagreb mumps vaccine strain following mass vaccination with measles-mumps-rubella vaccine, Rio Grande do Sul, Brazil, 1997.

BACKGROUND: Few data are available on the risk of aseptic meningitis following vaccination with the Leningrad-Zagreb (L-Z) strain of mumps vaccine. In 1997 the mumps vaccine was introduced into the state of Rio Grande do Sul in Brazil through mass vaccination with mumps-measles-rubella (MMR), targeting children aged 1-11 years. Five municipalities used exclusively MMR vaccine containing the L-Z strain of mumps. An outbreak of aseptic meningitis was observed shortly after the mass campaign. METHODS: To estimate the risk of aseptic meningitis associated with this strain, we analysed vaccination and meningitis case surveillance data from the selected municipalities. A case of vaccine-associated aseptic meningitis was defined as one with a pleocytosis of 10-1,500 leukocytes/ml and occurring within 15-35 days after vaccine receipt. RESULTS: We estimated a risk of 2.9 cases per 10,000 doses of L-Z administered, equivalent to 1 case per 3,390 doses administered. The overall risk of aseptic meningitis following the campaign was increased 12.2-fold (95% CI: 6.0-24.7) compared with the same period in 1995-1996. Following the mass campaign, the incidence of mumps declined 93% during 1998-2000. CONCLUSIONS: Vaccination with the L-Z strain of mumps vaccine as part of a mass campaign was associated with a significantly increased risk of aseptic meningitis. Decisions about type of mumps vaccine and mumps vaccination strategies must consider vaccine safety issues in addition to other criteria.

Brazil↗

Increased immunogenicity of oral poliovirus vaccine administered in mass vaccination campaigns compared with the routine vaccination program in Jordan.

To compare the immunogenicity of routine versus mass campaign doses of oral poliovirus vaccine (OPV), serum neutralizing antibodies were measured in 254 children before and after two mass vaccination campaigns in Jordan. Precampaign seroprevalences to poliovirus types 1, 2, and 3 in children who had received three, four, or five routine doses of OPV were compared with postcampaign seroprevalences in children who had received one, two, or three routine doses plus two mass campaign doses. Seroprevalences were consistently higher in subgroups that received two doses through mass campaigns than in subgroups that received all doses through the routine program, especially for poliovirus type 3. Geometric mean titers were also consistently higher for mass campaign subgroups, particularly for poliovirus type 3. The findings suggest that adding further doses of OPV to the routine schedule is unlikely to have as great an impact on the immune state of children as administering the same number of doses during mass campaigns.

Child, Preschool↗

A modified immunisation schedule for the hepatitis B vaccine Recombivax HB suitable for mass vaccination in childhood.

Following the demonstration of a fully satisfactory immunogenic activity of a hepatitis B vaccination protocol consisting of three doses of Hevac B Pasteur vaccine given at 3,5 and 11 months of age, it was possible to administer this vaccine at the same times as the vaccinations for diphtheria, tetanus and polio which are mandatory in Italy at those ages. We have also shown that both another plasma-derived vaccine, H-B-VAX (MSD), as well as the DNA-recombinant Engerix B (SK&F) are highly immunogenic when given at the same times as the mandatory childhood vaccinations. In this paper we demonstrate that the same schedule can be used for another hepatitis B vaccine prepared by a DNA-recombinant technique, Recombivax HB (MSD) recently introduced in Italy. In fact two doses of this vaccine, the first given at three months of age and the second two months later, resulted in a 100% seroconversion rate and a mean anti-HBs titre of 440 mUI/ml. Although the date are incomplete since the third dose will be given at 11 months of age, we conclude that this hepatitis B vaccine can also be used in the mass vaccination campaigns of infants in Italy, the first of which was initiated in January 1987 in an hyperendemic area near Naples (HBsAg prevalence about 14%). We underline that this mass vaccination campaign is the first in Europe.

Hepatitis B↗

Mass vaccination: when and why.

With increased demand for smallpox vaccination during the nineteenth century, vaccination days--early mass vaccination campaigns--were conducted over time-limited periods to rapidly and efficiently protect maximum numbers of susceptible persons. Two centuries later, the challenge to rapidly and efficiently protect populations by mass vaccintion continues, despite the strengthening of routine immunization services in many countries through the Expanded Programme on Immunization strategies and GAVI support. Perhaps the most widely accepted reason for mass vaccination is to rapidly increase population (herd) immunity in the setting of an existing or potential outbreak, thereby limiting the morbidity and mortality that might result, especially when there has been no routine vaccination, or because populations have been displaced and routine immunization services disrupted. A second important use of mass vaccination is to accelerate disease control to rapidly increase coverage with a new vaccine at the time of its introduction into routine immunization programmes, and to attain the herd immunity levels required to meet international targets for eradication and mortality reduction. In the twenty-first century, mass vaccination and routine immunization remain a necessary alliance for attaining both national and international goals in the control of vaccine preventable disease.

Communicable Disease Control↗

Mass vaccination for annual and pandemic influenza.

Influenza virus causes annual epidemics and occasional pandemics. Frequent mutations in circulating influenza strains ("antigenic drift") result in the need for annual vaccination. More than two-thirds of persons in the U.S. are recommended for annual vaccination. Because influenza vaccine is available seasonally, mass vaccination strategies are well suited to its delivery. Although doctors offices are the most frequent setting for influenza vaccination overall, workplaces, clinics, and community sites (retail stores and pharmacies) also are common vaccination settings. Influenza vaccination also is delivered in mass vaccination clinics to health care workers and military personnel. Universal influenza vaccination, which has been recommended as a strategy to improve prevention by increasing vaccination coverage and providing indirect protection of adults by decreasing infection and transmission among children, would require expanded use of mass vaccination, for example in schools, as well as in the community. Influenza pandemics occur when a new influenza A subtype is introduced into the population ("antigenic shift"). Most or all of the population is susceptible to the pandemic virus and two doses of vaccine may be needed for protection. U.S. pandemic preparedness and response plans indicate that the entire population should be vaccinated beginning with defined priority groups including those who provide essential services including healthcare and those at highest risk of severe illness and death. Pandemic influenza vaccination will occur primarily through the public sector in mass clinic settings. Vaccination program planning must consider issues including coordination, staffing, clinic location and lay-out, security, record keeping, and communications. Exercising vaccination clinics is important for preparedness and can be done in the context of annual influenza vaccination.

Communication↗

Control of epidemic meningococcal meningitis by mass vaccination. I. Further epidemiological evaluation of groups A and C vaccines in northern Nigeria.

Mass vaccination campaigns were mounted by several state governments in the northern Nigerian sector of the African meningitis belt. Bivalent groups A and C polysaccharide vaccines were used. The results of these campaigns in four of the states which are adjacent to each other are presented and assessed. A total of 7535350 persons in the four States, Bauchi, Borno, Gongola and Plateau, were given the vaccine over a period of 4 years (1978-1981). There was a decline in the overall number of cases reported as well as in the number of deaths in the area, where, since 1978, there has not been an epidemic of meningococcal meningitis. Variations were observed among the states which vaccinated over 50% of their populations and had many fewer cases than those which did not. These results show that mass vaccination is an effective means of preventing outbreaks of meningococcal meningitis and may lead to eradication of the disease.

Adolescent↗

The status of measles after five years of mass vaccination in the USSR.

Mass vaccination of children from 10 months to 8 years old with the original live vaccine prepared from the Leningrad-16 strain has led to a sharp decline in measles morbidity and mortality, and changed its epidemic pattern. In 1972, after 5 years of mass vaccination, the morbidity rate was 117.5 per 100 000 persons, whereas before vaccination the average annual morbidity rate was about 827.0. The periodicity of increases in morbidity every 3 years was also broken, the last peak of measles morbidity occurring in 1965. Another result of vaccination is that the formerly much higher morbidity rate in urban areas is now lower than that in rural areas. The mortality rate decreased more than 3-fold compared with the period before vaccination, and recently no deaths were registered in a number of regions. The serologic examination of 7 585 vaccinated children from 10 different regions revealed antibodies with a mean geometric titre of 78.6+/-1.16 in 90% of individuals. The high antibody level was maintained for 7 years after vaccination. The effect of vaccination is both epidemiological and economical. The saving in the use of gamma-globulin alone covered the cost of the vaccine and the expenses involved during vaccination.

Antibodies, Viral↗

Poliomyelitis in Japan during the period 1962-68 after the introduction of mass vaccination with Sabin vaccine.

After the mass vaccination of children of susceptible age groups in Japan in 1961, the incidence of poliomyelitis decreased markedly. From 1962 to 1968 a total of 659 paralytic cases were officially notified. Detailed investigations of 626 cases reported to the Poliomyelitis Surveillance Committee revealed that only 185 (29.6%) were cases of paralysis clinically typical of poliomyelitis. Tests on 120 of these 185 cases showed that 75 (62.5%) were positive for poliovirus: 45 of these positive cases were temporally associated with the administration of live poliovirus vaccine and 36 had some residual disability. Wild types of poliovirus were rarely isolated. Only 36 vaccine-related cases of poliomyelitis were observed among the total of more than 11 million newborn infants vaccinated with Sabin vaccine in the period 1962-68.

Adolescent↗

Adherence of mass vaccinators to timing guidelines for influenza vaccination.

BACKGROUND: With recent delays in influenza vaccine availability, practitioners have been encouraged to time vaccination activities to promote vaccination of high-priority groups first. This cross-sectional survey of persons vaccinated in nontraditional settings (NTS) by mass vaccinators was conducted to assess how effectively the mass vaccinators were able to implement these vaccination-timing guidelines. METHODS: In Minnesota, the Minnesota Visiting Nurse Agency (MVNA) is a major mass vaccinator in NTS. For the 2001-2002 vaccination season, MVNA developed several strategies designed to facilitate adherence to vaccination timing guidelines adopted by the Minnesota Department of Health. All persons vaccinated in the MVNA NTS clinics from October 2001 through December 2001 were surveyed in order to evaluate whether they were in a high-priority group and whether the timing of their vaccinations coincided with the timing promoted in the guidelines. RESULTS: A total of 46,174 of the 145,947 people vaccinated by the MVNA were vaccinated between October 14 and October 28, 2001, the time period designated for vaccination of high-priority groups. Of these, 41,143 (89%) responded to the priority group question and 27,211 (66%) indicated that they were in one of the targeted groups, including more than 19,000 Medicare recipients. At sites targeting senior citizens, more than 92% of initial vaccine recipients were in a targeted group. Overall, 48.4% of persons vaccinated at any time during the vaccination season were in a high-priority group. CONCLUSIONS: Mass vaccinators can successfully implement influenza vaccination timing guidelines in NTS.

Cross-Sectional Studies↗

Prevalence of antibodies against rubella virus in The Netherlands 9 years after changing from selective to mass vaccination.

A two-dose mass vaccination programme with a combined vaccine against measles, mumps and rubella (MMR) was adopted in the Netherlands in 1987, replacing the selective schoolgirl vaccination strategy introduced in 1974. To obtain insight into the effect of mass vaccination and the population's immunity, the antibody levels against rubella were studied in the general Dutch population and in religious groups refusing vaccination. In the national sample, we observed a high prevalence (96.5%) for rubella antibodies in vaccinated cohorts as well as in the older unvaccinated cohorts. No indications of rapidly waning immunity after vaccination were found. There are indications of low virus circulation in the last few years. The very high seroprevalence in women at childbearing age is consistent with the few reported cases of congenital rubella syndrome (CRS) at present. However, individuals in the age group of 1-9 years who are not vaccinated for religious or other reasons have a considerably lower seroprevalence and thus there is a potential risk of a CRS outbreak in the future.

Adolescent↗

Safety of the yellow fever vaccine during the September 2001 mass vaccination campaign in Abidjan, Ivory Coast.

In 2001, a vaccination campaign against yellow fever was carried out in Abidjan, Cote d'Ivoire. During the campaign and 4 weeks after an active surveillance system for adverse events following immunization (AEFI) was set up. More then 2.6 million doses were administered and 87 AEFI were notified. Eight suspected YF cases were reported after vaccination and considered as AEFI. However, none had IgM for YF and all recovered without sequels. This surveillance system provided reassuring data about the safety of the YF vaccine and proved that it is feasible to set up an active surveillance system during a mass campaign.

Adolescent↗

Persistent efficacy of live attenuated hepatitis A vaccine (H2-strain) after a mass vaccination program.

BACKGROUND: Live attenuated hepatitis A vaccine (H2 strain) is widely applied in prevention of hepatitis A epidemic in China and other countries now. It is essential to observe and confirm the vaccine immune efficacy, population antibody level and its persistent efficacy after mass immunization. METHODS: A total of 220 children with negative anti-HAV antibody (aged 1 - 3 years) were taken for follow-up assay to observe seroconversion and geometric mean titre (GMT) level 2 months, 12 months, 6 years, and 10 years after inoculation. Another survey sampled from subjects of different age groups (3, 6, 9, 15, 18, 25 and 35 years) to compare anti-HA antibody positive rate before and after inoculation performed 10 years previously. Epidemiological observations were taken for 10 years to evaluate the relationship between vaccine coverage and hepatitis A morbidity. Serum antibody to HAV was detected by enzyme linked immunoassay (ELISA, calibrated by WHO international reference) and ABBOTT Axsym HAVAB microparticle enzyme immunoassay. RESULTS: Seroconversion in follow-up assay 2 months and 10 years after inoculation was 98.6% and 80.2% respectively. For children, the vaccination anti-HA antibody positive rates were significantly different before and after 10 years, 7.69% cf 70.45% (aged 3 years) and 52.58% cf 71.78% (aged 18 years). When vaccine coverage rose from 57% to 74%, there were no any HA epidemics. When vaccine coverage reached 85%, there were no any HA cases. With vaccine coverage between 85% and 91%, there were no any HA cases in cohorts from the age of 1 year to 15 years during the 10 years. CONCLUSIONS: Live attenuated hepatitis A vaccine has an obvious long-term effectiveness in prevention and control of HA epidemics through mass vaccination.

Adolescent↗

Pertussis in England and Wales: an investigation of transmission dynamics and control by mass vaccination.

The epidemiology of pertussis and its prospects for control by mass vaccination in England and Wales are investigated by analyses of longitudinal records on incidence and vaccine uptake, and horizontal data on age-stratified case reports. Mathematical models of the transmission dynamics of the infection that incorporate loss of natural and vaccine-induced immunity plus variable vaccine efficacy are developed, and their predictions compared with observed trends. Analyses of case reports reveal that the individual force of infection is age dependent, with peak transmission in the 5- to 10-year-old age class. A model incorporating this age dependency, along with partial vaccine efficacy and loss of vaccine-induced immunity, generates predicted patterns that best mirror observed trends since mass vaccination was inaugurated in 1957 in England and Wales. Model projections accurately mirror the failure of mass vaccination to increase the inter-epidemic period of the infection (three years) over that pertaining before control. The analysis suggests that this is due to the impact of partial vaccine efficacy. Projected trends do not accurately reflect the low levels of pertussis incidence reported between epidemics in the periods of high vaccine uptake. This is thought to arise from a combination of factors, including loss of natural and vaccine induced immunity, biases in case reporting (where reporting efficiency is positively associated with the incidence of pertussis), and seasonal variations in transmission. Model predictions suggest that the vaccination of 88% of each birth cohort before the age of 1 year will eliminate bacterial transmission, provided the vaccine confers lifelong protection against infection. If vaccine-induced immunity is significantly less than lifelong (or if vaccination fails to protect all its recipients) repeated cohort immunization is predicted to be necessary to eliminate transmission. Future research needs are discussed, and emphasis is placed on the need for more refined data on vaccine efficacy, the duration of natural and vaccine-induced immunity and the incidence of clinical pertussis and subclinical infections (perhaps by the development of reliable serological tests). Future mathematical models will need especially to incorporate seasonality in transmission.

England↗