Date Published: June 14, 2019
Publisher: Public Library of Science
Author(s): Zaurbek Sagiyev, Almas Berdibekov, Tatyana Bolger, Almagul Merekenova, Svetlana Ashirova, Zamir Nurgozhin, Zhandos Dalibayev, Chandra Shekhar Bakshi.
In Kazakhstan, a live plague vaccine EV 76 NIIEG has been used for plague prophylaxis since the mid-1930s. Vaccination is administered yearly among people living in plague-enzootic areas. Similar practices are used in other former Soviet Union countries. Yet, to this day, the effectiveness period of the vaccine is unknown. It is also not clear how different factors can affect the effectiveness of the vaccine over time.
We surveyed changes in antibody levels specific for F1 antigens of Yersinia pestis among vaccinated people 4, 8, and 12 months post- vaccination. Blood samples were taken from the participants of the study for producing sera, which was later analyzed using indirect hemagglutination reaction with antigenic erythrocyte assay (micromethod) for identifying antibodies to F1 Y.pestis.
In first-time-receivers of the plague vaccine, antibody titer reached the highest level of antibody that represents a conditionally protective titer after 4 months, dropped drastically after 8 months, and dropped again after 12 months. Similar results were obtained among those who have been vaccinated previously. However, in that group, the percentage of people with a level of antibody that represents a conditionally protective titer remained statistically significant even after 8 and 12 months.
Based on the results of this study, we recommend initiating vaccination campaigns for the medical and veterinary staff, as well as the general population four months prior to the springtime epizootics of plague among wild rodents.
Since plague has taken many human lives in the past. It is not surprising that one of the first attempts to create a vaccine was an attempt to develop a vaccine against the plague. The first effective plague vaccine was created by The Institut Pasteur in late 1890s. It was a killed vaccine. After that, live attenuated vaccines were developed . Currently, two types of plague vaccines are used globally: killed-whole cell (KWC) and live whole-cell (LWC). KWC vaccines use virulent strains killed by heating or adding formaldehyde, whereas LWC vaccines are created on the basis of virulent Y. pestis strains [2, 3, 4, 5,6].
493 people vaccinated with LWC vaccine EV 76 NIIEG, ages 20 to 69, participated in the study, including 243 men and 250 women. 352 were vaccinated against plague 1–4 times, while 141 people have received vaccine 5 or more times. The vaccinated people worked in different institutions (Table 1).
In Kazakhstan, the plague enzootic area is 1,007,350 km2 wide (Fig 1). KSCQZD (M. Aikimbayev’s Kazakh Scientific Center for Quarantine and Zoonotic Diseases) and anti-plague stations carry out the plague surveillance of this territory . The LWC vaccine EV 76 NIIEG is used for plague prophylaxis. Vaccination is administered yearly in springtime among people living in plague-enzootic areas. Public health organizations give recommendations on whom to vaccinate against plague. When plague epizootics are identified, the population of the epizootic areas, as well as veterinarians, farmers, the staff of anti-plague organizations working in the area and tourists visiting the area are vaccinated. The study was conducted between April 15, 2014 and April 15, 2015.
At this time, there are no alternatives to the existing plague vaccines. Attempts at creating new vaccines are being made around the globe. One such example is the development of a subunit vaccine [6, 9, 15]. In the meantime, the existing plague vaccines will keep being used to protect the population of enzootic areas, the staff of laboratories working with Y.pestis, and to protect the civilians in case of a biological or terrorist attack using Y.pestis . The live plague vaccine EV NIIEG saved thousands of lives in the 20th century and is still being used for annual routine vaccination of laboratory staff and the population of enzootic areas in former Soviet states [2,16].
Due to financial constraints, we used indirect hemagglutination reaction for detecting antibodies against capsular antigen Y.pestis. In the future, we plan to conduct a similar study using immunoassay analysis. Indirect hemagglutination reaction allowed us to detect antibodies only against F1 Y. pestis, while immunoassay analysis could help detect other Y. pestis antigens, Pla, LcrV, YopM, and YscF.