Mathematical modeling of delayed pertussis vaccination in infants.

Pertussis is an acute vaccine-preventable respiratory disease that remains a public health problem. In an attempt to improve the control of the disease, many countries have incorporated new boosters in their vaccination schedule. Since the incorporation of these boosters is relatively recent, there are not enough data about their impact to support and/or universalize their use. Alternative strategies such as the improvement in vaccine coverage and reduction in vaccination delays, in addition to the incorporation of boosters, could be implemented. Though these strategies are not new, they have not been adequately evaluated in order to be implemented and/or prioritized. To evaluate the potential impact of these alternative strategies on pertussis incidence, we developed a methodology that involves the use of data collected from vaccination centers and an age-structured deterministic mathematical model for pertussis transmission. The results obtained show that strategies that avoid delays in vaccination have a strong impact on incidence reduction in the most vulnerable population (infants less than 1 y). In regions with high vaccination coverage (95%) the elimination of delays in the three primary doses decreases pertussis incidence in infants by approximately 20%. In regions where delays in the administration of vaccines are higher, the combined action to reduce delays and improve coverage leads to a significant improvement in disease control in infants. By repeating the calculations using different sets of parameters that describe different possible epidemiologic scenarios, we determined the robustness of our results. All the results presented highlight the importance of having high vaccine coverage and shorter delays in vaccine administration in order to reduce the impact of the disease in infants.

Modelling the effect of changes in vaccine effectiveness and transmission contact rates on pertussis epidemiology.

The incidence of the highly infectious respiratory disease named pertussis or whooping cough has been increasing for the past two decades in different countries, as in much of the highly vaccinated world. A decrease in vaccine effectiveness over time, especially when acellular vaccines were used for primary doses and boosters, and pathogen adaptation to the immunity conferred by vaccines have been proposed as possible causes of the resurgence. The contributions of these factors are not expected to be the same in different communities, and this could lead to different epidemiological trends. In fact, differences in the magnitude and dynamics of pertussis outbreaks as well as in the distribution of notified cases by age have been reported in various regions. Using an age-structured mathematical model designed by us, we evaluated how the changes in some of the parameters that could be related to the above proposed causes of disease resurgence - vaccine effectiveness and effective transmission rates - may impact on pertussis transmission. When a linear decrease in vaccine effectiveness (VE) was assayed, a sustained increase in pertussis incidence was detected mainly in infants and children. On the other hand, when changes in effective transmission rates (ßij) were made, a dynamic effect evidenced by the presence of large peaks followed by deep valleys was detected. In this case, greater incidence in adolescents than in children was observed. These different trends in the disease dynamics due to modifications in VE or ßij were verified in 18 possible scenarios that represent different epidemiological situations. Interestingly we found that both incidence trends produced by the model and their age distribution resemble the profiles obtained from data reported in several regions. The implications of these correlations are discussed.

[Experience of the surgical service and surgeons at the 1st Surgical Clinical Center in Belgrade in the primary care of abdominal war injuries 1991-1992]. / Iskustvo hirurskih ekipa i hirurga I Hirurske klinike Klinickog centra u Beogradu u primarnom zbrinjavanju ratnih povreda abdomena 1991-1992]

During the recent (1991/92) war on the territory of the former Yugoslavia, 12 of our surgeons participated in the treating of war abdominal injuries, on 8 localities with the various characteristics of combat. Treating all injuries, with adequate evidence and documentation, the general experience of all participants of our team was that abdominal injuries range from 0-12% depending on the the intensity of combat, with the mean percentage of 5.43% while combined injuries approximate 50% with the most common injuries of extremities (24%). The number of laparotomies was 65. The most common cause of abdominal injuries were bullets (75%) except in the localities with heavy combat where the explosive and bullet woundings were equally observed. The blast injuries were recorded in 3%. The most common injured organs were large (29.5%), small intestine (23.46%) liver, stomach and spleen subsequently. The severity of injury and mortality depends mostly of the number of injured organs, and multiorgan lesions were systematically observed (1.89 of injured organs SD 0.96). The total hospital mortality was 6.15% (4 cases: 2 "in tabula" and 2 later) due to multiorgan injuries with severe shock and bleeding. To achieve better results, early transportation to a place where operation could be made is necessary, with the effective first aid and good organisation of the initial management and triage. The diagnosis must be fast and effective, decision quick and the operation must deal with all the injuries primary, by the most safe surgical procedure, with the exposition of external wound.