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Information expert Janez Žibert: 70% vaccination would nullify the effect of the delta version in Slovenia

By: Domen Mezeg / Nova24tv

“Based on the presented analysis, we can therefore conclude that vaccination has a key impact on the course of the covid-19 epidemic in Slovenia and is absolutely necessary to prevent overloading the health system,” dr. Janez Žibert from the Faculty of Computer and Information Science in Ljubljana established based on the analysis.

Janez Žibert, a professor at the Faculty of Computer and Information Science, prepared an analysis of the “impact of vaccination on the course of the epidemic in Slovenia”. The analysis compares the possible course of the epidemic in Slovenia with respect to different assumed vaccination courses with the actual situation of the epidemic and vaccination in Slovenia in 2021. The purpose of the study is to determine how effective vaccination is in combating the covid-19 epidemic on specific epidemic data in Slovenia, states Žibert. The analysis covers the period from January 1st, 2021 to November 1st, 2021.

During this time, the majority of vaccinations in Slovenia were also carried out. Two periods are included in the analysis for comparison: the first is from January 1st, 2021 (MO cut-off date) to June 1st 2021 (M1 cut-off date), and the second period is from June 1st, 2021 to November 1st, 2021 (M2 cut-off date). In the first period, the vaccination was more intense, and at the same time, in the second, a delta, a more contagious version of the coronavirus, also appeared. Four vaccination scenarios are considered in the analysis. At the same time, a comparison is made between these scenarios, taking into account the confirmed number of infections in the periods under consideration, the number of hospitalisations, treatments in intensive care units and the number of deaths.

Additional explanation for graph S4: “For example, this means that if the vaccination rate in a certain age group was, say, 20% on May 1st, 2021, the increase factor 1.3 increases this share to 1.3 ⋅ 20% = 26%, and the reduction factor 0.7 reduces this share to 0.7 ⋅ 20% = 14% on that date and so on for each day and each age group.” Actual vaccination rates (S1 scenario), at cut-off dates in columns 2 and 3: the total vaccination rate until June 1st, 2021 was 20.92 percent and the total vaccination rate until November 1st, 2021 was 52.89 percent. The second vaccination scenario does not envisage at all, so all proportions are equal to 0%. According to scenario S3, the vaccination rate for June 14th, 2021 is 14.65% and for November 1st, 2021 37.02%.

According to the S4 scenario, the vaccination rate for the first cut-off date is 26.20 percent, and for the second 68.90 percent, which is almost 70 percent. At the same time, extremely high vaccination rates are assumed in the age group over 65 years and around 85% of vaccination rates in the age group between 45 and 64 years, while in the age group between 0 and 24 years the vaccination rate is lower, as also children and adolescents who have not yet been vaccinated are included in the group. “We compared vaccination scenarios on the curves of confirmed infected, hospitalised treatments, intensive care units and deaths. We performed a comparison for the periods from January 1st, 2021 to June 6th, 2021 and June 1st, 2021 to November 11th, 2021.”

In the following, the analysis refers to “confirmed infected cases” with or to individual, previously mentioned vaccination scenarios or to how the curves of the number of daily confirmed infected cases for the entire pandemic modelling period for all listed scenarios run. The dark blue line shows a full match with the actual situation, while the other scenarios represent differently coloured lines. Of particular interest is scenario S2 (without vaccination), according to which the peak of the epidemic would be reached in August 2021, and the number of infections would reach almost 15 thousand, which coincides with the emergence of the delta strain. A similar but less pronounced scenario is also observed in S3. The peak in this case appears a little later, which is due to vaccination.

The fourth scenario, however, reveals that a new wave of infections does not occur in the autumn, but is postponed to the winter, in early 2022. The case of S4 can also be explained by vaccination. By the beginning of November 2021, it would have reached 70% vaccination coverage, which is predicted to effectively inhibit the rapid spread of the virus among the population. But because vaccination coverage is still lower than that required for collective immunity in the delta version, a new wave appears later than in previous cases. This phenomenon is observed in some other countries in Europe with higher vaccination coverage, where the spread of the virus is also observed, although the vaccination coverage is high. A comparison of the “cumulative number of confirmed cases, with which we want to compare the incidence of virus spread over time and for selected periods” was also performed.

In the second period, a sharp increase in differences is also observed, due to the delta strain. “According to the simulations, the values start to change significantly in the month of August due to the appearance of the delta version and thus a marked increase in the effective reproductive number. This is also reflected in the figures of the total number of confirmed cases for both selected periods”. From the figure above, we can see clear differences in the number of cases in the second period we observe. It is a consequence of the delta strain. In the first period, the effect of vaccination is less noticeable than in the second. This is certainly expected because in the first period we achieved an actual vaccination rate of about 21 percent and in the second about 53 percent. The remaining scenarios operate on the same principle.

In the following, we also touched on the area of “hospital treatment”. The results are presented in the analysis in the same way as in the case of “confirmed cases of infection”. Here, too, we can see a distinct peak, this time shifted to September in the case of the S2 scenario. In the case of this scenario, we would have over 11 thousand hospitalised, which would not be possible in Slovenia. In the S3 scenario, however, the peak is still slightly offset and less pronounced, but even in this case we would have more than 2,500 hospitalisations. Even in this case, we would significantly exceed the capacity of hospitals in Slovenia. In the latter case, however, we would have a negligible number of hospitalisations. “In the case of no vaccination, in the first period we would have on average of 22% higher hospital occupancy per day, in the case of scenario S3 8%, and in the case of scenario S4 5% lower hospital occupancy per day.”

“In the second period, these differences increase markedly, in the case of no vaccination (S2) we would have 15.8 times higher hospital occupancy than the average until November 1st, 2021, in the case of S3 5.0 times, and in the case of higher vaccination coverage (S4) an 85% lower hospital occupancy on average per day.” From the following two graphs we can conclude similarly as before. The number of hospitalisations would increase markedly in the second period under consideration. According to the scenarios the following average numbers of daily receptions would be achieved: 19.1, 267.6, 91.6, and 1.6. It should be noted that anything that exceeds 90 daily admissions also exceeds the capacity of the hospital system in Slovenia. We will also look at the statistics in the field of “Intensive Care Units”. In this case, too, in the case of S2, we would have a pronounced September peak.

The Slovenian healthcare system would not handle the situation with almost 3,000 treatments. In the case of the S3 scenario, we would have over 750 treatments in intensive care units, which also exceeds the capabilities of the Slovenian health care system. In the case of higher vaccination rate than the actual vaccination rate, the burden on intensive care units would be extremely small. The upper limit of occupancy of intensive care units is around 200. In the first period, in the case of non-vaccination, we come closest to this scenario. In that case, we would have 30 percent more hearings than we actually had. In the case of S3, the daily number of hearings would be higher by 13 and lower in the fourth. It is only in the second period, however, that there are huge differences between individual scenarios, as in the case of hospital treatments. In the case of S2 and S3, the capacities allowed by the intensive care units in our country are absolutely exceeded.

“Very important, however, is the number of average readings in the higher vaccination scenario (S4), which relies on only 8.9, which is a practically negligible number compared to the actual situation.” Even when it comes to cumulative curves, the situation is similar to that of hospital treatments. It is very obvious that vaccination has a strong impact on how busy the intensive care units are. In the second period under consideration, the admission of patients increased dramatically. “The number of treatments in intensive care units remains in the same proportions as for admissions to hospital wards. In the first period, the deviations are small, mainly due to the low vaccination rate, and in the second period they increase markedly mainly due to the presence of the delta version.”

“Interestingly, only 51 patients would be treated in this period after the simulation in scenario S4, while we actually treated 657. In the case of scenarios S2 and S3, the admission numbers are unmanageable for our health system.” Even in the case of mortality, a pronounced peak in the case of non-vaccination would be reached in September, according to a 150-day simulation. A less pronounced and more stretched peak would be reached in the case of S3. In this case, there would be 30 deaths a day. However, these numbers would be even higher because hospitals would not be able to deal with such a large number of hospitalisations and intensive care trials, which in turn would lead to even more deaths. “We did not include this in the model in these simulations.”

Cumulative projections show (similar to previous cases) an extremely strong increase in the number of deaths in the second period, where there are large differences in vaccination scenarios. Both numbers and curves clearly indicate that vaccination also significantly reduces covid-19 mortality. 70% vaccination coverage would bring us a relatively low mortality rate in the second period under review – only 45 deaths, compared to 311 deaths in the current situation. Even more worrying scenarios would be S2 and S3.

The key findings of the analysis are: “vaccination greatly influences the course of the epidemic, an appropriate proportion of vaccination can eliminate the occurrence of delta Sars-COV2 virus or shift and flatten key epidemiological curves, without vaccination, Slovenia would have a catastrophic situation due to the delta version and it would be necessary to implement non-pharmacological measures as early as August 2021, 30% lower vaccination than the actual (which means approximately 37% vaccination rate by November 1st, 2021) would overload the health system in September 2021, a 30% higher vaccination than the actual (which means approximately 70% vaccination rate by November 1st, 2021) would nullify the effect of the delta version in Slovenia, as the key epidemiological curves would be significantly lower than today, but would not prevent the fourth wave in full, as this would be postponed to the winter of 2021/2022. Based on the presented analysis, we can therefore conclude that vaccination has a key impact on the course of the covid-19 epidemic in Slovenia and is absolutely necessary to prevent overloading the health care system.”


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