Using Mathematical Models to Assess Responses to an Outbreak of an Emerged Viral Respiratory Disease

6.2 How many courses of antivirals are needed for health care workers

Page last updated: April 2006

The role of health care workers (HCWs) will be an important one in several ways during a pandemic. During the early stages, in which elimination of the outbreak is likely to be attempted, various interventions will be needed and HCWs are likely to be involved and subject to exposure in most of these. Antivirals will need to be used for the prophylaxis of health care workers engaged in the implementation of these interventions.

In the early stages of the outbreak, the outbreak will be localised within a small number of regions in Australia. This makes it likely that only a relatively small number of health care workers will need to be taking prophylaxis initially, but that as the number of cases grows large, a greater fraction of the health care workforce will need to receive prophylaxis. Here we model this growth in the number of health care workers requiring prophylaxis in a simple way by assigning a set number of antiviral courses for health care workers’ prophylaxis for each new infectious case.

Effects of four strategies for targeted use of  the AV stockpile for community members on (a) the cumulative use of AVs by HCWs  over time and (b) the number of infectives over time for an epidemic with a 70%  attack rate

Figure 6.3  Effects of four strategies for targeted use of the AV stockpile for community members on (a) the cumulative use of AVs by HCWs over time and (b) the number of infectives over time for an epidemic with a 70% attack rate in the absence of intervention. The strategies are (i) no AV use, (ii) 50% of cases treated, (iii) 40% of patient contacts prophylaxed, and (iv) 50% of patients treated as well as 40% of patient contacts prophylaxed.

As an example, consider an epidemic which without intervention would lead to an attack rate of 70% and where for each new infective, 5 courses of antiviral drugs would need to be distributed to health care workers, up to the point at which half of the entire health care workforce is placed on prophylaxis (we describe this as a dynamic distribution of AVs). On the basis of these assumptions, the use of AVs by health care workers over the course of an epidemic can be calculated. If AVs are also used to treat a proportion of cases and to prophylax a proportion of case-contacts, then the number used by health care workers will change.

In Figure 6.3(a) we show the use of antiviral courses by HCWs over time for four different strategies of stockpile use, namely using AVs

(i) for HCW prophylaxis only,

(ii) for HCW prophylaxis and to treat 50% of cases,

(iii) for HCW prophylaxis and for prophylaxis of 40% of case contacts, and

(iv) for HCW prophylaxis, to treat 50% of cases and for prophylaxis of 40% of case contacts.

Figure 6.3(a) shows the number of infectives over time for each of these strategies. The amount of the stockpile remaining after 3, 6, 9 and 12 months for these strategies is presented in Table 6.1. These results were generated using the contact-tracing model depicted in Figure 5.7.

If the stockpile is used only to prophylax health care workers, then for this example more than half the stockpile remains after the epidemic has passed, but this has no effect on the course of the epidemic. If 50% of cases are also treated, then the stockpile runs out 4-5 months after the start of the epidemic, and the peak of the epidemic is smaller and delayed by about 1 month. If contact tracing is employed and 40% of case contacts are prophylaxed throughout the course of the epidemic, then the stockpile runs out between 6 and 7 months and the peak of the epidemic is delayed by more than 4 months. Finally, if both treatment and prophylaxis of cases are conducted in addition to protecting HCWs, then the stockpile will last for 10-11 months and the peak of the epidemic will be delayed by at least 8 months.

  No community use 50% of cases treated 40% of case contacts prophylaxed 50% treatment and 40% prophylaxis
Time (months) AVs left
  (mil)
AVs used for HCWs
(mil)
AVs left
(mil)
AVs used for HCWs
(mil)
AVs left (mil) AVs used for HCWs
(mil)
AVs left (mil) AVs used for HCWs
(mil)
3
3.50
0.5
3.6
0.37
3.9
0.0220
3.97
0.0097
6
2.30
1.7
0
0.95
1.9
0.58
3.75
0.076
9
2.10
1.9
0
0.95
0
0.81
2.41
0.483
12
2.10
1.9
0
0.95
0
0.81
0
1.07

Table 6.1   Amount of the AV stockpile remaining, and the number of courses used to protect HCWs at 3, 6, 9 and 12 months after the start of the epidemic for the four strategies of community AV use described in the text.

These results might appear counter-intuitive in the sense that by using AVs for community intervention, the number of courses required for HCWs is reduced. The reason for this is that the courses are being distributed to health care workers in proportion to the number of new infectious cases. Since the epidemic peak is delayed and reduced in size by community use for prophylaxis and treatment, there is less use of AVs over time than in the results presented in Table 5.2. A second factor is that the stockpile eventually runs out when used for community treatment and prophylaxis and after that point is no longer available to protect health care workers. This also has the effect of reducing the cumulative use of the stockpile for protection of health care workers.

These results assume that the community prophylaxis and treatment will continue to be used until the stockpile runs out. It would not be difficult to design a strategy that switched from this approach to one of maintaining services at a time that ensured enough courses of AVs remained to protect health care workers through the entire epidemic.


Document download

This publication is available as a downloadable document.

Using Mathematical Models to Assess Responses to an Outbreak of an Emerged Viral Respiratory Disease(PDF 873 KB)