Hospitals in Okinawa have been facing outbreak of the coronavirus disease 2019 (COVID-19) because of its pandemic spread. 1 Although the outbreak has still been in the early phase in Okinawa, it would become serious factor related to healthcare collapse to have insufficient supply of intensive care unit beds and ventilators to care the rapidly growing number of critically ill patients with Okinawa is a group of small remote islands having no industry that could rapidly produce ventilators 3 ; it may require several days of shipping time for importing ventilators. Thus, we estimated the number of ventilators and noninvasive ventilators that would be required in Okinawa at the peak of the COVID-19 outbreak to address the intensive care preparation. Our estimates are based on recent data of COVID-19 cases in Okinawa and data on the proportion of patients with COVID-19 in the ICU requiring ventilation.
We used the well-known SEIR epidemic model. 4 The meaning and value of each parameter are shown in Table 1 . We regard t = 0 as of February 14, 2020, which is the day when the first COVID-19 case was confirmed in Okinawa. 13 Thus, Y(0) = 1, and hence, I(0) = Y(0)/ (pN) ≈ 8.62 ×10 −6 . For simplicity, we assume that E(0) = R(0) = 0, and thus, S(0) = 1 -I(0) ≈ 1. The basic reproduction number R 0 14 is calculated as R 0 = β/γ ≈ βS(0)/γ.
To estimate the infection rate β, we apply the least-squares-based method 4 to the data of the daily confirmed cases of COVID-19
in Okinawa from February 14 to April 30, 2020. As a result, we obtain the estimated value β = 0.14 (95% CI, 0.12-0.16), and thus, 
Proportion of susceptible population -0-1 Estimated E(t) Proportion of exposed population -0-1 Estimated requiring invasive (resp. noninvasive) ventilation is r 1 = 0.39 (resp. r 2 = 0.31). 11 Thus, the number of required invasive (resp. noninvasive) ventilators can be calculated by multiplying r 1 q (resp. r 2 q) by the number Y(t) of confirmed patients. That is, V 1 (t) = r 1 qY(t) and
V 2 (t) = r 2 qY(t).
Using the parameters in Table 1 , we obtain the estimation of the epidemic curve of COVID-19 in Okinawa as shown in Figure 2 .
As of April 30, 2020, it seems that the epidemic in Okinawa is well controlled and the estimated epidemic curve is sufficiently flattened so that the peak comes late (t = 413, ie, April 2, 2021).
However, if it goes to the worse scenario (β = 0.16 and R 0 = 1.6), then the peak would come within this year (t = 304, ie, October 14, 2020) and the number of confirmed cases at the peak (≈6334) would become about 1.8 times larger than that for the baseline scenario (≈3532).
We obtain the estimation of the number of required ventilators for COVID-19 in Okinawa as shown in Figure 3 . There is a margin of available ventilators even at the peak in the worse scenario (β = 0.16
and R 0 = 1.6). for patients with severe disease in Japan, we may face the greater number of patients with both mild and severe diseases. 17 Second, the pandemic might subside from specific climate conditions in Okinawa such as higher temperature and humidity along with ultraviolet radiation exposure in summer. 18 Third, the coinfection of COVID-19 and influenza in winter may lead to higher incidence of severity, which may increase the demand. 19 In conclusion, although it would be disastrous to wait and see until the possible supply shortage of life-saving ventilators, the requirement of ventilators would not exceed its availability during the period of expected peak based on our estimate about the highest demand scenario. Urgent actions conducted in Okinawa would save lives and avoid devastating rationing that would require physicians not to be able to allocate ventilators to some of patients with COVID-19.
None.
The authors have stated explicitly that there are no conflicts of interest in connection with this article. 