CoVID-19のR0の推定値

LancetでのR0の推定値です。

R0は2.5〜3程度と考えた方が良さそうです。

インフルエンザはR0≒1.3なので、かなり感染力が強いということになります。

麻疹は空気感染することで、R0=13〜17と破格に高いです。

（※　管理者注　2020/04/11記載）

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Lancetに複数の中国でのR0に関する文献（Peer review とPreprintの両方を含む）が出ています。

https://www.thelancet.com/pdfs/journals/langlo/PIIS2214-109X(20)30113-3.pdf

黄色丸が平均値で，赤と青は95%信頼区間の最大・最小値を示す。

発表日順に並べた。左側10個が査読なし。右側6個が査読あり。

査読なしに外れ値が2つあり。合議の上この２つを除外すると，

査読なしで、3.02（95%CI 2.65-3.39）

査読ありで、2.54（95％CI 2.17-2.91）

ということです。

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Journal of Travel MedicineでのR0の推定値です。

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＜議論＞

私たちのレビューでは、平均R0は3.28、中央値は2.79であり、WHOの見積もりである1.4から2.5を超えています。

R0を導出するための確率的および統計的手法を使用した研究は、合理的に比較可能な見積もりを提供します。

ただし、数学的手法を使用した調査では、平均してより高い推定値が生成されます。

数学的に導出された推定値の一部は、統計的および確率的推定値を生成した範囲内にあります。

いくつかの数学的研究によって推定されたより高いR0値の理由をさらに評価することが重要です。

たとえば、仮定のモデリングが役割を果たした可能性があります。最近の研究では、R0は約2〜3で安定しているようです。

後の段階で作成されたR0推定は、より多くのケースデータに基づいて構築され、認識と介入の効果が含まれるため、より信頼性が高いと予想できます。

WHOのポイントの推定値は、公表されているすべての推定値を下回っていますが、WHOの範囲の上限には、ここで検討した推定値の下限が含まれています。

SARSのR0の推定値は2〜5の範囲であると報告されています。これは、このレビューで見つかったCOVID-19の平均R0の範囲内です。

病原体と曝露領域の両方が類似しているため、これは予想されます。

一方、国民の意識の高まりと非常に強力な介入的対応にもかかわらず、COVID-19はすでにSARSよりも広く普及しており、感染性が高い可能性があることを示しています。

＜結論＞

このレビューでは、COVID-19の推定平均R0は約3.28であり、中央値は2.79、IQRは1.16であり、1.95でのWHOの推定値よりもかなり高くなっています。

これらのR0の推定値は、使用される推定方法と、基礎となる仮定の有効性によって異なります。

データが不十分で開始時間が短いため、COVID-19の現在のR0の推定値にはバイアスがかかる可能性があります。

ただし、より多くのデータが蓄積されると、推定誤差が減少することが予想され、より鮮明な画像が形成されるはずです。

これらの考慮事項に基づいて、COVID-19のR0は約2〜3であると予想されます。これは、WHOの見積もりとほぼ一致しています。

The reproductive number of COVID-19 is higher compared to SARS coronavirus

Ying Liu, Albert A Gayle, Annelies Wilder-Smith, Joacim Rocklöv

Journal of Travel Medicine, Volume 27, Issue 2, March 2020, taaa021, https://doi.org/10.1093/jtm/taaa021

Published: 13 February 2020

https://academic.oup.com/jtm/article/27/2/taaa021/5735319?fbclid=IwAR2eimXfMDitS2_sax6ceCwHKYiIGym2prMMwYbpz7MTcbXQKIrCZD0btq4

Introduction

In Wuhan, China, a novel and alarmingly contagious primary atypical (viral) pneumonia broke out in December 2019.

It has since been identified as a zoonotic coronavirus, similar to SARS coronavirus and MERS coronavirus and named COVID-19.

As of 8 February 2020, 33 738 confirmed cases and 811 deaths have been reported in China.

Here we review the basic reproduction number (R₀) of the COVID-19 virus. R₀ is an indication of the transmissibility of a virus, representing the average number of new infections generated by an infectious person in a totally naïve population.

For R₀ > 1, the number infected is likely to increase, and for R₀ < 1, transmission is likely to die out.

The basic reproduction number is a central concept in infectious disease epidemiology, indicating the risk of an infectious agent with respect to epidemic spread.

Methods and Results

PubMed, bioRxiv and Google Scholar were accessed to search for eligible studies.

The term ‘coronavirus & basic reproduction number’ was used.

The time period covered was from 1 January 2020 to 7 February 2020.

For this time period, we identified 12 studies which estimated the basic reproductive number for COVID-19 from China and overseas.

Table 1 shows that the estimates ranged from 1.4 to 6.49, with a mean of 3.28, a median of 2.79 and interquartile range (IQR) of 1.16.

Timeline of the R₀ estimates for the 2019-nCoV virus in China

The first studies initially reported estimates of R₀ with lower values.

Estimations subsequently increased and then again returned in the most recent estimates to the levels initially reported (Figure 1).

A closer look reveals that the estimation method used played a role.

The two studies using stochastic methods to estimate R₀, reported a range of 2.2–2.68 with an average of 2.44.

The six studies using mathematical methods to estimate R₀ produced a range from 1.5 to 6.49, with an average of 4.2.

The three studies using statistical methods such as exponential growth estimated an R₀ ranging from 2.2 to 3.58, with an average of 2.67.

Discussion

Our review found the average R₀ to be 3.28 and median to be 2.79, which exceed WHO estimates from 1.4 to 2.5.

The studies using stochastic and statistical methods for deriving R₀ provide estimates that are reasonably comparable.

However, the studies using mathematical methods produce estimates that are, on average, higher.

Some of the mathematically derived estimates fall within the range produced the statistical and stochastic estimates.

It is important to further assess the reason for the higher R₀ values estimated by some the mathematical studies.

For example, modelling assumptions may have played a role. In more recent studies, R₀ seems to have stabilized at around 2–3.

R₀ estimations produced at later stages can be expected to be more reliable, as they build upon more case data and include the effect of awareness and intervention.

It is worthy to note that the WHO point estimates are consistently below all published estimates, although the higher end of the WHO range includes the lower end of the estimates reviewed here.

R₀ estimates for SARS have been reported to range between 2 and 5, which is within the range of the mean R₀ for COVID-19 found in this review.

Due to similarities of both pathogen and region of exposure, this is expected.

On the other hand, despite the heightened public awareness and impressively strong interventional response, the COVID-19 is already more widespread than SARS, indicating it may be more transmissible.

Conclusions

This review found that the estimated mean R₀ for COVID-19 is around 3.28, with a median of 2.79 and IQR of 1.16, which is considerably higher than the WHO estimate at 1.95.

These estimates of R₀ depend on the estimation method used as well as the validity of the underlying assumptions.

Due to insufficient data and short onset time, current estimates of R₀ for COVID-19 are possibly biased.

However, as more data are accumulated, estimation error can be expected to decrease and a clearer picture should form.

Based on these considerations, R₀ for COVID-19 is expected to be around 2–3, which is broadly consistent with the WHO estimate.

Author contributions

J.R. and A.W.S. had the idea, and Y.L. did the literature search and created the table and figure.

Y.L. and A.W.S. wrote the first draft; A.A.G. drafted the final manuscript. All authors contributed to the final manuscript.

Conflict of interest

None declared.

Teaser: Our review found the average R₀ for COVID-19 to be 3.28, which exceeds WHO estimates from 1.4 to 2.5.