This figure shows historical Rt estimates. When the Rt increased to 1.0 and subsequently to 1.05 it signaled the onset of the winter wave in both 2022 and 2023. Notably, the timing of the winter wave’s onset was similar in 2022 and 2023 but occurred later for 2024. In 2024, the Rt reached 1.0 on Oct 26 but did not exceed 1.05
The Effective Reproductive Number, shown here as “Rt” helps us understand how fast COVID-19 is spreading in our community. For COVID-19, Rt tells us the average number of people who will contract this disease from each infected person.
For example, if Rt equals 1, each existing infection causes one new infection. An Rt equal to 1 means the disease will stay present and stable in our community.
If Rt is less than 1, each existing infection causes less than one new infection. Therefore, if Rt stays below 1, spread of the disease declines and it eventually leaves the community.
When Rt is more than 1, each existing COVID-19 infection causes more than one new infection. The disease will be transmitted between more and more people and the spread of the disease is growing. If Rt stays greater than 1, it can lead to many challenges, including hospitals not being able to care for everyone who gets sick.
Rt depends on people’s behavior, like wearing a mask or keeping social distance. This is why Rt can change over time.