Experts Weigh In on the Rising Rt and Its Implications for the Country’s Pandemic Response
Singapore is currently facing a growing concern as its COVID-19 reproduction rate, known as Rt, exceeds 1, signalling a potential surge in cases. On September 6, Lawrence Wong, co-chair of Singapore’s COVID-19 multi-ministry task force, highlighted that while case numbers are important, the rate at which the virus spreads—also known as the reproduction number—was of greater concern. He warned of an “exponential rise” in cases, with projections suggesting that daily cases could reach 1,000 within two weeks, or even 2,000 within a month, if the trend continues.
Understanding the Reproduction Number (R)
The reproduction number, or R, represents the average number of people an infected individual will pass the virus on to. It is crucial for understanding the pace of the pandemic. There are two types of R numbers: R0 (basic reproduction number) and Rt (effective reproduction number). R0 refers to the number of cases one infected person could cause in a fully susceptible population, while Rt reflects the virus’s spread considering factors such as immunity and control measures.
Experts note that Singapore’s Rt currently stands at around 1.5, meaning that for every two people infected, three others are becoming infected. This reflects the ongoing exponential rise in cases, and during the previous period of heightened alert, Rt had fallen below 1, which is considered ideal for curbing the virus’s spread.
Should We Be Concerned About R?
While the R number is a valuable tool for understanding the virus’s spread, some experts argue that it may become less significant as COVID-19 becomes endemic. Professor Paul Tambyah, president of the Asia Pacific Society of Clinical Microbiology and Infection, noted that the R0 for seasonal flu is around 1.4 and doesn’t usually provoke much concern, suggesting that society might tolerate a similar level of spread with COVID-19.
Professor Dale Fisher, a senior consultant at the National University Hospital, agreed that Rt would eventually become “irrelevant” if Singapore shifts away from mass testing and case counting. However, he emphasised that for now, maintaining a lower Rt is essential to prevent a rapid escalation of cases and ensure that the healthcare system can manage the increase.
Factors Behind the Rise in Rt
The more infectious Delta variant has played a significant role in increasing both R0 and Rt. Associate Professor Alex Cook, an expert in infectious disease modelling, explained that the Delta variant has likely doubled the reproduction rates, making it more challenging to control the virus’s spread. Additionally, the increase in socialising after restrictions were eased and the waning protection against infection from vaccinations may also have contributed to the rise in Rt.
What Does a High Rt Mean for COVID-19 Restrictions?
If Rt continues to rise, experts warn that a majority of the population could become infected, even with high vaccination rates. However, the majority of these cases would likely be mild. As Rt approaches higher levels, the government may need to implement additional measures to bring it back down to manageable levels.
Professor Tambyah suggested that a high Rt could support the government’s decision to ease restrictions, with a focus on protecting vulnerable populations and ensuring a functioning healthcare system. The idea would be to shift towards learning to live with the virus, similar to how society manages seasonal influenza.
Can Rt Be Reduced?
To reduce Rt without reverting to heightened alert measures, experts propose several strategies, including booster vaccinations, increased use of self-testing, and enhanced public health measures such as mask-wearing and social distancing. However, Professor Tambyah believes that maintaining current guidelines and ensuring the vulnerable are vaccinated could be sufficient to manage the situation.
Ultimately, Professor Ooi Eng Eong from Duke-NUS Medical School stated that Rt may not fall below 1 for the foreseeable future. The key, he said, is societal acceptance and the willingness to tolerate a certain level of transmission as the country opens up and adjusts to living with COVID-19.
