The recent research paper “Serial Interval of SARS-CoV-2 was Shortened Over Time by Non-pharmaceutical Interventions” suggests that China’s successful management of the serial interval helped it suppress the spread of Covid-19. This strategy has now resulted in over a month without any local cases in the country.
Understanding the Serial Interval Concept
In epidemiology, the serial interval refers to the period between the onset of symptoms in a primary case and the subsequent cases that this primary case generates. Simply put, it measures the time gap between when Person A starts showing Covid-19 symptoms and when Person B, who was infected by Person A, begins to exhibit symptoms as well.
The serial interval terminology originated from British physician William Pickles during a UK hepatitis epidemic between 1942-45. It was initially called the transmission interval. The term ‘serial interval’ was later adopted by another British physician, RE Hope Simpson, to denote the timeline between successive illness onsets.
This metric depends on other key epidemiological parameters, like the incubation period (which is the timeframe between exposure to the virus and the first symptoms) and the reproduction rate (or R nought), which is the number of people an infected individual can infect.
The Role of Serial Interval in Controlling Covid-19
The serial interval is instrumental in assessing the efficacy of infection control interventions. Beyond this, it also provides indications about population immunity levels and aids in forecasting future disease incidence. This implies that reducing the serial interval by quickly identifying and isolating those contracting Covid-19 can decrease virus transmission opportunities.
To effectively manage the serial interval, a solid system comprising contact tracing, quarantine, and isolation protocols is paramount.
Cases of China and South Korea: Serial Interval Management
In both China and South Korea, aggressive management of the serial interval played a crucial role in controlling the spread of Covid-19. For instance, in Wuhan, China, the serial interval decreased from 7.8 days to just 2.6 days between early January and February. This substantial reduction was achieved through rigorous measures, such as quarantining contacts within one day from the onset of symptoms, which slashed transmission by 60%.
In a similar vein, South Korea achieved an estimated serial interval of merely 3.63 days. Both these countries’ success stories can be attributed to their emphasis on rigorous contact tracing, quarantine, and isolation measures. Such proactive steps ensured that infected individuals couldn’t infect many more people later in the infection cycle.
Additional non-pharmaceutical interventions, like suspending intra- and inter-city travel and various forms of social distancing, also contributed to keeping the serial interval low across these nations.
Therefore, it appears that controlling the serial interval could be key in managing the transmission of diseases like Covid-19 and potentially curtailing future outbreaks.