Modeling study shows importance of contact tracing in preventing COVID-19 transmission

The coronavirus disease 2019 (COVID-19) vaccines are the best way to reduce the risk of severe infection with the severe acute respiratory syndrome 2 (SARS-CoV-2) virus. But the vaccines are not a panacea. Until there is high vaccination worldwide, other COVID-19 prevention strategies such as contact tracing are needed to thwart the transmission of SARS-CoV-2 variants.

In the face of rising vaccination rates, untraced cases may increase the number of COVID-19 cases. A new study led by Choo-Yee Ting from Multimedia University in Malaysia found that contact tracing remains an important tool in mitigating coronavirus spread and subsequent infection.

The researchers write:

While vaccination rates have progressively increased in Malaysia and some parts of the world, efficient contact tracing must be rapidly implemented to reach, find, test, isolate, and support the affected populations to bring the pandemic under control.”

The study “Vaccines alone are no silver bullets: a modeling study on the impact of efficient contact tracing on COVID-19 infection and transmission” is published on the medRxiv* preprint server.

How they did it

The researchers created a simulation based on the available Malaysian COVID-19 data to evaluate how effective contact tracing helps mitigate COVID-19 transmission and infection in a country with high vaccination rates. They modeled the number of untraced symptomatic and asymptomatic COVID-19 cases in the population.

Future work should focus on simulating the effect of contract tracing while taking into account the severity of COVID-19 illness and the current state of the country’s healthcare system.

Increased contract tracing with high vaccination rates lowered untraced, asymptomatic cases

When Malaysia had approximately 30% contact tracing with a rate of 450,000 vaccines doses administered per day, there would be a peak of 1.52 million asymptomatic cases by day 42. However, increases in contact tracing reduced the number of asymptomatic cases.

When contact tracing increased to 70%, it took longer for asymptomatic cases to reach their peak. The highest number of daily cases would be 459,000 — 70% fewer cases than if there was only 30% contact tracing.

Having about 90% contract tracing effectiveness nearly flattened the curve.

Increased contract tracing with high vaccination rates reduced untraced, symptomatic cases

Increasing contact tracing delayed and decreased peaks of untraced, symptomatic cases.

Combining high vaccination levels and 30% effectiveness in contract tracing simulated resulted in a peak of 3.5 million untraced, symptomatic cases by day 40. Increasing 70%, effective contact tracing efforts delayed the peak by approximately 15 days.

Effects of high contract tracing and low vaccination rates

Low vaccination rates with 90% contract tracing result in a peak of 182,000 COVID-19 cases by day 74. Similar trends were observed among symptomatic cases.

Having a 1% vaccination rate with 90% contact tracing delayed the peak number of cases to day 72. In this scenario, the peak was 381,000 COVID-19 cases.

The researchers also modeled the effect of 90% contact tracing with vaccination rates ranging from 0.8% to 1.4% per day. Results showed the peak number varied from 107,000 to 207,000 COVID-19 cases. The peak occurred from day 68 to day 73.

Increasing vaccination rates did not lower the peak number of cases. However, having more vaccines administered per day delayed the peak number of COVID-19 cases.

Low vaccination rates and 90% contact tracing reduced the number of untraced, symptomatic cases to about 381,000 by day 70. In untraced, asymptomatic cases, the model estimated about 540,000 cases by day 57 when vaccination rates were 1.4%.

Given the significance of contact tracing in pandemic control, it is pivotal to capitalize the contacts data, automate the data processing and application process, and develop more efficient strategies to improve contact tracing effectiveness,” wrote the research team.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Jocelyn Solis-Moreira

Written by

Jocelyn Solis-Moreira

Jocelyn Solis-Moreira graduated with a Bachelor's in Integrative Neuroscience, where she then pursued graduate research looking at the long-term effects of adolescent binge drinking on the brain's neurochemistry in adulthood.

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