Effect of contact networks on SARS-CoV-2 transmission and control

The emergence of the highly communicable Delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has compelled scientists to analyze the risk created by the increased social contacts, primarily in large-scale events as various countries have withdrawn the pandemic restrictions. With the increase in mass immunity against SARS-CoV-2 due to vaccination drives, various countries are moving back to their pre-pandemic life. Various revenue-generating activity settings like conferences, exhibitions, meetings, and cruises pose a high risk of contact rates, leading to an outbreak.

Study: Using high-resolution contact networks to evaluate SARS-CoV-2 transmission and control in large-scale multi-day events. Image Credit: WESTOCK PRODUCTIONS/ Shutterstock

Therefore, the event planners need to have some interventions to safely resume their activities, which also helps policymakers maintain a balance between public health and economic gains. Since there have been reports of the SARS-CoV-2 Delta variant infecting vaccinated individuals, many countries are using rapid antigen tests, mask mandates, vaccine certifications, and digital contact tracing devices along with routine vaccination to mitigate viral transmission.

A study recently published on the medRxiv* preprint server demonstrated that the social contacts created in different activity settings affect interventions needed to control outbreaks.

Assessment of social contact data to simulate SARS-CoV-2 Delta variant outbreaks

During the coronavirus disease 2019 (COVID-19) pandemic, ‘cruises to nowhere’ were the safest alternative to travel in Singapore, where different activities and setting-specific interactions were planned. The researchers collected the contact data from around 1,000 crew and 1,300 passengers per sailing between November 2020 and 13 February 2021 and assessed the subsequent social interaction networks. These contact networks were used to simulate SARS-CoV-2 Delta variant outbreaks and analyze the impact of different combinations of interventions and network formulations on transmission in different settings during a large gathering.

Throughout the study, cruises were operating at half the capacity of passengers and crew members. It was also mandatory to maintain a physical distance of at least one meter among different travel groups. The following interventions were included during the study: (i) one-off PCR testing a day before sailing, (ii) rapid antigen testing at the beginning and middle of the event, (iii) mask mandates in possible settings, and (iv) vaccination coverage among participants.

Significance of using a combination of interventions

The data from the study show that 25 passengers had a median of 20 unique close contacts per day, and more than 60% of their contact episodes happened in sports or dining areas where mask mandate was not applicable. The researchers observed in simulated outbreaks that rapid antigen tests and large vaccination exposure had a greater impact than the mask obligation alone, representing the significance of combined interventions against the Delta variant to minimize the risk of an outbreak.

The researchers observed that mask-free activities and faulty testing protocols could lead to a wide range of contacts with unidentified infectious individuals over a multi-day cruise, leading to a major outbreak in different settings. This social network analysis showed that passengers had several contacts who had a high number of contacts with other individuals.

Above 70% close and casual contacts were noted in food and beverages locations where the risk of infection and transmission was high due to mask-off rules and limited space. Observations from the study showed that none of the interventions analyzed were individually capable of minimizing the outbreak. All the interventions would work together to reduce the risk of infection and transmission.

Limitations of the study

The model failed to design contact tracing around detected cases. Also, the study did not consider fully asymptomatic infections. Furthermore, the passengers were instructed to carry the contact tracing devices at all times except when involved in water sports which precludes the proper representation of interactions at the water sports areas. However, the impact of this factor is very minimal in the study. Lastly, since the passenger’s device may be placed in a 2m proximity in a cabin, recording frequent close contact interactions in these settings may not be done perfectly.

*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

Written by

Susha Cheriyedath

Susha has a Bachelor of Science (B.Sc.) degree in Chemistry and Master of Science (M.Sc) degree in Biochemistry from the University of Calicut, India. She always had a keen interest in medical and health science. As part of her masters degree, she specialized in Biochemistry, with an emphasis on Microbiology, Physiology, Biotechnology, and Nutrition. In her spare time, she loves to cook up a storm in the kitchen with her super-messy baking experiments.