Study shows several low- and middle-income countries at over 50% risk of undetected Omicron transmission

In a recent study posted to the medRxiv* pre-print server, a team of researchers estimated the probability of undetected emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant in 25 low and middle-income countries (LMICs) by early December.

Study: The risk of SARS-CoV-2 Omicron variant emergence in low and middle-income countries (LMICs). Image Credit: Eve Orea/ShutterstockStudy: The risk of SARS-CoV-2 Omicron variant emergence in low and middle-income countries (LMICs). Image Credit: Eve Orea/Shutterstock

The SARS-CoV-2 Omicron variant (B.1.1.529) was identified first in South Africa on 26 November 2021, and by December 2021, coronavirus disease 2019 (COVID-19) infections due to Omicron were reported in over 40 countries.

The LMICs included in the study have very few direct flights from South African countries, where Omicron was initially detected. Yet, many of these countries have enacted stricter border policies to reduce Omicron importation risks from South Africa. Nevertheless, there is a substantial possibility of Omicron importation in LMICs from international destinations other than South Africa.

Given the lower capacity for COVID-19 testing, vaccination, and medical treatment in LMICs, Omicron importation would have much more devastating public health outcomes in these countries than in high-income countries.

About the study

In the present study, the researchers analyzed the risks of the Omicron importation in 25 LMICs across Asia, Europe, and North and South America.

The following LMICs were included in the study - Bangladesh, Nepal, Pakistan, Bhutan, Paraguay, Turkey, Serbia, Bolivia, Argentina, Uruguay, Philippines, Colombia, Egypt, Indonesia, Albania, Jordan, Panama, Dominican Republic, Ecuador, Peru, Jamaica, Honduras, Guatemala, Costa Rica, and El Salvador.

The researchers estimated the daily travel volume to each LMIC from 13 developed countries where Omicron had been detected. Based on the assumption that only 2.5% of Omicron cases were identified and reported, they also estimated the prevalence of Omicron in the 13 Omicron-detected countries (ODCs). Lastly, they estimated the probability of Omicron introduction into each LMIC by 5 December 2021 due to a traveler from ODCs.

Based on reported COVID-19 vaccination levels in LMICs, estimates of immunity acquired by previous SARS-CoV-2 infection, and the transmissibility and immunity evading capabilities of Omicron, the researchers also estimated the effective reproduction number of Omicron in each LMIC to assess the risk of Omicron transmission following importation.

Findings

Of the 25 studied LMICs, six countries had over 50% chance of receiving at least one Omicron importation from someone traveling from ODCs by 5 December 2021.

Serbia and Turkey, the European LMICs, which are highly connected to Western European countries by flights and other modes of transport, were at the highest estimated risks and reported Omicron cases by November 2021. The estimated risk was high for Asian LMICs such as Pakistan, Bangladesh, and Nepal. They had travelers from the UK, India, and those halting there during connecting flights. Colombia, Dominican Republic, and Paraguay were among the American LMICs at risk for Omicron importations from the USA and Brazil.

In the absence of public health interventions, and given the low vaccination coverage and high infectivity of Omicron, the estimated Re of Omicron on 5 December 2021, across the 25 studied LMICs was in the range of 7.0 to 9.4, which is double the reproduction number (Ro) of the Delta variant, which created havoc during the second wave of COVID-19 pandemic. Less than 50% efficacy of COVID-19 vaccines against Omicron makes these findings more worrisome.

Conclusions

LMICs are at heightened risk of Omicron importations from several international destinations, in addition to South Africa, where Omicron emerged in late 2021.

Combined estimates of Omicron importation and transmission risks showed a probability of undetected Omicron transmission in LMICs by early December. Among the LMICs evaluated in the present study, the estimated risk of Omicron transmission was over 99% in three countries - Turkey, Pakistan, and Serbia - with transmission risks of 99.99%, 99.95%, and 99.81%, respectively. Nepal, Bangladesh, and the Dominican Republic, with the estimated transmission risks of 87.98%, 84.86%, and 82.21%, respectively, were also at high estimated risks of Omicron transmission. Further, in nine other LMICs, the Omicron transmission risk exceeded 50%. Overall, these analyses suggested that Omicron-like SARS-CoV-2 variants can rapidly emerge in LMICs and continue to spread for weeks undetected.

Due to the high socio-economic costs associated with the implementation of travel restrictions and using non-pharmaceutical interventions, many of the LMICs may not be able to take measures to prevent Omicron introductions or slow down its spread. Nevertheless, based on the study estimates, the authors suggested that implementing NPIs in LMICs would cut down Omicron transmission by 80%, reducing the probability of its undetected emergence from 12.02% to 80.77% across all the 25 LMICs.

*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:
Neha Mathur

Written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She has a Master’s degree from the University of Rajasthan with a specialization in Biotechnology in 2008. She has experience in pre-clinical research as part of her research project in The Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ programming.

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