A team of national public health experts and academics from across Europe, including from the MRC Biostatistics Unit, have joined forces to ensure the fight against COVID-19 and its rapidly developing variants continues.  

With decreased testing and sequencing in many countries, now that COVID-19 is no longer defined as a Public Health Emergency of International Concern, international collaborative studies such as this one will become increasingly important for timely assessment of the severity of new, circulating variants. 

A consortium of six countries, led by the WHO/Europe’s Dr Richard Pebody working with Anne Presanis and Tommy Nyberg from the MRC Biostatistics Unit (BSU), has produced and piloted a standardised COVID-19 severity protocol and accompanying statistical code.  

“During the spring and summer of 2022, mass testing for COVID-19, as well as sequencing capacity, was reducing in many countries as the pandemic appeared to recede. As data on cases and the virus variants become less available, collaborative international efforts to understand the severity of new, emerging variants will become more important,” explains Dr Pebody, Programme Area Manager for Infectious Hazards at the WHO Regional Office for Europe.”  

“Such collaborations can provide larger effective sample sizes than those available in single-country datasets, which may enable more rapid identification of differences in virulence between virus variants,” he adds. 

Tommy Nyberg, Research Associate at the BSU, says:

“The final protocol and code allows investigators in individual countries to analyse their nationally available cohort data on COVID-19 cases whose infecting variant is known to estimate their risk of outcomes such as hospital admission, intensive care unit admission, or death. 

The results from these consistently conducted analyses can then be directly compared, combined, and pooled using meta-analysis methods, which allows for estimates based on larger effective sample sizes than estimates based on data from a single country.

To assess feasibility, the protocol and code was applied separately by investigators from six countries to data from late 2021, when Omicron BA.1 emerged and replaced Delta as the dominant SARS-CoV-2 variant,” explains Dr Nyberg. 

Consistent with findings from previous studies, this investigation revealed that for cases infected with Omicron BA.1 compared to Delta the risk of hospital admission was on average 59% lower, the risk of admission to intensive care unit was 88% lower, and the risk of death was 69% lower.” 

Anne Presanis, Senior Statistician at the BSU says:

“There was considerable variation in the countries’ results. In all countries Omicron BA.1 appeared to cause less severe illness than Delta, but the estimated difference in risk between cases infected with Omicron BA.1 or Delta was found to be both considerably smaller or greater than the average, depending on the country.  

However, some heterogeneity between countries might be expected, and might reflect differences in outcome definitions or in testing and vaccination policies and implementation,” she adds. 

The joint working group was set up between the WHO Regional Office for Europe and the European Centre for Disease Prevention and Control (ECDC) and includes public health agencies and academic collaborators in six European countries (Denmark, England, Luxembourg, Norway, Portugal, and Scotland.) 

Read full paper here: Eurosurveillance | A standardised protocol for relative SARS-CoV-2 variant severity assessment, applied to Omicron BA.1 and Delta in six European countries, October 2021 to February 2022