A Swedish study published within the journal Emerging Infectious Diseases observes a high prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron infection despite greater than 80% seroprevalence in Sweden.
Study: High Prevalence of SARS-CoV-2 Omicron Infection Despite High Seroprevalence, Sweden, 2022. Image Credit: ibrahimbeyy / Shutterstock
The coronavirus disease 2019 (COVID-19) pandemic brought on by SARS-CoV-2 has created tremendous healthcare and socioeconomic damage worldwide, with greater than 765 million infections and over 6.9 million deaths registered to the World Health Organization (WHO).
Probably the most recently emerged omicron variant of SARS-CoV-2 has shown significantly higher transmissibility and infectivity in comparison with other variants of concern (VOCs) with improved viral fitness which have emerged in the course of the pandemic.
Due to high percentage of mutations within the spike receptor binding domain (RBD), omicron has gained high immune evasion potency, causing breakthrough infections and reinfections worldwide despite preexisting anti-SARS-CoV-2 immunity developed by COVID-19 vaccination or natural SARS-CoV-2 infection.
In Sweden, general polymerase chain response (PCR) testing for COVID-19 has been suspended in early 2022. Currently, the country largely is dependent upon point prevalence surveys which can be conducted to detect acute SARS-CoV-2 infections by PCR and former infections by serological testing.
In the present study, scientists have conducted two cross-sectional surveys during 2022 to estimate COVID-19 point-prevalence and overall seroprevalence in Sweden.
Two surveys covering 21 and 11 regions in Sweden were conducted in March and September, respectively. The participants representing 64% of the Swedish population, were supplied with appropriate kits and related instructions for self-sampling at home.
Within the March survey, a complete of two,906 individuals (age range: 2 – 96 years) were enrolled. Within the September survey, a complete of 1,774 individuals (age range: 2 – 94 years) were enrolled.
The purpose prevalence of COVID-19 within the Swedish population was estimated to be 1.4% at the top of March. All detected infections were brought on by omicron subvariants except one which was brought on by delta variant.
Amongst participants tested for ongoing infection, 24% had previously reported SARS-CoV-2 infection and 79% had received a minimum of three doses of COVID-19 vaccine. Amongst participants who tested positive for SARS-CoV-2, about 8% had previously reported SARS-CoV-2 infection.
The evaluation of anti-spike antibody levels in participants revealed a seroprevalence of 93% within the Swedish population at the top of March. Amongst participants aged below 11 years and above 11 years, the estimated seroprevalences were 80% and 94 – 98%, respectively.
Within the September survey, the purpose prevalence was estimated to be 1.5%. All detected infections were brought on by omicron subvariants.
Amongst participants tested for ongoing infection, 29% had previously reported SARS-CoV-2 infection and 85% had received a minimum of three doses of COVID-19 vaccine. Amongst participants who tested positive for SARS-CoV-2, about 71% had previously reported SARS-CoV-2 infection.
The seroprevalence within the Swedish population was estimated to be 93% at the top of September. Amongst participants aged below 11 years and above 11 years, the estimated seroprevalences were 84% and 84 – 100%, respectively.
Regarding symptoms, about 65% and 67% of the participants from the March and September surveys, respectively, reported a couple of symptom inside two weeks before sampling.
The study reveals that roughly 1 in every 66 individuals in Sweden was infected with SARS-CoV-2 by March and September 2022. Almost all the detected infections were brought on by omicron subvariants. Furthermore, the study reveals that the estimated seroprevalence within the Swedish population was greater than 80% in the course of the same period.
Overall, the study findings indicate that current COVID-19 vaccines provide only limited, short-term protection against omicron breakthrough infections. Similarly, a high level of reinfections observed within the study indicates that omicron subvariants are able to evading not only vaccine-induced immunity but additionally infection-induced immunity.
Considering the high transmissibility of omicron subvariants despite high vaccine coverage, the scientists highlight the necessity for continuous monitoring of the overall population for the detection of newly emerging and possibly more pathogenic viral variants.