In a recent study published in JAMA Network Open, researchers estimate the proportion of Icelandic residents reinfected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant of concern (VOC).
Study: SARS-CoV-2 reinfection rate during an Omicron wave in Iceland. Image credit: angellodeco / Shutterstock.com
background
Coronavirus disease 2019 (COVID-19) was declared a global pandemic on March 11, 2020. SARS-CoV-2 Omicron COV, which is currently the dominant circulating strain worldwide, has characteristics of immuno- higher evasions compared to previous VOCs, thereby increasing the likelihood of re-infection by SARS-CoV-2.
The relative immune protection induced by previous SARS-CoV-2 infection against reinfection with Omicron VOC has been reported to be 56% compared to 92% for VOC Delta reinfections. However, the risk of reinfection with Omicron VOC at the population level needs further investigation.
About the study
In the current population-based cohort study, researchers estimate the risk of SARS-CoV-2 reinfection with Omicron VOC in Iceland.
Individuals with a history of SARS-CoV-2 infection were assessed for the development of reinfection during the period of Omicron dominance in Iceland. To this end, the current study was conducted between 1 December 2021, which was the date of the first reported case of Omicron among Icelandic residents, and 13 February 2022, which is when the study ended.
The researchers obtained data on the status of COVID-19 vaccines and previous SARS-CoV-2 positive reverse transcription-polymerase chain reaction (RT-PCR) analysis reports for the your analysis
A person was considered to be reinfected with SARS-CoV-2 if they tested positive for COVID-19 by RT-PCR more than 60 days from the initial SARS-CoV-2 positive RT-PCR result. Logistic regression models were used to estimate the proportion of SARS-CoV-2 reinfections as a function of days since previous RT-PCR positive reports for SARS-CoV-2, age of participants, and status of vaccinations against COVID-19, and the calculated odds (OR).
Results of the study
A total of 11,536 RT-PCR confirmed cases of COVID-19 were considered for analysis. The average age of study participants was 34 years, 51% of whom were male. About 26% of study participants had received at least one dose of a COVID-19 vaccine.
The median number of days since the initial positive RT-PCR test result for SARS-CoV-2 was 287 days. SARS-CoV-2 reinfections were reported in 12% of individuals during the period of Omicron dominance.
Among participants who had received at least one dose of the COVID-19 vaccine, 12% were reinfected with SARS-CoV-2. This was comparable to 11% who had received at least two doses of the COVID-19 vaccine. The reinfection rate was highest at 15% among people aged 18-29, with fewer reinfections seen among older people.
The odds of reinfection with SARS-CoV-2 were proportionally higher with days since previous SARS-CoV-2 infection, with an OR of 1.6 for 18 months compared with three months. In addition, the risk of reinfection was greater among individuals who had received at least two doses of vaccine compared with those who had received one dose of vaccine with an OR of 1.4.
Conclusions
The results of the study showed that a considerable proportion of individuals developed SARS-CoV-2 reinfections in the initial 74 days of Omicron prevalence in Iceland, with the highest rate of reinfections observed among individuals 18 at 29 years old A directly proportional correlation was observed between the probability of reinfection and the number of days since previous SARS-CoV-2 infections.
Unexpectedly, two or more vaccine doses were associated with a slightly higher likelihood of reinfection compared with one or fewer vaccine doses.
The study’s findings should be interpreted with caution, as the study had several limitations. These include a lack of adjustment for composite associations between prior SARS-CoV-2 infections, eligibility criteria for COVID-19 vaccination, and the presence of underlying medical conditions.
As of December 1, 2021, everyone 12 years of age and older was eligible to receive two doses of the COVID-19 vaccine at no charge. At this time, more than 71% of Iceland’s population had been vaccinated against COVID-19, which is comparable to only 26% of the study cohort of individuals with a history of COVID-19.
The results of the study indicate that reinfection with SARS-CoV-2 may be more common than originally expected. In the current setting, it is important to determine whether Omicron infection would result in enhanced immune protection against reinfection with Omicron compared to other SARS-CoV-2 VOCs.
Journal reference:
- Eythorsson , E. , Runolfsdottir , HL , Ingvarsson , RF , et al. (2022). SARS-CoV-2 reinfection rate during an Omicron wave in Iceland. JAMA Open Network 5(8). doi:10.1001/worldnetworks.2022.25320