[Skip to Navigation]
Sign In
Figure.  Proportion of Persons Reinfected With SARS-CoV-2 During the Omicron Wave of Infections in Iceland by Age Group, Vaccine Status, and Time From Initial Infection
Proportion of Persons Reinfected With SARS-CoV-2 During the Omicron Wave of Infections in Iceland by Age Group, Vaccine Status, and Time From Initial Infection

Shaded areas denote 95% CIs. A vertical dashed black line is drawn at 60 days. Persons whose initial infection occurred after that time were not at risk for reinfection on December 1, 2021, and were not included.

Table.  Number and Proportion of Persons Reinfected With SARS-CoV-2 During the Omicron Wave of Infections in Iceland, December 1, 2021, to February 13, 2022
Number and Proportion of Persons Reinfected With SARS-CoV-2 During the Omicron Wave of Infections in Iceland, December 1, 2021, to February 13, 2022
1.
Eggink  D, Andeweg  SP, Vennema  H,  et al.  Increased risk of infection with SARS-CoV-2 Omicron BA.1 compared with Delta in vaccinated and previously infected individuals, the Netherlands, 22 November 2021 to 19 January 2022.   Euro Surveill. 2022;27(4):2101196. doi:10.2807/1560-7917.ES.2022.27.4.2101196PubMedGoogle ScholarCrossref
2.
Pulliam  JRC, van Schalkwyk  C, Govender  N,  et al.  Increased risk of SARS-CoV-2 reinfection associated with emergence of Omicron in South Africa.   Science. 2022;376(6593):eabn4947. doi:10.1126/science.abn4947PubMedGoogle ScholarCrossref
3.
Altarawneh  HN, Chemaitelly  H, Hasan  MR,  et al.  Protection against the Omicron variant from previous SARS-CoV-2 infection.   N Engl J Med. 2022;386(13):1288-1290. doi:10.1056/NEJMc2200133PubMedGoogle ScholarCrossref
4.
Harrell  FE  Jr.  Regression Modeling Strategies. 2nd ed. Springer International Publishing; 2016.
5.
Iceland Directorate of Health. COVID-19 vaccinations in Iceland: statistics. 2022. Accessed March 11, 2022. https://www.covid.is/statistical-information-on-vaccination
Limit 200 characters
Limit 25 characters
Conflicts of Interest Disclosure

Identify all potential conflicts of interest that might be relevant to your comment.

Conflicts of interest comprise financial interests, activities, and relationships within the past 3 years including but not limited to employment, affiliation, grants or funding, consultancies, honoraria or payment, speaker's bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued.

Err on the side of full disclosure.

If you have no conflicts of interest, check "No potential conflicts of interest" in the box below. The information will be posted with your response.

Not all submitted comments are published. Please see our commenting policy for details.

Limit 140 characters
Limit 3600 characters or approximately 600 words
    1 Comment for this article
    EXPAND ALL
    Reanalysis and improvement suggestions
    Matthew Elvey, Computer Science, MechEng | Yale University
    A supplementary analysis without having grouped together zero and one vaccine doses and two or more doses would be informative. As many persons aged < 75 years had not received a single vaccine dose, and many persons aged > 29 years had received three or more doses, this reanalysis is warranted. (Also, a modifier is missing in "Because so few individuals had received a booster shot by December 1, 2021 had become reinfected, we dichotomized vaccine status to ≤1 dose and ≥2 doses." (such as 'who' or 'and...then') In the reanalysis, the rarity of those reinfections would be visible, rather than hidden, and usable in future meta-analyses.

    Additionally, in the code, the vacc_status case statement is problematic. The date logic is confused. There is code repetition/lack of code reuse/refactoring. Contrary to the "Rule of Three" (of Martin Fowler), the entire code is repeated with small changes 6 times in a row. (https://wou.edu/las/cs/csclasses/cs161/Lectures/rulesofthumb.html, https://www.infoq.com/news/2014/01/fowler-workflows-refactoring/) It seems so much longer than necessary that it is, in effect, obfuscated.

    If I'm not mistaken, swapping in this for the much longer original code section would enable the supplementary analysis:

    mutate(vacc_status = factor(case_when(
    !is.na(date_4) & date_4 <= as.Date("2021-11-17") ~ "4 vaccine doses",
    !is.na(date_3) & date_3 <= as.Date("2021-11-17") ~ "3 vaccine doses",
    !is.na(date_2) & date_2 <= as.Date("2021-11-17") ~ "2 vaccine doses",
    !is.na(date_1) & date_1 <= as.Date("2021-11-17") ~ "One dose",
    TRUE ~ "Unvaccinated"
    ), levels = c("4 vaccine doses", "3 vaccine doses", "2 vaccine doses", "One dose", "Unvaccinated")
    ))

    Furthermore, if I'm not mistaken, swapping in this for the much longer original code section can be expected to result in the same output as the original, but is shorter and more readable:

    mutate(vacc_status = factor(case_when(
    !is.na(date_2) & date_2 <= as.Date("2021-12-01") ~ "Two or more vaccine doses",
    TRUE ~ "One dose or unvaccinated"
    ), levels = c("One dose or unvaccinated", "Two or more vaccine doses")
    )) %>%
    select(-date_4, -date_3, -date_2, -date_1, -name_4, -name_3, -name_2, -name_1)
    CONFLICT OF INTEREST: None Reported
    READ MORE
    Views 137,484
    Citations 0
    Research Letter
    Infectious Diseases
    August 3, 2022

    Rate of SARS-CoV-2 Reinfection During an Omicron Wave in Iceland

    Author Affiliations
    • 1Landspitali–The National University Hospital of Iceland, Reykjavik, Iceland
    • 2Faculty of Medicine, School of Health Sciences, University of Iceland, Reykjavik, Iceland
    JAMA Netw Open. 2022;5(8):e2225320. doi:10.1001/jamanetworkopen.2022.25320
    Introduction

    COVID-19 caused by SARS-CoV-2 was declared a global pandemic on March 11, 2020. Omicron, the currently dominant variant, is characterized by increased immune evasion, making reinfections more common.1,2 The relative protection of prior infection against reinfection with Omicron is 56% compared with 92% for the Delta variant.3 However, the population-level risk of reinfection with Omicron has not been described. The aim of this study was to estimate the proportion of persons who become reinfected with SARS-CoV-2 during the Omicron wave in Iceland.

    Methods

    The study was approved by the National Bioethics Committee of Iceland, which waived the need for informed consent. The study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline. This population-based cohort study monitored all persons previously infected with SARS-CoV-2 for reinfection during the Omicron wave in Iceland, which was defined from December 1, 2021 (first diagnosed case of Omicron in Iceland) to the end of the study period on February 13, 2022. Data on all SARS-CoV-2 polymerase chain reaction (PCR) test results performed in the country were obtained from Landspitali–The National University Hospital of Iceland, and data on vaccine status were obtained from the Icelandic Directorate of Health. Reinfection was defined as a positive PCR test for SARS-CoV-2 60 or more days from a previous positive test. The proportion reinfected by age group, vaccine status, and the number of elapsed days from the initial positive PCR test was estimated using logistic regression. Statistical analyses were performed in R statistical software version 4.1.2 (R Project for Statistical Computing) using the rms package.4 Detailed definitions and all statistical codes are provided in eAppendix 1 and eAppendix 2 in the Supplement.

    Results

    In total, 11 536 PCR-positive persons were included. The mean (SD) age was 34 (19) years (median, 31 years; range, 0-102 years), 5888 (51%) were male, 2942 (25.5%) had received at least 1 dose of vaccine, and the mean (SD) time from initial infection was 287 (191) days (median, 227 days; range, 60-642 days). Reinfection was observed in 1327 persons (11.5%) during the Omicron period. Of those who had received 1 dose or less of vaccine, 11.7% (1007 of 8598 individuals) were reinfected, compared with 10.9% (320 of 2938 individuals) who had received 2 or more doses. The reinfection rate was highest (475 of 3136 individuals [15.1%]) among those aged 18 to 29 years. Fewer reinfections occurred among older individuals (Table).

    The probability of reinfection increased with time from the initial infection (odds ratio of 18 months vs 3 months, 1.56; 95% CI, 1.18-2.08) (Figure) and was higher among persons who had received 2 or more doses compared with 1 dose or less of vaccine (odds ratio, 1.42; 95% CI, 1.13-1.78). Defining reinfection after 30 or more days or 90 or more days did not qualitatively change the results.

    Discussion

    In this population-based cohort study, a substantial proportion of persons experienced SARS-CoV-2 reinfection during the first 74 days of the Omicron wave in Iceland, with rates as high 15.1% among those aged 18 to 29 years. Longer time from initial infection was associated with a higher probability of reinfection, although the difference was smaller than expected. Surprisingly, 2 or more doses of vaccine were associated with a slightly higher probability of reinfection compared with 1 dose or less. This finding should be interpreted with caution because of limitations of our study, which include the inability to adjust for the complex relationships among prior infection, vaccine eligibility, and underlying conditions. Importantly, by December 1, 2021, all persons aged 12 years and older were eligible for 2 or more vaccine doses free of charge, and 71.1% of the Icelandic population had been vaccinated,5 compared with only 25.5% of our cohort of previously infected persons. Our results suggest that reinfection is more common than previously thought. Now the key question is whether infection with the Omicron variant will produce better protection against Omicron reinfection, compared with other variants.

    Back to top
    Article Information

    Accepted for Publication: June 19, 2022.

    Published: August 3, 2022. doi:10.1001/jamanetworkopen.2022.25320

    Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2022 Eythorsson E et al. JAMA Network Open.

    Corresponding Authors: Elias Eythorsson, MD, PhD, Landspitali–The National University Hospital of Iceland, Skaftahlid 24, 105 Reykjavik, Iceland (elias.eythorsson@gmail.com); Runolfur Palsson, MD, Landspitali–The National University Hospital of Iceland, Skaftahlid 24, 105 Reykjavik, Iceland (runolfur@landspitali.is).

    Author Contributions: Drs Eythorsson and Palsson had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

    Concept and design: Eythorsson, Sigurdsson, Palsson.

    Acquisition, analysis, or interpretation of data: All authors.

    Drafting of the manuscript: Eythorsson, Sigurdsson.

    Critical revision of the manuscript for important intellectual content: All authors.

    Statistical analysis: Eythorsson.

    Obtained funding: Eythorsson, Palsson.

    Administrative, technical, or material support: Ingvarsson, Sigurdsson, Palsson.

    Supervision: Sigurdsson, Palsson.

    Conflict of Interest Disclosures: None reported.

    Funding/Support: This work was supported by the Landspitali University Hospital Research Fund (grant A-2021-051). Neither the authors nor their institutions received payment or services from a third party for any aspect of the submitted work.

    Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

    References
    1.
    Eggink  D, Andeweg  SP, Vennema  H,  et al.  Increased risk of infection with SARS-CoV-2 Omicron BA.1 compared with Delta in vaccinated and previously infected individuals, the Netherlands, 22 November 2021 to 19 January 2022.   Euro Surveill. 2022;27(4):2101196. doi:10.2807/1560-7917.ES.2022.27.4.2101196PubMedGoogle ScholarCrossref
    2.
    Pulliam  JRC, van Schalkwyk  C, Govender  N,  et al.  Increased risk of SARS-CoV-2 reinfection associated with emergence of Omicron in South Africa.   Science. 2022;376(6593):eabn4947. doi:10.1126/science.abn4947PubMedGoogle ScholarCrossref
    3.
    Altarawneh  HN, Chemaitelly  H, Hasan  MR,  et al.  Protection against the Omicron variant from previous SARS-CoV-2 infection.   N Engl J Med. 2022;386(13):1288-1290. doi:10.1056/NEJMc2200133PubMedGoogle ScholarCrossref
    4.
    Harrell  FE  Jr.  Regression Modeling Strategies. 2nd ed. Springer International Publishing; 2016.
    5.
    Iceland Directorate of Health. COVID-19 vaccinations in Iceland: statistics. 2022. Accessed March 11, 2022. https://www.covid.is/statistical-information-on-vaccination
    ×