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Severity of SARS-CoV-2 reinfection compared to primary infection




To the editor:

In Qatar, there was the first wave of infection with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) from March to June 2020, after which about 40% of the population was detected for SARS-CoV-2. Had a possible antibody. Then there were two consecutive waves in the country from January to May 2021, triggered by the introduction of the B.1.1.7 (or alpha) and B.1.351 (or beta) variants.1 This created an epidemiological opportunity to assess reinfection.

Use a national federated database that collects all SARS-CoV-2 related data since the outbreak of the pandemic ( Supplementary appendix,, available with the full text of this letter), investigated the risk of severe illness (leading to acute hospitalization), serious illness (leading to hospitalization in the intensive care unit). [ICU]), And a fatal disease caused by reinfection compared to the primary infection in the national cohort of polymerase chain reaction (PCR)-confirmed infection between February 28, 2020 and April 28, 2021. Record of vaccination. The primary infection was defined as the first PCR-positive swab. Reinfection was defined as the first PCR-positive swab obtained at least 90 days after the primary infection. Reinfected individuals were consistent with primary infected individuals in a 1: 5 ratio depending on gender, age group of 5 years, nationality, and calendar week of PCR test date (Figure S1 and Table S1). Supplementary appendix). The severe, serious, and fatal Covid-19 classifications were evaluated by trained healthcare professionals through individual medical record reviews in accordance with World Health Organization guidelines.

Severity of SARS-CoV-2 reinfection compared to primary infection in Qatar’s population.

Of the 1304 reinfections identified, 413 (31.7%) were B.1.351 variants, 57 (4.4%) were B.1.1.7 variants, 213 (16.3%) were “wild-type” viruses, and 621 (47.6). Was the cause. %) The status was unknown (Section S1) Supplementary appendix). For reinfected individuals, the median time from initial infection to reinfection was 277 days (interquartile range, 179-315).The odds of serious illness at the time of reinfection were 0.12 times (95% confidence interval). [CI], 0.03 ~ 0.31) At the time of primary infection (table 1). When the odds ratio was 0.00 (95% CI, 0.00-0.64), there were no cases of serious illness at the time of reinfection and 28 cases at the time of primary infection (Table S3). There were no deaths from Covid-19 during reinfection, 7 deaths during primary infection, and an odds ratio of 0.00 (95% CI, 0.00-2.57). The odds of a combined outcome of serious, serious, or fatal disease at reinfection were 0.10 times (95% CI, 0.03 to 0.25) at primary infection. Sensitivity analysis was consistent with these results (Table S2).

Reinfection was 90% less likely to lead to hospitalization or death than primary infection. The four reinfections were severe enough to lead to acute hospitalization. None of them led to hospitalization in the ICU and none died. Reinfection was rare and was generally mild, probably due to the primed immune system after the primary infection.

Previous studies evaluated the effectiveness of previous natural infections as a defense against reinfection with SARS-CoV-2.2,3 Assuming that it is 85% or more. Therefore, for those who are already primary infected, the risk of severe reinfection is only about 1% of the risk of severe primary infection for those who have not been previously infected. As with the immunity that occurs against other seasonal “cold” coronaviruses, it is necessary to determine whether such protection against serious illness during reinfection lasts longer.Four It induces short-term immunity to mild reinfection, but it induces long-term immunity to more serious illnesses with reinfection. If this is the case for SARS-CoV-2, the virus (or at least the variants studied so far) may adopt a better infection pattern when it becomes endemic.Four

Dr. Rice J. Abu Raddad
Hiam Chemitery, Master
Weill Cornell Medicine – Qatar, Doha, Qatar

Roberto Bertorini, MD, MPH
Ministry of Public Health, Doha, Qatar

COVID-19 For the National Study Group for Epidemiology

Supported by the Biomedical Research Program and the Core of Biostatistics, Epidemiology, and Biological Mathematics Research. Weill Cornell Medicine – QatarNS Ministry of Public HealthHamad Medical Corporation; and Sidra Medicine. The Qatar Genome Program supported viral genome sequencing.

Disclosure form The one provided by the author is available on with the full text of this letter.

This letter was published on on November 24, 2021.

Members of the National Research Group for COVID-19 Epidemiology are listed in Supplementary appendixAvailable at with the full text of this letter.

  1. 1.1. Abu Raddad LJ, Chemaitelly H, Bat AA.. Efficacy of BNT162b2Covid-19 vaccine against B.1.1.7 and B.1.351 mutants. N Engl J Med 2021385:187――――189..

  2. 2.2. Abu Raddad LJ, Chemaitelly H, Coil P,other. SARS-CoV-2 antibody positivity is 95% effective and prevents reinfection for at least 7 months. EClinicalMedicine 202135:100861――――100861..

  3. 3.3. Abu Raddad LJ, Chemaitelly H, Marek JA,other. Assessment of the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection in a severe re-exposure environment.Clinical infections 202173 (7):e1830――――And 1840..

  4. 4.4. Ravine JS, Bjorn stud ON, Antia R.. Immunological characteristics govern the transition of COVID-19 to the epidemic.Chemistry 2021371:741――――745..

Severity of SARS-CoV-2 reinfection compared to primary infection in Qatar’s population.

The result of the illness*ReinfectionPrimary infectionOdds ratio (95% CI)
number. / No for those with results.Of people with severe, serious, or non-fatal infections
Severe illness4/1300158/60950.12 (0.03–0.31)
Serious illness0/130028/60950.00 (0.00–0.64)
Incurable disease0/13007/60950.00 (0.00–2.57)
Severe, severe, or fatal illness4/1300193/60950.10 (0.03–0.25)




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