Frequency and risk of SARS-CoV-2 reinfections in Norway: a nation-wide study, February 2020 to January 2022

BACKGROUND

SARS-CoV-2 reinfection rates have been shown to vary depending on the circulating variant, vaccination status and background immunity, as well as the time interval used to identify reinfections. This study describes the frequency of SARS-CoV-2 reinfections in Norway using different time intervals and assesses potential factors that could impact the risk of reinfections during the different variant waves.

METHODS

We used linked individual-level data from national registries to conduct a retrospective cohort study including all cases with a positive test for SARS-CoV-2 from February 2020 to January 2022. Time intervals of 30, 60, 90 or 180 days between positive tests were used to define potential reinfections. A multivariable Cox regression model was used to assess the risk of reinfection in terms of variants adjusting for vaccination status, demographic factors, and underlying comorbidities.

RESULTS

The reinfection rate varied between 0.2%, 0.6% and 5.9% during the Alpha, Delta and early Omicron waves, respectively. In the multivariable model, younger age groups were associated with a higher risk of reinfection compared to older age groups, whereas vaccination was associated with protection against reinfection. Moreover, the risk of reinfection followed a pattern similar to risk of first infection. Individuals infected early in the pandemic had higher risk of reinfection than individuals infected in more recent waves.

CONCLUSIONS

Reinfections increased markedly during the Omicron wave. Younger individuals, and primary infections during earlier waves were associated with an increased reinfection risk compared to primary infections during more recent waves, whereas vaccination was a protective factor. Our results highlight the importance of age and post infection waning immunity and are relevant when evaluating vaccination polices.

SARS-CoV-2 reinfections: Overview of efficacy and duration of natural and hybrid immunity

Seroprevalence surveys suggest that more than a third and possibly more than half of the global population has been infected with SARS-CoV-2 by early 2022. As large numbers of people continue to be infected, the efficacy and duration of natural immunity in terms of protection against SARS-CoV-2 reinfections and severe disease is of crucial significance for the future. This narrative review provides an overview on epidemiological studies addressing this issue. National surveys covering 2020-2021 documented that a previous SARS-CoV-2 infection is associated with a significantly reduced risk of reinfections with efficacy lasting for at least one year and only relatively moderate waning immunity. Importantly, natural immunity showed roughly similar effect sizes regarding protection against reinfection across different SARS-CoV-2 variants, with the exception of the Omicron variant for which data are just emerging before final conclusions can be drawn. Risk of hospitalizations and deaths was also reduced in SARS-CoV-2 reinfections versus primary infections. Observational studies indicate that natural immunity may offer equal or greater protection against SARS-CoV-2 infections compared to individuals receiving two doses of an mRNA vaccine, but data are not fully consistent. The combination of a previous SARS-CoV-2 infection and a respective vaccination, termed hybrid immunity, seems to confer the greatest protection against SARS-CoV-2 infections, but several knowledge gaps remain regarding this issue. Natural immunity should be considered for public health policy regarding SARS-CoV-2.

Reinfection by the SARS-CoV-2 Gamma variant in blood donors in Manaus, Brazil

BACKGROUND

The city of Manaus, north Brazil, was stricken by a second epidemic wave of SARS-CoV-2 despite high seroprevalence estimates, coinciding with the emergence of the Gamma (P.1) variant. Reinfections were postulated as a partial explanation for the second surge. However, accurate calculation of reinfection rates is difficult when stringent criteria as two time-separated RT-PCR tests and/or genome sequencing are required. To estimate the proportion of reinfections caused by Gamma during the second wave in Manaus and the protection conferred by previous infection, we identified anti-SARS-CoV-2 antibody boosting in repeat blood donors as a mean to infer reinfection.

METHODS

We tested serial blood samples from unvaccinated repeat blood donors in Manaus for the presence of anti-SARS-CoV-2 IgG antibodies using two assays that display waning in early convalescence, enabling the detection of reinfection-induced boosting. Donors were required to have three or more donations, being at least one during each epidemic wave. We propose a strict serological definition of reinfection (reactivity boosting following waning like a V-shaped curve in both assays or three spaced boostings), probable (two separate boosting events) and possible (reinfection detected by only one assay) reinfections. The serial samples were used to divide donors into six groups defined based on the inferred sequence of infection and reinfection with non-Gamma and Gamma variants.

RESULTS

From 3655 repeat blood donors, 238 met all inclusion criteria, and 223 had enough residual sample volume to perform both serological assays. We found 13.6% (95% CI 7.0-24.5%) of all presumed Gamma infections that were observed in 2021 were reinfections. If we also include cases of probable or possible reinfections, these percentages increase respectively to 22.7% (95% CI 14.3-34.2%) and 39.3% (95% CI 29.5-50.0%). Previous infection conferred a protection against reinfection of 85.3% (95% CI 71.3-92.7%), decreasing to respectively 72.5% (95% CI 54.7-83.6%) and 39.5% (95% CI 14.1-57.8%) if probable and possible reinfections are included.

CONCLUSIONS

Reinfection by Gamma is common and may play a significant role in epidemics where Gamma is prevalent, highlighting the continued threat variants of concern pose even to settings previously hit by substantial epidemics.

Third wave of COVID-19 in Madrid, Spain

A third wave of COVID-19 occurred after Christmas 2020 in Madrid, one of the European pandemic epicenters. We noticed 6 major differential features to previous waves. First, household contacts were a large proportion of cases. Second, access to rapid antigen tests allowed prompt diagnosis and isolation. Third, clinically severe cases and mortality rates were lower. Fourth, the more transmissible B.1.1.7 strain was increasingly found. Fifth, vaccination benefits were seen in healthcare workers and nursing homes. Lastly, reinfections were more common. By Easter 2021, approximately 25% of the population in Madrid had been infected with SARS-CoV-2. Therefore, massive and accelerated vaccination campaigns are warranted to prevent new COVID-19 waves.

Are people with uncontrolled diabetes mellitus at high risk of reinfections with COVID-19?

Several cases of positive real time-polymerase chain reaction (RT-PCR) results (called "re-positives") after recovery from COVID-19 have emerged worldwide. These cases could represent patients experiencing a "turn positive" of nucleic acid detection attributed to the high false-negative rate of RT-PCR. On the contrary, in symptomatic patients, the possibility of reactivation or true reinfection remains. We hypothesize that people with uncontrolled diabetes mellitus might be at a high risk of reinfections with COVID-19 attributed to the impaired adaptive immune response. In fact, multiple cases of re-positives/re-infections in people with diabetes mellitus have hitherto been reported.

High rates of early HCV reinfection after DAA treatment in people with recent drug use attended at mobile harm reduction units

BACKGROUND AND AIMS

The World Health Organization recently called for the elimination of hepatitis C virus (HCV) and has identified people who inject drugs (PWID) as a key target population. Clinical trials analyzing currently available all-oral regimens have demonstrated a high degree of efficacy in this population, with a relatively low reinfection rate. There is an urgent need to confirm these data in a harm reduction and active consumption setting. The primary aim of this study was to evaluate the HCV reinfection rate in people with recent drug use followed at low-threshold mobile harm reduction units.

METHOD

We included people with recent drug use (smoked or injected heroin/cocaine in the previous 6 months) who received HCV treatment and were attended at two low-threshold mobile harm reduction units over 19 months. Sustained virologic response was assessed 12 weeks after therapy (SVR12). The incidence density of HCV reinfection was defined as the number of reinfections per 100-person years (PY) using person-time of observation and was stratified by drug consumption at initiation of HCV treatment. Cox proportional hazard regression analysis was used to assess factors associated with reinfection.

RESULTS

During the study period, 160 people who used drugs in the past 6 months completed HCV therapy. 122 (73.9%) and 88 (53.3%) reported injecting drug use in the 6 months and 30 days prior to HCV treatment, respectively. The overall SVR12 was 68% in the ITT analysis (reinfection = failure) and 90.7% in the modified intent-to-treat analysis (considering reinfections as response and removing people who were missing SVR data). The cohort at-risk for reinfection (n = 121) included 47 (39.2%) people who initiated HCV treatment with recently reported abstinence. Reinfection was identified in 10 persons (8.3%), and the median time to reinfection was 7.2 (IQR 4.2-18) months. Total follow-up time at-risk was 101.1-PY (median 0.6 years, IQR 0.3-1.3). The overall incidence of reinfection was 9.8 per 100-PY (95% CI 4.7,18.2). The incidence of reinfection was higher amongst those who had injected drugs in the previous 6 months (16.7 [95%CI 8.0; 30.7] per 100-PY) and in the previous 30 days (18.9 [95% CI 8.1; 37.2] per 100-PY). In the adjusted analysis, only injecting drugs use in the month prior to initiation of HCV therapy was associated with reinfection (aHR 8.7, 95%CI 1.0; 73.6; p 0.04).

CONCLUSION

High efficacy of HCV treatment, was found in people with recent drug use attended and followed at low-threshold mobile harm reduction units. The high rate of early HCV reinfections in this setting should promote surveillance for reinfection at 7-month intervals after ending the treatment or earlier.

Switch to oral antibiotics in the treatment of infective endocarditis is not associated with increased risk of mortality in non-severely ill patients

Although many international guidelines exist for the management of infective endocarditis (IE), recommendations are lacking on the opportunity of switching antibiotics from the intravenous (IV) to oral route during treatment. We present a cohort study of 426 cases of IE over a period of 13 years (2000-2012), including 369 cases of definite IE according to the Duke criteria. Predictors of mortality were identified using the Cox proportional hazard analysis. The median (range) age at diagnosis was 64.5 (7-98) years. One hundred six patients (25%) had healthcare-associated IE. Oral streptococci (n = 99, 23%) and Staphylococcus aureus (n = 81, 19%) were the predominant microorganisms. Ninety-two patients (22%) died during follow-up. After an initial phase of IV antibiotherapy, 214 patients (50%) were switched to oral route a median (range) of 21 (0-70) days after diagnosis of IE. Patients in the oral group had fewer comorbidities, and criteria of severity at inclusion and were less frequently infected by S. aureus. Oral antibiotics were amoxicillin alone in 109 cases or a combination therapy of clindamycin, fluoroquinolone, rifampicin and/or amoxicillin in 46 cases, according to the susceptibility of the microorganisms. In the multivariate analysis, a switch to oral route was not associated with an increased risk of mortality. During follow-up, only two relapses and four reinfections were observed in the oral group (compared to nine and eight in the IV group, respectively). In this study, switching to oral administration was not associated with an increased risk of relapse or reinfection. These promising results need to be confirmed by prospective studies.