Evaluation of possible COVID-19 reinfection in children: A multicenter clinical study

Abstract

Background

Although it was originally unknown whether there would be cases of reinfection of coronavirus disease 2019 (COVID-19) as seen with other coronaviruses, cases of reinfection were reported from various regions recently. However, there is little information about reinfection in children.

Methods

In this study, we aimed to investigate the incidence and clinical findings of reinfection in pediatric patients who had recovered from COVID-19. We retrospectively evaluated all patients under 18 years of age with COVID-19 infection from a total of eight healthcare facilities in Turkey, between March 2020 and July 2021. Possible reinfection was defined as a record of confirmed COVID-19 infection based on positive reverse transcription-polymerase chain reaction (RT-PCR) test results at least 3 months apart.

Results

A possible reinfection was detected in 11 out of 8840 children, which yielded an incidence of 0.12%. The median duration between two episodes of COVID-19 was 196 (92–483) days. When initial and second episodes were compared, the rates of symptomatic and asymptomatic disease were similar for both, as was the severity of the disease (p = 1.000). Also, there was no significant difference in duration of symptoms (p = 0.498) or in hospitalization rates (p = 1.000). Only one patient died 15 days after PCR positivity, which resulted in a 9.1% mortality rate for cases of reinfection in pediatric patients.

Conclusion

We observed that children with COVID-19 were less likely to be exposed to reinfection when compared with adults. Although the clinical spectrum of reinfection was mostly similar to the first episode, we reported death of a healthy child during the reinfection.

1. Introduction

More than 490 million people have been affected by the COVID-19 pandemic and more than 6 million people have died worldwide to date [1]. The incidence of COVID-19 disease in children is dramatically lower than in adults. Since the beginning of the pandemic, 1–15% of COVID-19 cases reported from various countries are children [2], [3], [4], [5]. More than half of the pediatric patients have asymptomatic and mild disease, whereas critical disease has been reported in only 1% [6].

The mechanism of protective immunity, the level of protection, and the duration after infection with COVID-19 are still not known [7,8]. While it was originally unknown whether there would be reinfection in COVID-19 as seen with other coronaviruses, the first case of reinfection was of an adult patient and was reported from Hong Kong. Subsequently, cases of reinfection with COVID-19 from various regions have been recently reported [9], [10], [11]. All of the proven reinfections reported in the literature concern adults, and there is scarce information about reinfection in children. A weak humoral immune response or decreased antibody levels over time have been considered as causes of reinfection, while reinfection was shown to occur even in the presence of protective antibodies [7,12]. These issues can pose a challenge to the control of infection despite vaccination efforts, especially as new variants of COVID-19 have been defined that can evade the immune system [13].

In February 2020, the first variant was reported, which multiplied faster in the respiratory tract and was shown to be more contagious. It quickly became the dominant variant globally [14]. After that, the beta variant, which was more prone to escaping immunity, was identified. Subsequently, the delta variant was recognized, with an increased impact on the immune system causing greater disease severity and higher hospitalization rates [15]. The course of the pandemic depends on the effectiveness of immunity against COVID-19, its duration, the rate of vaccination, and herd immunity [16]. However, the increased incidence of reinfection has raised serious concerns about the control of this pandemic [17,18].

In this study, we aimed to investigate the incidence and clinical findings of reinfection in pediatric patients recovering from COVID-19.

2. Materials and methods

First, we retrospectively evaluated the data of 8840 patients under 18 years of age with COVID-19 infection from a total of eight healthcare facilities in Turkey, between March 2020 and July 2021. Patients who met the definition of possible reinfection were included in the study.

Demographic features and clinical findings of the patients such as the distribution and duration of symptoms, dates of the PCR test results, the cycle threshold (CT) values (if available), the severity of the disease, epidemiological contact information, follow-up results, and treatment outcomes were obtained from clinical records. Data of each episode of the infection were compared. None of the patients was vaccinated against COVID-19 since this study was performed before the onset of the vaccination for individuals under the age of 18 in our country.

The epidemiological case definition for COVID-19 reinfection was developed from a literature review on viral kinetics and data from the US Centers for Disease Control and Prevention (CDC) [11,[19], [20], [21], [22], [23]]. Possible reinfection was defined as a record of confirmed COVID-19 infections by positive RT-PCR test results at least 3 months apart. Between the two episodes of infection, all symptoms disappeared, laboratory and clinical findings were improved, and a negative COVID-19 PCR test result was observed (if performed) [24].

An RT-PCR test was performed using nasopharyngeal swabs. Multiple tests of a patient were matched using an individual laboratory identification number. The CT value was determined as the number of cycles of PCR amplification necessitated to find the gene target. Since a CT value is low in individuals with a high viral load, a high CT value is expected in persistent viral shedding. Therefore, a low CT value showed a high viral load and was used to differentiate reinfection [9]. In this study, a CT value for a specimen culture positivity was set at ≤32 [25,26]. The severity of COVID-19 disease was classified as asymptomatic, mild, moderate, severe, and critical according to the Infectious Diseases Society of America [27].

2.1. Ethics

This study was approved by the Ethics Committee of Dokuz Eylül University (Ethics approval number: 2021/20-27) and performed in accordance with the principles of the Declaration of Helsinki.

2.2. Statistical analysis

All statistical analyses were performed using the SPSS application for Windows version 24.0 (IBM Co., Armonk, NY, USA). Clinical data are presented as counts and percentages, or medians with the respective minimum–maximum values. Comparisons of paired categorical variables were performed using McNemar's test, while continuous variables were analyzed using the Wilcoxon sign rank test. The Spearman correlation test was applied for correlations between continuous variables. The odds ratio (OR) (with a 95% confidence interval [CI]) was calculated without any continuity correction to determine the rate of reinfection among those who recovered after an initial COVID-19 infection. A value of p<0.05 was considered statistically significant.

3. Results

Possible reinfection was detected in 11 out of 8840 children who tested positive for COVID-19, which corresponded to an incidence of 0.12% (95% CI: 0.05–0.19). The median age of those who were diagnosed with reinfection was 13.8 (0.7–17.8) years, eight (73%) of whom were female. Five (45%) of the patients had underlying comorbidity (Table 1 ). The median duration between two positive COVID-19 PCR test results was 196 (92–483) days.

Table 1.

Demographic features, clinical characteristics, and treatment outcomes of patients with COVID-19 infection and reinfection.

Clinical characteristics	Case 1	Case 2	Case 3	Case 4	Case 5	Case 6	Case 7	Case 8	Case 9	Case 10	Case 11
Age (years)	16.5	17	13	17	6	36 days	12.5	17	14.6	8.5	9
Gender	Male	Female	Female	Female	Male	Male	Female	Female	Male	Female	Male
Underlying disease	–	Cerebral palsy	Acute leukemia	Renal transplantation	Hemophilia A	Metabolic disease	–	–	Allergic rhinitis	–	PFAPA
First infection
Symptomatic	+	+	–	+	+	+	+	+	+	–	+
Duration of symptoms (days)	2	10	–	3	2	2	2	7	10	–	3
Epidemiological contact	Household	–	–	–	–	Household	Household	Others	Others	Household	Household
Severity of the disease	Mild	Severe	Asymptomatic	Moderate	Mild	Moderate	Mild	Mild	Mild	Asymptomatic	Mild
CT value	N/A	N/A	29.3	N/A	24.2	N/A	N/A	N/A	N/A	24.5	N/A
Follow-up	Outpatient	Hospitalized	Outpatient	Hospitalized	Hospitalized	Hospitalized	Outpatient	Outpatient	Outpatient	Outpatient	Outpatient
Treatment	–	Hydroxychloroquine	–	Favipiravir	Supportive	Supportive	–	–	–	–	–
Duration of treatment (days)	–	5	–	7	7	–	–	–	–	–	–
Reinfection
Duration between infections (days)	161	353	92	113	108	227	280	196	110	483	207
Symptomatic	+	+	+	–	–	+	+	+	+	+	+
Duration of symptoms (days)	15	5	6	–	–	2	2	2	2	3	2
Epidemiological contact	–	Household	–	–	–	–	–	Others	Household	Household	–
Severity of the disease	Critical	Severe	Mild	Asymptomatic	Asymptomatic	Moderate	Mild	Mild	Mild	Mild	Mild
CT value	N/A	N/A	30.5	N/A	33.0	N/A	N/A	N/A	N/A	20.1	N/A
Follow-up	Intensive care unit	Hospitalized	Hospitalized	Outpatient	Outpatient	Hospitalized	Outpatient	Outpatient	Outpatient	Outpatient	Outpatient
Treatment	Favipiravir	Supportive	Supportive	–	–	Supportive	–	–	–	–	–
Duration of treatment (days)	10	14	–	–	–	–	–	–	–	–	–
Death	+	–	–	–	–	–	–	–	–	–	–

CT: cycle threshold, N/A: not available, PFAPA: periodic fever, aphthous stomatitis, pharyngitis, adenitis syndrome.

In the first PCR positivity, nine (82%) of the patients were symptomatic. The most common symptoms were cough (55%) and fever (45%). The median duration of symptoms was 3 (2–10) days. Epidemiological contact was present in seven (%64) patients, five (45%) of which were household contacts. In the second PCR positivity, nine (82%) of the patients were symptomatic. The most common symptoms were fever (36%), headache (27%), and sore throat (27%). The mean duration of the symptoms was 2 (2–15) days. Epidemiological contact was present in four (36%) patients, three (27%) of which were household contacts (Table 1).

Two individuals, who were asymptomatic at the time of the first infection, had a mild disease during the second infection. The severity of the disease was similar in nine (81.8%) of the patients between the first and second episodes. During the reinfection, one patient (9.1%) had a milder disease and one patient (9.1%) had a more severe disease than the first episode. Only one (9.1%) patient died: a case associated with reinfection. A 16.5-year-old male patient (case 1) who had mild signs of upper respiratory tract infection at the initial infection was admitted to the clinic for acute encephalitis and pneumonia at the time of reinfection. The patient was followed up in the intensive care unit for 10 days and favipiravir and supportive treatments were administered (Table 1). However, he died 15 days after the PCR positivity, which resulted in a 9.1% mortality rate for reinfection in pediatric patients.

When initial and second episodes were compared, rates of symptomatic disease were similar in both, as was the severity of the disease (p = 1.000). Moreover, there was no significant difference in the duration of symptoms (p = 0.498) or in the hospitalization rates (p = 1.000). The time interval between the first and second episodes was similar in terms of the frequency of asymptomatic disease, the severity of disease, or hospitalization rates (p>0.05). Also, we could not find a correlation between the duration of symptoms and the time interval between infections (p = 0.893).

4. Discussion

Our study analyzed the incidence and clinical findings of reinfection in children by scanning a large population of pediatric patients with COVID-19 for a period of 16 months. Throughout our study period, different variants of COVID-19 were observed commonly around the world. The first variant was described in February 2020 and named alpha, which quickly became the predominant variant globally. Afterward, the beta and delta variants were identified in August and October 2020, respectively, and were thought to be the possible causes of COVID-19 infections during these periods [14].

As the pandemic continues, a question has arisen as to whether individuals who have recovered from COVID-19 will be reinfected. Early in the pandemic, it was believed that the second infection (reinfection) was merely a continuation of the first. However, in a 33-year-old man from Hong Kong, different viral genome sequences were reported in the first and second infections, 142 days apart [10]. Following this first case of reinfection, patients ranging in age from 15 to 99 years were described with reinfection [28], [29], [30], [31], [32]. After these reported cases, inquiries arose about its frequency, how long it took to occur, and whether the second infection was more severe or milder, with several studies focusing on this subject [29], [30], [31], [32], [33], [34].

Lumley et al. [35] reported a 0.11% incidence of COVID-19 infection in seropositive healthcare workers for anti-spike IgG antibodies. A study in London that included PCR and antibody test results from 66,001 patients documented eight patients with evidence of reinfection and calculated a 0.0578 relative risk of reinfection [30]. An observational study from Denmark reported that, among 11,068 individuals who had a positive PCR test during the first surge, 72 also tested positive at the second surge (0.65%) [30]. In another study, the reinfection rate was found to be 0.7% in a large cohort of cases [3]. Pilz et al. [29] demonstrated reinfection in 40 patients (0.27%) during the second wave among 15,424 patients with positive PCR tests during the first wave. Also, the probability of reinfection in adults was found to be similar to the risk of being infected with COVID-19 after vaccination [29]. Recently, a nationwide report from the United Kingdom showed the risk of possible reinfection in children under 16 years of age to be 0.34% [36]. In the present study, we found the frequency of possible reinfection in children to be 0.12% (95% CI: 0.05–0.19). Although this was a lower incidence than those reported, especially in adults, it may be explained by the fact that COVID-19 disease is less common in children than in adults.

Pilz et al. [29] found the mean time from the first to the second infection to be 212 days. In another study, a shorter time between two episodes was reported of 119 days [33]. We found the median duration between the two positive COVID-19 PCR test results to be 196 days in our study, similar to the previous reports. Also, the time interval between the first and second episodes did not affect the clinical course of reinfection. The European CDC stated that a longer time interval between two positive PCR results increased the likelihood of reinfection as it related to waning immunity and lower antibody levels [9,37]. Other authors have also recommended a time interval of 90 days to differentiate reinfection from relapse or re-positivity. However, when making epidemiological definitions, we should not ignore the fact that reinfection cases that occur less than 3 months apart will be missed.

Mukherjee et al. [33] reported that in a cohort of 38 adult patients with probable reinfection, 47.7% were asymptomatic during the primary infection and 15.8% were asymptomatic during the secondary infection. Our results showed an asymptomatic infection rate of 18% during both the first and second episodes. Mensah et al. [36] found that reinfections were more asymptomatic than the initial infection in pediatric cases. While COVID-19 is mostly asymptomatic in children, we found that most of the reinfected children were symptomatic at the initial infection. Symptomatic patients may be more susceptible to being reinfected than those without symptoms. While some studies showed that individuals reinfected with COVID-19 have milder symptoms than the initial infection, there are also reports of the opposite occurring [38,39]. One study showed that it can cause worse symptoms and serious complications, especially in older adults and immunocompromised individuals, in about 20% of patients reinfected with COVID-19 [40]. In this study, we did not find a statistically significant difference in the distribution of symptoms during the first and second episodes of infection. According to the previous reports of patients with SARS‐Cov‐2 reinfection, only two adults died: one woman aged about 80 years and hospitalized due to respiratory failure [32], and a 72‐year‐old woman with a history of rhabdomyolysis [29]. We did not find a statistically significant difference in disease severity between the initial infection and reinfection in this study. On the other hand, the death of a child out of such a small number of patients can be thought of as a serious outcome of reinfection. This made us consider that in addition to individual genetic susceptibility to SARS-CoV-2, the diverse immune responses against different variants may have an impact on the disease severity. When this patient was reinfected and died, the delta variant was dominant and the clinical course of this variant was more severe. Also, the reported incidence of hospitalization was higher in this variant than was observed in the others, which might be the reason for such a severe episode in our patient [14,15].

Therefore, all pediatric patients with reinfection should be followed up closely for possible severe outcomes, since novel variants can also cause different disease activities.

Although the protection against COVID-19 after recovering from this infection seems to be almost similar to the efficacy of vaccination, an exact comparison cannot be made due to differences in study designs and study populations [41,42]. While discussions about vaccinations for COVID-19 in the pediatric age group are proceeding today, there is not enough information about reinfection and post-vaccination protection in this population.

To our knowledge, this is one of the early studies to investigate the possible prevalence of COVID-19 reinfection in a large pediatric population, and data on this subject are lacking. In addition to this strength, our study also has some limitations, such as its retrospective nature and the small number of patients with reinfection. However, reinfection in COVID-19 is a recent and rare problem, and there only a limited number of studies were available. As another limitation, we could not perform molecular genetic testing for definitive evidence of reinfection with SARS-CoV-2 or a variant analysis. Also, the CT value can help to distinguish persistent viral shedding and reinfection according to some authors. Nevertheless, its reliability is still controversial and we could not access these data for most of our patients [43]. Although proven reinfection can be defined by phylogenetic analysis as two different variants containing more than 10 single-nucleotide variations, epidemiological definitions are needed because there are millions of COVID-19 cases around the world and it is not possible to store samples of all positive individuals under suitable conditions for such a long time [8,9,44]. Therefore, the same epidemiological criteria were used for all patients in our study, and all of them were confirmed by PCR tests at regular intervals, which was compatible with daily clinical practice. There is a need for more clinical and molecular studies with larger cohorts in this area to elucidate the exact mechanisms of reinfection.

5. Conclusion

We observed that children with COVID-19 were less likely to be exposed to reinfection compared with adults. Also, the clinical spectrum and severity of reinfection were mostly similar to those in the first episode of this disease. However, we reported the death of a healthy child during reinfection, which can be considered a serious outcome. Although reinfection in COVID-19 has been a rare clinical entity to date, it may increase the challenges of controlling the pandemic, as novel variants continue to emerge and escape from the immune system remains an issue despite vaccination efforts.

Declaration of Competing Interest

None.