Clinical Evaluation of the Accuracy of the Panbio™ COVID-19/Flu A&B Rapid Panel: A Combination Antigen Rapid Diagnostic Test for the Omicron Variant and Influenza A Virus

Abstract

It is difficult to differentiate between coronavirus disease 2019 (COVID-19) and influenza based on the symptoms. In the present study, a newly developed antigen rapid diagnostic test (Ag-RDT) called Panbio™ COVID-19/Flu A&B that can simultaneously detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A/B virus was evaluated. Its accuracy was evaluated using 235 pairs of nasopharyngeal samples collected from patients with respiratory symptoms and fever (>37.5°C). Reverse transcription polymerase chain reaction was used as a reference method to evaluate the accuracy of the SARS-CoV-2 detection. We confirmed the accuracy of the developed Ag-RDT against the Omicron variant where the sensitivity and specificity were 94.8% and 100%, respectively. In addition, to identify the influenza A virus, a noninferiority test was conducted using a commercial Ag-RDT, which has a sensitivity and specificity in comparison with viral culture of 94.8% and 98.4%, respectively. The positive and negative predictive values for influenza A virus were 98.5% and 98.1%, respectively, for the Panbio COVID-19/Flu A&B test. The evaluation of this newly developed Ag-RDT using clinical samples suggests that it has a high efficacy in clinical settings.

Introduction

Coronavirus disease 2019 (COVID-19) and influenza have identical clinical manifestations, including fever and respiratory tract symptoms. As a result, it is difficult to differentiate between these two conditions based solely on clinical symptoms (Centers for Disease Control and Prevention, 2024; Stowe et al., 2021).

These circumstances have prompted the development of antigen rapid diagnostic tests (Ag-RDTs) that can simultaneously detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus (Batty et al., 2023; Bayart et al., 2023; Dinç et al., 2023; Ellis et al., 2022; Fanshawe et al., 2024; Kang et al., 2024; Takeuchi et al., 2022; Widyasari et al., 2022). However, most of the reports are based on laboratory or residual samples, while few reports are based on clinical samples.

Panbio™ COVID-19/Flu A&B (Abbott Medical Japan LLC, Tokyo, Japan) is an Ag-RDT that can simultaneously detect SARS-CoV-2 and influenza A/B, which was approved in Europe in May 2022. This study was conducted in Japan to obtain marketing approval for Panbio COVID-19/Flu A&B. The accuracy of the Ag-RDT against the SARS-CoV-2 Omicron variant and influenza A/B was evaluated using clinical samples.

Materials and Methods

Patients

Patients with clinically suspected COVID-19 or influenza who visited Zama Children’s Clinic, Abe Children’s Clinic, or Jichi Children’s Medical Center, Tochigi, Japan, were enrolled. The study period was set based on the epidemic of the virus. The study period for SARS-CoV-2 was between September 1 and December 31, 2022. During this time, Japan experienced an outbreak of the Omicron variant (National Institute of Infectious Diseases, 2023). The study period for influenza was between January 1 and March 31, 2023; this period was chosen based on the duration of the influenza epidemic in Japan. The inclusion criteria were as follows: (1) patients with symptoms of fever (≥37.5°C); (2) those with respiratory symptoms such as cough, runny nose, nasal obstruction, and sore throat, headache, and fatigue; and (3) those in whom symptoms appeared within 8 days of onset. The exclusion criteria were as follows: patients with (1) hemorrhagic disorder and (2) nasal injury. According to the Declaration of Helsinki, all experiments involving human participants were performed. Written informed consent was obtained from all the participants. Written informed consent was obtained from the surrogate parent or guardian, if the participants were <18 years of age.

Sample collection

Two clinical specimens of nasopharyngeal swabs were collected simultaneously: one for evaluating the newly developed Ag-RDT and the other for reference evaluation. Samples were collected according to the Centers for Disease Control and Prevention’s (CDC) guidelines (Centers for Disease Control and Prevention, 2022): the swab was inserted into the nasopharyngeal site for 10 sec, and samples were collected after five rotations.

Evaluation of diagnostic accuracy of the Ag-RDT for COVID-19

To validate the diagnostic accuracy of SARS-CoV-2 using the clinical samples, reverse transcription polymerase chain reaction (RT-PCR) was performed as a reference method. One of the two clinical samples was tested using Panbio COVID-19/Flu A&B within 1 h of collection. The test procedure followed the manual attached to Panbio COVID-19/Flu A&B. We placed the swab sample into the buffer fluid inside the extraction buffer tube. Then, four drops of the extracted sample were placed vertically into the specimen well on the device, and the results were evaluated after 15–20 min. The presence of two lines, the test line COVID-19 and the control line, was assessed as positive, and the presence of only the control line as negative. The other samples were stored in 3 mL of Universal Transport Medium (Copan Italia S.p.A., Brescia, Italy) and frozen at −80°C for RT-PCR. Viral RNA for RT-PCR was extracted using the spin protocol of the QIAmp Viral RNA Mini Kit (QIAGEN, Hilden, Germany); 5 µL of the extracted RNA was used for RT-PCR of SARS-CoV-2, which was performed using Primer/Probe N2 (2019-nCov) (Takara Bio, Shiga, Japan) (Forward: 5′-AATTTTGGGGACCAGGAAC-3′, Reverse: 5′-TGGCAGCTGTGTAGGTCAAC-3′, and Probe: FAM-ATGTCGCGCATTGGCATGGA-BHQ) and One Step PrimeScript III RT-qPCR Mix with UNG (Takara Bio) according to the method described by the National Institute of Infectious Disease of Japan (Shirato et al., 2020). Samples whose amplification curve did not increase within 40 cycles were considered negative.

Mutation analysis of SARS-CoV-2

The Omicron variants were identified and distinguished using Primer/Probe E484A, T547K, and F486V (Shimadzu Corporation, Kyoto, Japan). The presence of E484A means the SARS-CoV-2 is an Omicron variant, and the presence of T547K means it is BA.1. The presence of F486V implies it is BA.4 or BA.5 but does not distinguish between BA.4 and BA.5 (Wilhelm et al., 2022). Furthermore, for samples without E484A, T547K, and F486V, it was impossible to determine the lineage of SARS-CoV-2. Therefore, whole-genome sequencing was performed for detailed lineage analysis. During the sample collection period, samples without E484A, T547K, and F486V and several samples with F486V collected every week were subjected to whole-genome sequencing of SARS-CoV-2 using Illumina COVID-seq with ARTC V4.1 primers and the Illumina NextSeq 2000 instrument (Illumina Inc., San Diego, CA, USA) for detailed mutation analysis of the Omicron variant (Lambisia et al., 2022).

Evaluation of diagnostic accuracy of the Ag-RDT for influenza A and B

To verify the diagnostic accuracy of the Panbio COVID-19/Flu A&B kit for influenza A or B, one sample was tested using the Panbio COVID-19/Flu A&B kit, whereas the other was tested using the QuickNavi™-Flu2 kit (Denka Co., Ltd., Tokyo, Japan), a commercially available Ag-RDT in Japan; for influenza A, it has a sensitivity of 94.8% and specificity of 98.4%; its sensitivity and specificity for influenza B are 97.8% and 96.8%, respectively (Ichikawa et al., 2013). To confirm the cycle threshold (Ct) values of the influenza virus, RT-PCR of the remaining buffer was performed if Ag-RDT results were conflicting. The QuantiTect Probe PCR Kit (Qiagen), TaqMan probe (5′-FAM-ATYTCGGCTTTGAGGGGGCCTG-MGB-3′), primers for influenza A (Forward: 5′-CCMAGGTCGAAACGTAYGTTCTCTCTATC-3′ and Reverse: 5′-TGACAGRATYGGTCTTGTCTTTAGCCAYTCCA-3′), and primers for influenza B (Forward: 5′-GGAGCAACCAATGCCAC-3′ and Reverse: 5′-GTKTAGGCGGTCTTGACCAG-3′) were used for RT-PCR based on the Influenza Diagnostic Manual of the National Institute of Infectious Diseases of Japan (National Institute of Infectious Diseases, 2023). Samples whose amplification curve did not increase within 40 cycles were considered negative.

Diagnostic accuracy of Ag-RDT for mixed clinical samples of SARS-CoV-2 and influenza

For SARS-CoV-2 and influenza A, we selected specimens of the Universal Transport Medium used for clinical samples with low and high Ct values, respectively: SARS-CoV-2, 25.8 (low Ct) and 28.4 (high Ct); Influenza A, 23.5 (low Ct) and 27.0 (high Ct). For each specimen of Universal Transport Medium, 50 µL was pipetted into a sterile tube and a swab was dipped into it. The swab was then dipped into the buffer attached to the Ag-RDT kit and was examined according to the instructions in the Panbio COVID-19/Flu A&B manual. We also mixed 50 µL each of the Universal Transport Medium specimens of (1) low-Ct SARS-CoV-2 and low-Ct influenza A; (2) high-Ct SARS-CoV-2 and high-Ct influenza A; (3) low-Ct SARS-CoV-2 and high-Ct influenza A; and (4) high-Ct SARS-CoV-2 and low-Ct influenza A. Swabs were dipped into each of these 100 µL mixtures (1–4) and then tested according to the instructions in the Panbio COVID-19/Flu A&B manual. The line appearing on the Ag-RDT kit was visually confirmed.

Statistical analysis

Statistical analyses were performed using R software version 4.1.0 (www.r-project.org) (R Foundation for Statistical Computing, Vienna, Austria). The sensitivity and specificity of the Ag-RDT were calculated using the Clopper–Pearson method, with 95% confidence intervals (95% CIs).

Ethics

This study was approved by the Research Ethics Review Committee of Jichi Medical University Hospital (approval no. 22-–028) and Ethics Committees of Zama Children’s Clinic and Abe Children’s Clinic, Eiju General Hospital, who provided blanket approval (approval no. 2022-13).

Results

A total of 175 patients participated in this study; the age range was 0–49 years (mean age, 11.8 years; median, 9 years). Two clinical specimens of nasopharyngeal swabs were collected simultaneously, one for evaluating the newly developed Ag-RDT and the other for reference evaluation.

To evaluate the diagnostic accuracy of the Ag-RDT for COVID-19, 135 pairs of samples were collected from 59 patients. Nine samples were collected on day 1, 32 on day 2, 18 on day 3, 22 on day 4, 19 on day 5, 15 on day 6, 14 on day 7, and 4 on day 8. Ag-RDT sensitivity and specificity were calculated relative to the RT-PCR results. Sensitivity was calculated by dividing the number of positives based on Ag-RDT by the number of positives based on RT-PCR. Specificity was calculated by dividing the number of negatives based on Ag-RDT by the number of negatives based on RT-PCR. Seventy-seven specimens were SARS-CoV-2-positive via RT-PCR. The mean Ct value was 21.0 (range: 12.1–37.9). Furthermore, the SARS-CoV-2 sensitivity was 94.8% (73/77 samples, 95% CI: 87.2–98.6%) and specificity was 100% (58/58 samples, 95% CI: 90.9–100%) (Tables 1 and 2). Two specimens collected on day 1 (<6 h after onset) and two specimens collected on day 8 after onset were considered false negatives. The range of the four false-negative samples was 25.9–37.9. Furthermore, the sensitivity on days 1 and 8 was 60.0% and 33.3%, respectively. The mean Ct values on days 1 and 8 were 28.3 (range: 21.9–37.9) and 26.6 (range: 23.1–30.8), respectively. The sensitivity on days 2–7 after onset was 100%, and the mean Ct value on days 2–7 was 20.2 (range: 12.1–29.5).

Table 1.

Accuracy of Panbio^™ COVID-19/Flu A&B Kit SARS-CoV-2-Detection Results Relative to RT-PCR Results

	Panbio COVID-19/Flu A&B
	Positive	Negative	Total
RT-PCR
Positive	73	4	77
Negative	0	58	58
Total	73	62	135
Sensitivity (95% CI)	94.8%	(87.2–98.6)
Specificity (95% CI)	100%	(90.9–100)

CI, confidence interval; RT-PCR, reverse transcription polymerase chain reaction; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Table 2.

Sensitivity of Panbio^™ COVID-19/Flu A&B Kit Based on SARS-CoV-2 Ct Values.

			Panbio COVID-19/Flu A&B
			Positive	Negative	Sensitivity (%)	95% CI (%)
RT-PCR	<20 Ct	(n = 32)	32	0	100	84.2–100
	20–30 Ct	(n = 42)	41	1	97.6	87.4–99.9
	30–40 Ct	(n = 3)	0	3	0	0–80.6

CI, confidence interval; Ct, cycle threshold; RT-PCR, reverse transcription polymerase chain reaction; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

All samples were positive for SARS-CoV-2 using RT-PCR harbored the E484A mutation. Furthermore, 72 samples harbored the F486V mutation. Whole-genome sequencing was performed on 16 of the 72 samples with F486V and 5 samples without F486V. All specimens with F486V were the BA.5 variant, whereas those without F486V were the BA.2 variant. Omicron BA.5 and BA.2 samples with a Ct value of <29.5 were accurately detected using Panbio COVID-19/Flu A&B, regardless of the variant.

Next, to evaluate the diagnostic agreement of influenza A and B viruses, 118 pairs of samples were collected from 116 patients. Thirty-four specimens were collected on day 1, 64 on day 2, 14 on day 3, 3 on day 4, 2 on day 5, and 1 on day 6 after onset. No specimens were collected on days 7 and 8. Sixty-six specimens were positive for influenza A virus using QuickNavi-Flu2; however, no cases of type B were detected. There were two samples for which the result of QuickNavi-Flu2 and Panbio COVID-19/Flu A&B did not match. One specimen (#1) that was collected on day 1 (<3 h after onset) was positive for influenza A virus using QuickNavi-Flu2 but negative using Panbio COVID-19/Flu A&B. In contrast, one specimen (#2) that was collected on day 2 after onset was negative for influenza A virus using QuickNavi-Flu2 but positive using Panbio COVID-19/Flu A&B. For influenza A virus, the positive predictive value was 98.5% (95% CI: 91.8–100%) and negative predictive value was 98.1% (95% CI: 89.7–100%) (Table 3). Specimen #1 had a Ct value of 25.9 using QuickNavi-Flu2 and 34.4 using Panbio COVID-19/Flu A&B; this suggests that the sensitivity of Panbio COVID-19/Flu A&B was not decreased; however, there may have been a technical problem during the collection of the two specimens. The #2 specimen had a Ct value of 37.8 using QuickNavi-Flu2 and 34.3 using Panbio COVID-19/Flu A&B. In other words, both specimens had a low viral load; nevertheless, Panbio COVID-19/Flu A&B could accurately assess samples with Ct values of ∼34.

Table 3.

Predictive Values Between QuickNavi^™-Flu2 and Panbio^™ COVID-19/Flu A&B for Influenza A Virus

	QuickNavi-Flu2
	Positive	Negative	Total
Panbio COVID-19/Flu A&B
Positive	65	1	66
Negative	1	51	52
Total	66	52	118
PPV (95% CI)	98.5%	(91.8–100)
NPV (95% CI)	98.1%	(89.7–100)

CI, confidence interval; NPV, negative predictive value; PPV, positive predictive value.

For the mixed specimens, both the COVID-19 and influenza A lines were detected. The lines did not differ visually from those obtained when the SARS-CoV-2 and influenza A samples were tested separately (Supplementary Fig. S1).

Discussion

Panbio COVID-19/Flu A&B exerts high sensitivity and specificity against the BA.2 laboratory Omicron variant (Batty et al., 2023). Despite the limited number of samples, this study revealed the high performance of Panbio COVID-19/Flu A&B against BA.2 and BA.5. The Ag-RDT test detects the nucleocapsid protein of SARS-CoV-2 as an antigen (Abbott, 2023). Whole-genome sequencing has revealed that the BA.2 and BA.5 viruses exhibit several amino acid mutations in the nucleocapsid protein. Nonetheless, BA.2 and BA.5 were accurately detected in all the samples (Supplementary Table S1). For influenza A, Panbio COVID-19/Flu A&B was noninferior to QuickNavi-Flu2. The World Health Organization (WHO) and CDC recommend that an Ag-RDT should be performed within 7 days of symptom appearance when COVID-19 is suspected and within 4 days of when influenza is suspected (Centers for Disease Control and Prevention, 2016; 2023; World Health Organization, 2022). In addition, WHO recommends that Ag-RDTs for SARS-CoV-2 detection should be evaluated using clinical samples from a novel mainstream variant of the epidemic, with a sensitivity of 80% and specificity of at least 97% (World Health Organization, 2021). Specimens collected on day 2 that were incompatible with QuickNavi-Flu2 were compatible with RT-PCR. Moreover, Panbio COVID-19/Flu A&B had 100% sensitivity and specificity for detecting SARS-CoV-2 and influenza A more than 6 h after onset and up to 7 days. Therefore, Panbio COVID-19/Flu A&B can be a useful Ag-RDT during the period recommended by the WHO.

Ag-RDTs are simple and useful diagnostic modalities. Furthermore, Ag-RDTs that can simultaneously detect multiple pathogens, such as Panbio COVID-19/Flu A&B, can reduce the distress of patients caused by the collection of multiple samples. Simultaneously, it can decrease the risk of pathogen exposure to health care professionals who collect the samples. Apart from Panbio COVID-19/Flu A&B, only Fluorecare^® (Microprofit Biotech Co., Ltd., Shenzhen, China) has been evaluated using the clinical samples of SARS-CoV-2 and influenza virus (Bayart et al., 2023). However, genetic analysis of SARS-CoV-2 was not performed; therefore, its exact efficacy against the currently prevalent Omicron variant remains unknown.

With the results of this study, Panbio COVID-19/Flu A&B was approved for manufacturing and marketing in Japan on June 27, 2023. We believe that this newly developed Ag-RDT will contribute to medical care by accurately diagnosing patients with COVID-19 and influenza with respiratory symptoms along with fever, leading to the early treatment of these conditions.

Footnotes

Acknowledgement

We appreciate Mr. Hiroyuki Nakayama, National Collaboration Development Group Government and Academic Collaboration Unit Sales & Marketing Division Shimadzu Corporation, for his technical support in mutation analysis.

Authors’ Contributions

H.Y.: Conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing—original draft, project administration, funding acquisition. D.T.: Conceptualization, methodology, software, validation, writing—reviewing and editing. M.Y. and T.A.: Data curation and writing—reviewing and editing. K.M.: Data curation, writing—reviewing and editing, and project administration. T.T.: Conceptualization and writing—reviewing and editing. H.O.: Conceptualization, writing—reviewing and editing, and supervision.

Author Disclosure Statement

The authors have no competing interests to declare.

Funding Information

This work was supported by Abbott Diagnostics Medical Co. Ltd. (funding and donation of product).

Supplementary Material

Supplementary Figure S1

Supplementary Table S1

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Supplementary Material

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