The Loss of Respiratory Syncytial Virus Seasonality and the Effects on Palivizumab Administration.

Abstract

To the Editors: Palivizumab is a monoclonal antibody utilized in at-risk groups to provide passive protection against respiratory syncytial virus (RSV).1 Close matching with the local RSV season is required to optimize protection and minimize costs. In 2020, a significant disruption in seasonality was linked to severe acute respiratory syndrome coronavirus 2–associated nonpharmaceutical interventions.2 In Western Australia, an absent winter season was followed by a summer surge of RSV. This summer season was shorter but more intense than previous winter seasons, with a peak in admissions more than 2.5 times than observed previously.1 We conducted a retrospective review of the effects of the loss of RSV seasonality on palivizumab administration. We compared the timeliness of administration in all infants who received palivizumab during the 2019 and 2020/2021 RSV seasons at a single tertiary pediatric center in Western Australia. The season onset and offset threshold was set at 1.2% of total RSV detections per year.3 Date of first eligibility was ascertained from the latest time point of RSV season onset, diagnosis of a high-risk condition, or hospital discharge. The total number of eligible and received doses and the proportion of RSV season covered were also assessed. A total of 58 patients received palivizumab over the 2 seasons (Table 1). The 2019 season duration was 28 weeks (onset week 14 and offset week 41). The duration of 2020/2021 summer season was 14 weeks (onset week 45, 2020, offset week 5, 2021). The first palivizumab dose had a median time to initiation of 0 weeks in 2019, compared with 6.3 weeks in 2020/2021. In the 2019 season, 59% of eligible weeks were covered by palivizumab, weighed against 31% in the 2020/2021 season. There were no RSV-related admissions in 2020/2021 in this cohort and two in 2019. Of these admissions, one occurred between RSV seasons and the second occurred during the 2019 RSV season prior to the patient’s first palivizumab dose. TABLE 1. - Comparison of 2019 and 2020/2021 Season Outcomes 2019, n (%) 2020/2021, n (%) P Value Season duration (weeks) 28 14 Total 27 26 Median age, weeks (IQR) 9.86 (6.7–14.6) 24.8 (13.4–33.6) 0.004 Inpatient administration, n (%) 21 (75) 9 (35) 0.004 Clinical team Neonatology 9 (34) 5 (19) 0.3 Cardiology 10 (37) 10 (38) 0.9 Respiratory 1 (4) 6 (23) 0.03 Other 7 (26) 5 (19) 0.6 Eligible doses 1 7 (26) 7 (27) 2 1 (4) 1 (15) 3 5 (19) 18 (69) 4 6 (22) - 5 8 (30) - Doses administered 1 12 (44) 26 (100) 2 7 (26) - 3 3 (11) - 4 2 (7) - 5 3 (11) - Number receiving maximum eligible doses 13 (48) 7 (27) Median eligible doses 4 (1.5–5) 3 (1.25–3) Median received 2 (1–3) 1 (1–1) Protection Median time to initiation, weeks (IQR) 0 (0–5) 6.3 (0.9–6.6) 0.002 Median proportion of season covered (%) 59.3 (30–88) 31 (31–52) 0.2 Respiratory admissions Respiratory admissions, n (%) 5 (19) 7 (27) 0.5 RSV admissions, n (%) 2 (7) 0 (0) 0.2 The median delay to initiation in 2020/2021 was more than 6 weeks. The uncertainty regarding the timing and trajectory of the atypical RSV 2020/2021 season contributed to the delay. There is currently no accepted method to define the onset and offset of the RSV season.4 The 10% positivity method used at our institution is overly influenced by contemporary testing practices and cocirculating viruses, factors that have significantly changed by the emergence of severe acute respiratory syndrome coronavirus 21. A prospective method, such as the moving epidemic method, may offer a more stable signpost of an emerging out of season surge.4 There was a delay in palivizumab administration and lower season coverage in the 2020/2021. With uncertainty regarding ongoing RSV seasonality, monitoring of RSV cases and a clinically appropriate, real-time definition for the onset and offset of RSV seasons needs to be established to provide an agile, timely, and accurate timing for administration of palivizumab for high-risk infants.