Impact of the COVID-19 related border restrictions on influenza and other common respiratory viral infections in New Zealand

Abstract

Background: New Zealand's (NZ) complete absence of community transmission of influenza and respiratory syncytial virus (RSV) after May 2020, likely due to COVID-19 elimination measures, provided a rare opportunity to assess the impact of border restrictions on common respiratory viral infections over the ensuing 2 years.

Methods: We collected the data from multiple surveillance systems, including hospital-based severe acute respiratory infection surveillance, SHIVERS-II, -III and -IV community cohorts for acute respiratory infection (ARI) surveillance, HealthStat sentinel general practice (GP) based influenza-like illness surveillance and SHIVERS-V sentinel GP-based ARI surveillance, SHIVERS-V traveller ARI surveillance and laboratory-based surveillance. We described the data on influenza, RSV and other respiratory viral infections in NZ before, during and after various stages of the COVID related border restrictions.

Results: We observed that border closure to most people, and mandatory government-managed isolation and quarantine on arrival for those allowed to enter, appeared to be effective in keeping influenza and RSV infections out of the NZ community. Border restrictions did not affect community transmission of other respiratory viruses such as rhinovirus and parainfluenza virus type-1. Partial border relaxations through quarantine-free travel with Australia and other countries were quickly followed by importation of RSV in 2021 and influenza in 2022.

Conclusion: Our findings inform future pandemic preparedness and strategies to model and manage the impact of influenza and other respiratory viral threats.

Keywords: acute respiratory illness; common respiratory viral infections; influenza infection; public health and social measures; respiratory syncytial viral infection; severe acute respiratory infections.

FIGURE 1

Timeline of New Zealand's border restrictions. ¹Border closure = borders close to all but New Zealand citizens and permanent residents. For those allowed to enter, they are required to comply with mandatory government‐managed isolation and quarantine (MIQ) in designated facilities on arrival. PHSMs, public health and social measures.

FIGURE 2

Temporal distribution of acute respiratory infections (ARIs) and associated influenza, RSV, and rhinovirus detections with (2020–2022) and without (2019) border restrictions. Panel 1: P1.A. Hospital‐based severe acute respiratory infection incidence rate, P1.B. RSV ‐associated SARI, P1.C. Influenza ‐associated SARI, P1.D. Rhinovirus‐associated SARI. Panel 2: P2.A. SHIVERS‐II, ‐III and ‐IV cohort‐based ARI incidence rate, P2.B. RSV‐associated ARI/ILI, P2.C. Influenza‐associated ARI/ILI, P2.D. Rhinovirus‐associated ARI/ILI. Panel 3: P3.A. ILI consultations among HealthStat GP patients, P3.B. RSV‐associated ARI among SHIVERS‐V GP patients, P3.C. Influenza‐associated ARI among SHIVERS‐V GP patients, P3.D. Rhinovirus‐associated ARI among SHIVERS‐V GP patients. Panel 4: P4.1. Lab‐based RSV, P4.2. Lab‐based influenza, P4.3. Lab‐based rhinovirus detection. GP, general practice; ILI, influenza‐like illness; PHSMs, public health and social measures; SARI, severe acute respiratory infection; SHIVERS‐II, ‐III, ‐IV and –V, the 2nd, 3rd, 4th, 5th iterations of the southern hemisphere influenza and vaccine effectiveness research and surveillance programme. The calculation for epidemic threshold and influenza activity are described in the Section 2. A patient with cough and history of fever (subjective fever or measured temperature ≥38°C) and onset within the past 10 days meets the SARI case definition if hospitalised or meets the ILI case definition if participating in the SHIVERS‐II and ‐III study during 2019. The ARI case definition among SHIVERS‐II, ‐III, ‐IV and ‐V participants refers to an “acute respiratory illness with fever or feverishness and/or one of following symptoms (cough, runny nose, wheezing, sore throat, shortness of breath, loss of sense of smell/taste) with onset in the past 10 days”. Partial border relaxation 1 refers to brief introduction of quarantine‐free travel with Australia during 19 April 2021 to 22 July 2021. Partial border relaxation 2 refers to progressive border relaxation between 28 Feburary 2022 to 31 July 2022. Introduction of quarantine‐free travel initially for vaccinated New Zealanders from Australia on 28 Feburary 2022 and for the same groups from the rest of the world on 13 March 2022, then for vaccinated Australians from 13 April 2022 and vaccinated travellers from NZ's visa‐waiver countries from 2 May 2022 onwards.

FIGURE 3

Temporal distribution of influenza and respiratory syncytial virus (RSV) associated acute respiratory infections (ARI) among travellers during 2021–2022. The ARI case definition among travellers refers to an “acute respiratory illness with fever or feverishness and/or one of following symptoms (cough, running nose, wheezing, sore throat, shortness of breath, loss of sense of smell/taste) with onset in the past 10 days.”

FIGURE 4

Temporal distribution of other respiratory viral detections during 2020–2022 compared with the reference period of 2015–2019 for adenovirus, enterovirus, and human metapneumovirus (hMPV) or the reference period of even‐numbered* years (2010, 12, 14, 16, 18) or odd‐numbered* years (2011, 13, 15, 17, 19) for parainfluenza virus types 1–3. (A) Lab‐based adenovirus detection. (B) Lab‐based enterovirus detection. (C) Lab‐based human metapneumovirus (hMPV) detection. D Lab‐based parainfluenza virus type 1 (PIV1) detection. (E) Lab‐based parainfluenza virus type 2 (PIV2) detection. (F) Lab‐based parainfluenza virus type 3 (PIV3) detection. (*note: in NZ, PIV1 activity occurred during even‐numbered years while PIV2 activity in odd‐numbered years and PIV3 activity annually. For laboratory‐based PIV1–3 detections during 2003–2022, see supplementary Figure S1).