We did an multi-centre, observational cohort study in patients who had surgery in 2023. We included participants who underwent surgery after the COVID-19 to lift the lockdown in China. Patients meeting the same criteria were eligible who had been treated during the same calendar period of 2019 through 2021. The primary outcomes were the post-operative in-hospital complications. We hypothesized that the post-operative in-hospital complications during the COVID-19 to lift the lockdown period in China were different to complications for the same kind of patients during the same calendar period of the previous years.

The outbreak of COVID-19 and its global pandemic have posed a threat to public health. The deadly virus, SARS-CoV-2, has been evolving to new, more infectious variant and other lineages with additional immune escape mutations. The highly transmissible Omicron variant has been present for around one year and has supplanted Delta as the leading strain in the global pandemic. Despite the fact that 656 million people have been infected with SARS-CoV-2 worldwide as of January 1, 2023, asymptomatic infections and mild cases account for more than 90% because of its notably declined pathogenicity.As of December 20, 2022, more than 130 sub-branches of Omicron have been imported into China, with BA.5.2 and BF.7 being the most prevalent strains.

On December 7, 2022, the State Council of China issued an announcement on further optimization of measures for preventing and controlling the COVID-19 epidemic ( easing of rigorous "zero COVID" policies). Since then, the rapid spread of COVID-19 has caused a surge of COVID-19 infections in the majority of China. As of January 6, a total of 503302 individuals have been infected. Consequently, the proportion of surgical patients with current or previous SARS-CoV-2 infections will inevitably increase within a short period of time. It has been reported that recovery from SARS-CoV-2 infection is associated with a transiently elevated risk of postoperative complications. The longer the time interval between SARS-CoV-2 infection and surgery, the lower the risk of postoperative complications. An updated recommendation suggested postponing surgery for at least seven weeks following SARS-CoV-2 infection, thereby reducing the risk of postoperative complications and 30-day mortality to baseline levels (similar risk with patients without a history of SARS-CoV-2 infection). However, these recommendations were based on limited data from the earlier Covid-19 pandemic (mostly caused by the Delta strain) in Europe and the United States It may not be feasible to generalize and apply this experience and consensus to the Chinese population and use it to guide current practice.

In this prospective cohort study, the postoperative complications will be described and compared in patients with or without Covid-19 infection. In addition, risk factors in the patients and surgical levels that are associated with an increase in postoperative morbidities and mortalities will be assessed.

Inclusion Criteria:

• Underwent surgery at Xijing Hospital after the COVID-19 to lift the lockdown in China, effective as of 29th December in 2022 to 7th January in 2023.

Exclusion Criteria:

• Patients who had missing primary information data (i.e., postoperative information).

The exposure of interest was a diagnosis of COVID-19 viral infection defined using the the process of experiencing typical COVID-19 symptoms, or swab-test positive (either PCR or rapid antigen SARS-CoV-2 test). Patients with COVID-19 were categorised as symptomatic if they had concomitant respiratory illness or indicating respiratory support.