Introduction: Nebulizers used to deliver aerosol during non-invasive mechanical ventilation (NIV) have many types, each type has many different designs. This study aimed to determine the effect of nebulizer deign on aerosol delivery in NIV. Methods: Different designs of jet nebulizer (JN) and vibrating mesh nebulizer (VMN) were tested by placing 1 ml of salbutamol in a nebulizer chamber operated in an in vitro NIV setting using a breathing simulator with adult settings (inhalation-exhalation ratio 1:3, 15 breaths/

Coronavirus disease 2019 (COVID‐19) has had different waves within the same country. The spread rate and severity showed different properties within the COVID‐19 different waves. The present work aims to compare the spread and the severity of the different waves using the available data of confirmed COVID‐19 cases and death cases. Real‐data sets collected from the Johns Hopkins University Center for Systems Science were used to perform a comparative study between COVID‐19 different waves in 12 countries with the highest total performed tests for severe acute respiratory syndrome coronavirus 2 detection in the world (Italy, Brazil, Japan, Germany, Spain, India, USA, UAE, Poland, Colombia, Turkey, and Switzerland). The total number of confirmed cases and death cases in different waves of COVID‐19 were compared to that of the previous one for equivalent periods. The total number of death cases in each wave was presented as a percentage of the total number of confirmed cases for the same periods. In all the selected 12 countries, Wave 2 had a much higher number of confirmed cases than that in Wave 1. However, the death cases increase was not comparable with that of the confirmed cases to the extent that some countries had lower death cases than in Wave 1, UAE, and Spain. The death cases as a percentage of the total number of confirmed cases in Wave 1 were much higher than that in Wave 2. Some countries have had Waves 3 and 4. Waves 3 and 4 have had lower confirmed cases than Wave 2, however, the death cases were variable in different countries. The death cases in Waves 3 and 4 were similar to or higher than Wave 2 in most countries. Wave 2 of COVID‐19 had a much higher spread rate but much lower severity resulting in a lower death rate in Wave 2 compared with that of the first wave. Waves 3 and 4 have had lower confirmed cases than Wave 2; that could be due to the presence of appropriate treatment and vaccination. However, that was not reflected in the death cases, which were similar to or higher than Wave 2 in most countries. Further studies are needed to explain these findings.

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