Time from last immunity event against infection during Omicron-dominant period in Malaysia

Area of Science:

• Infectious Diseases
• Epidemiology
• Vaccinology

Background:

• The Omicron variant of SARS-CoV-2 emerged as a dominant strain, necessitating an understanding of its transmission dynamics and protective factors.
• Healthcare workers represent a critical population for monitoring infectious disease incidence due to their occupational exposure risks.

Purpose of the Study:

• To determine the incidence of Omicron infections among healthcare workers in Malaysia.
• To identify exposures, such as prior SARS-CoV-2 infection and vaccination status, that mitigate the risk of Omicron infection.

Main Methods:

• A multicenter, prospective cohort study was conducted involving 482 healthcare workers in Malaysia.
• Participants received two or three doses of the BNT162b2 vaccine during the Omicron-dominant period (January 31 to July 31, 2022).

Main Results:

• The cumulative incidence of Omicron infection was 44.6%, with an incidence rate of 3.33 per 1000 person-days.
• Previous SARS-CoV-2 infection was associated with a significantly lower hazard of Omicron infection (HR 0.41).
• Recent immunity events (within 30 days) offered greater protection compared to events over 90 days prior (HR 3.82).

Conclusions:

• Natural infection with SARS-CoV-2 prior to the Omicron wave conferred significant protection against subsequent Omicron infection.
• Maintaining recent immunity, likely through vaccination or recent infection, is crucial for protection against Omicron variant infections.