(284) The Effectiveness of Single and Two-Dose Pfizer-BioNTech Vaccine: A Real-World Evidence from Saudi Arabia

Sunday, August 28, 2022

8:00 AM – 1:45 PM CEST

Location: Hall C

Publication Number: 1329

Presenting Author(s)

Yasser Albogami, PhD
– Assistant Professor, King Saud University, Riyadh, Saudi Arabia

Co-Author(s)

Abdulaziz Alalwan
– Family Medicine Department, King Saud University Medical City, Riyadh, Saudi Arabia, Saudi Arabia
Mohammed A. Batais
– Department of Family and Community Medicine, College of Medicine, King Saud University, Riyadh, Saudi Arabia, Saudi Arabia
Khaled Alabdulkareem
– Assisting Deputyship for Primary Health Care, Ministry of Health, Riyadh, Saudi Arabia, Saudi Arabia
Abdullah Abdulaziz Alalwan
– Assistant Professor of Pharmacoepidemiology and Drug Safety, Qassim University, Saudi Arabia, Riyadh, Al Riyadh, Saudi Arabia

Background: The control of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has been a global major concern. Several vaccines proved effectiveness against SARS-COV-2; however, the number of doses and the period between doses that warrant the highest protection remain unclear.

Objectives: This study aims to assess the effectiveness of the Pfizer-BioNTech vaccine and to evaluate the effectiveness of early and delayed second-dose administration of the vaccine.

Methods: We included students and staff of King Saud University who have never been infected with SARS-CoV-2 from March 1st, 2021, to August 31st, 2021. Data regarding vaccination coverage and confirmed SARS-CoV-2 infection were obtained using King Saud University Medical City databases and Health Electronic Surveillance Network (HESN) platform.
Exposure: Time-varying vaccination status (categorized as: unvaccinated, vaccinated 1st dose, and vaccinated 2nd dose) were measured. We only included Pfizer-BioNTech vaccine.
Main Outcomes and Measures: The outcome of interest was a confirmed positive polymerase chain result test for SARS-CoV-2. A generalized linear model with a Poisson distribution was used to estimate the incidence of the infection.

Results: Among 66,775 participants included, 2615 SARS-CoV-2 infections were observed. The sample was relatively young with average age of 25 years and 43% female. The incidence rate of SARS-CoV-2 infections among unvaccinated was 46 per 100,000 person-years. A single dose of Pfizer-BioNTech vaccine had 40% effectiveness. The vaccine effectiveness doubled after the second dose of Pfizer-BioNTech (80%). The time between the first and second dose appears to be crucial after observing 75%, 90% and 85% effectiveness with early vaccination, on-time vaccination, and delayed vaccination, respectively.

Conclusions: For Pfizer-BioNTech vaccine recipients in Saudi Arabia, higher effectiveness against SARS-CoV-2 was observed with two doses of the vaccine. The timing of the second dose of the vaccine appears to be a dominant factor to the extent of protection against SARS-CoV-2.