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The SARS-CoV-2 pandemic has severely affected international travel. With efficacious COVID-19 vaccines available, Qatar implemented a pilot program between February 18 and April 26, 2021, to ease travel restrictions by waiving the quarantine requirement for vaccinated residents who received their second vaccine dose at least 14 days before arrival. The program still required a polymerase chain reaction (PCR) test to be performed on each passenger upon arrival at Hamad International Airport, Qatar’s international travel gate. We investigated the incidence of PCR-positive test results in arriving passengers.

Methods

All PCR test data for residents arriving on international flights, regardless of departure country and vaccination status, throughout the program (February 18-April 26, 2021) were analyzed. TaqPath COVID-19 combo kits (100% sensitivity and specificity; Thermo Fisher Scientific¹) are used for more than 85% of PCR testing in Qatar. PCR methods are detailed in the eMethods in the Supplement. PCR test results, vaccination records, and related demographic details were retrieved from the integrated nationwide digital health information platform that hosts the national centralized SARS-CoV-2 databases, and which includes all PCR testing and vaccination records in Qatar since the pandemic began (Supplement).

We assessed whether vaccination (using the BNT162b2 [Pfizer-BioNTech] or mRNA-1273 [Moderna] vaccines) and prior infection were associated with lower risk for testing PCR positive. PCR positivity in vaccinated persons and those with a documented prior infection was compared with PCR positivity in those with no record of vaccination or prior infection after one-to-one matching by age, sex, nationality (>40 nationalities), and testing date to control for differences in exposure risk² and SARS-CoV-2 variant exposure.³ Fully vaccinated was defined as at least 14 days after the second dose before the airport PCR test. Reinfection was defined as the first PCR-positive swab at least 90 days after a prior infection. Individuals with a PCR-positive swab less than 90 days before the airport PCR test and vaccinated persons who received only 1 dose or who did not present at least 14 days after the second dose before the airport PCR test were excluded.

Frequency distributions and central tendency measures were generated. Associations with PCR positivity were investigated using relative risks and associated 95% CIs and χ² tests. Two-sided P ≤ .05 indicated statistically significant evidence for an association. Analyses were performed using STATA/SE version 16.1.

Variants were ascertained using viral genome sequencing of randomly collected PCR-positive specimens from arriving passengers.⁴

This study was approved by Hamad Medical Corporation and Weill Cornell Medicine-Qatar institutional review boards with a waiver of informed consent.

Results

In total, 261 849 persons (75.1% male) were tested using PCR for SARS-CoV-2 upon arrival at the Qatar airport. Median age was 33 years (interquartile range, 27-41 years). Of 31 190 completely vaccinated individuals (group 1; 99.7% with BNT162b2 and 0.3% with mRNA-1273) and 215 901 individuals with no record of vaccination or prior infection (group 2), 10 092 could be matched, among whom PCR positivity was 0.82% (95% CI, 0.66%-1.01%) and 3.74% (95% CI, 3.37%-4.12%), respectively (Figure).

Of 9180 individuals with no record of vaccination, but a record of prior infection at least 90 days before the PCR test (group 3), 7694 could be matched to individuals with no record of vaccination or prior infection (group 2), among whom PCR positivity was 1.01% (95% CI, 0.80%-1.26%) and 3.81% (95% CI, 3.39%-4.26%), respectively (Figure).

The relative risk for PCR positivity was 0.22 (95% CI, 0.17-0.28) for vaccinated individuals and 0.26 (95% CI, 0.21-0.34) for individuals with prior infection compared with no record of vaccination or prior infection (Table).

Sequencing of 72 PCR-positive specimens from arriving passengers identified B.1.351 (beta; n = 32; 44.4%), B.1.1.7 (alpha; n = 20; 27.8%), B.1.617 (delta; n = 8; 11.1%), and “wild-type” strains (n = 12; 16.7%).

Discussion

Vaccination and prior infection were associated with reduced risk for SARS-CoV-2 PCR test positivity in residents of Qatar returning on international flights. Nevertheless, both vaccine immunity and natural immunity were imperfect, with breakthrough infections recorded. This highlights the need to maintain PCR testing for arriving travelers.

Limitations include ascertainment of prior infection history using records of previous PCR-positive results, thereby missing those who had prior mild or asymptomatic infections, but were never tested. Findings may not be generalizable to other airports, regions, or domestic travel.