“Immunity Passports” for SARS-CoV-2: an online experimental study of the impact of antibody test terminology on perceived risk and behaviour
Authors: Waller Jo , Rubin G. James , Potts Henry W. W. , Mottershaw Abi , Marteau Theresa M 
Published: May 2020

WHAT IS ALREADY KNOWN ON THIS TOPIC

Test results indicating the presence of antibodies to SARS-CoV-2 are often referred to as Immunity Passports or Certificates.

Due to the limitations of such tests, including uncertainty about the duration of immunity conferred by detected antibodies, those receiving results indicating the presence of antibodies retain a risk of becoming infected by SARS-CoV-2.

It is unknown whether the use of the terms Immunity Passports or Certificates reduces awareness of the residual risk inherent in an antibody-positive test result and adherence to protective behaviours, thereby increasing risk of transmission.

WHAT THIS STUDY ADDS

Using the term Immunity - as opposed to Antibody - to describe antibody tests for SARS-CoV-2 more than doubled the proportion who erroneously perceived they would have no risk of catching coronavirus in the future given an antibody-positive test result, from 9.8% for Antibody to 19.1% for Immunity.

Perceiving no risk of infection with coronavirus given an antibody-positive test result was associated with an intention to wash hands less frequently.

Using the terms Passport, Certificate or Test had no significant effect.

Objective:

To assess the impact of describing an antibody-positive test result using the terms Immunity and Passport or Certificate, alone or in combination, on perceived risk of becoming infected with SARS-CoV-2 and intention to continue protective behaviours.

Design:

2 × 3 experimental design.

Setting:

Online with data collected between 28th April and 1st May 2020.

Participants:

1,204 adults registered with a UK research panel.

Intervention:

Participants were randomised to receive one of six descriptions of an antibody test and results showing SARS-CoV-2 antibodies, differing in the terms used to describe the type of test (Immunity vs Antibody) and the test result (Passport vs Certificate vs Test).

Main outcome measures:

The primary outcome was the proportion of participants perceiving no risk of becoming infected with SARS-CoV-2 given an antibody positive test result. Other outcomes include intended changes to frequency of handwashing and physical distancing.

Results:

When using the term Immunity (vs Antibody), 19.1% of participants [95% CI: 16.1 to 22.5] (vs 9.8% [95% CI: 7.5 to 12.4]) perceived no risk of catching coronavirus at some point in the future given an antibody-positive test result (AOR: 2.91 [95% CI: 1.52 to 5.55]). Using the terms Passport or Certificate – as opposed to Test – had no significant effect (AOR: 1.24 [95% CI: 0.62 to 2.48] and AOR: 0.96 [95% CI: 0.47 to 1.99] respectively). There was no significant interaction between the effects of the test and result terminology. Across groups, perceiving no risk of infection was associated with an intention to wash hands less frequently (AOR: 2.32 [95% CI: 1.25 to 4.28]) but there was no significant association with intended avoidance of physical contact with others outside of the home (AOR: 1.37 [95% CI: 0.93-2.03]).

Conclusions:

Using the term Immunity (vs Antibody) to describe antibody tests for SARS-CoV-2 increases the proportion of people believing that an antibody-positive result means they have no risk of catching coronavirus in the future, a perception that may be associated with less frequent handwashing. The way antibody testing is described may have implications for the likely impact of testing on transmission rates.

Study registration:

Open Science Framework: https://osf.io/tjw78/files/