Reducing false reassurance following negative results from asymptomatic coronavirus (Covid-19) testing: an online experiment

Objectives. Individuals who receive a negative lateral flow coronavirus (Covid-19) test result may misunderstand it as meaning no risk of infectiousness, giving false reassurance. This experiment tested the impact of adding information to negative test result messages about (a) residual risk and (b) need to continue protective behaviours. Design. 4 (residual risk) x 2 (post-test result behaviours) between-subjects design. Setting. Online. Participants. 1200 adults from a representative UK sample recruited via Prolific (12-15 March 2021). Interventions. Participants were randomly allocated to one of eight messages. Residual risk messages were: 1) 'Your coronavirus test result is negative' (control); 2) Message 1 plus 'It's likely you were not infectious when the test was done' (Current NHS Test and Trace); 3) Message 2 plus 'But there is still a chance you may be infectious' (Elaborated NHS Test and Trace); 4) Message 3 plus infographic depicting residual risk (Elaborated NHS Test and Trace + infographic). Each message contained either no additional information or information about behaviour, i.e. the need to continue following guidelines and protective behaviours. Outcome measures. (i) proportion understanding residual risk of infectiousness and (ii) likelihood of engaging in protective behaviours (score range 0-7). Results. The control message decreased understanding relative to the current NHS T&T message: 54% vs 71% (AOR=0.37 95% CI [0.22, 0.61], p<.001). Understanding increased with the elaborated NHS T&T (89%; AOR=3.27 95% CI [1.78, 6.02], p<.001) and elaborated NHS T&T + infographic (91%; AOR=4.03 95% CI [2.14, 7.58], p<.001) compared to current NHS T&T message. Likelihood of engaging in protective behaviours was unaffected by information (F(1,1192)=0.43, p=.513), being high (M=6.4, SD=0.9) across the sample. Conclusions. The addition of a single sentence ('But there is still a chance you may be infectious') to current NHS Test and Trace wording increased understanding of the residual risk of infection. Trial registration. Open Science Framework: https://osf.io/byfz3/