Impact of the first COVID-19 lockdown on HIV diagnosis in England: an observational time series study

Background: Sexually transmitted infections (STIs) and Human Immunodeficiency Virus (HIV) prevention and care services in England were unavoidably disrupted by the Coronavirus Disease of 2019 (COVID-19) lockdowns, and it is likely incidence was also affected. Estimates of HIV incidence rely on data on trends in new diagnoses, so understanding how much these diagnosis trends changed during lockdown is crucial for estimating incidence. Methods: We estimated the magnitude of the effect of the first United Kingdom (UK) national COVID-19 lockdown in March 2020 on subsequent HIV diagnoses, using the quarterly time series of observed diagnoses during the period 2004 to 2020. Using a Bayesian structural time series model we estimated the counterfactual number of new HIV diagnoses in the post-lockdown period that would have occurred in the absence of lockdown. This counterfactual was constructed using ''synthetic controls'', time series correlated with HIV diagnoses pre-lockdown that were themselves unaffected by the lockdown, based on Google Trend data. The effect was estimated as the difference between the counterfactual and the observed number of diagnoses, for strata defined by gender, sexual orientation, age, and whether or not the diagnosis was late. Results: All strata had greater than 50% posterior probability that the first COVID-19 lockdown had an effect on HIV diagnosis, with the highest posterior probability of an effect (99%) in heterosexual men aged 50+ with late diagnosis. The estimated overall number of missed diagnoses was 97 (95% prediction interval [-688, 850]). We found that the effect size varied by stratum and by time since the lockdown, with the largest effect in the first quarter after the lockdown. The effect then reduced, as HIV testing, and consequent diagnosis, caught up during the summer of 2020. Conclusions: As the number of new HIV diagnoses made in England and estimated incidence fell consistently in the five years pre-pandemic, we hypothesise that the effect of the lockdown may have been less pronounced than it could have been if the epidemic had not already been in decline. Public health campaigns which encouraged HIV home testing during and after the lockdown may also have helped to mitigate the effect.