Impact of vaccination on risk of international air travel
In summer 2020, the UK government established travel corridors between the UK and a small number of countries that posed a low COVID-19 risk. In early 2021, new policies were introduced for passengers entering the UK amid worries around variants of concern. At the same time, the UK started to roll out its vaccination programme, which has currently provided a dose of the vaccine to over 32m adults and is set to vaccinate most of the adult population by the end of July.
Currently approved vaccines, including those from Pfizer and AstraZeneca, have achieved high effectiveness in reducing severe illness. When this success is combined with higher-than-expected levels of uptake in the community, the anticipated impact on potential hospitalisations and deaths is substantial.
The second benefit is the impact on hospitalisation and deaths. On these critical metrics, the vaccinations perform highly, often above 95% after two doses. The targeted roll-out of the vaccine to the most vulnerable will mean that the likelihood of a vaccinated population needing hospitalisation or dying reduces to 1.2% and less than 0.1%, respectively, from early June.
When both benefits are taken together, the effect of the vaccination programme is substantial. Based on the risk level established by previous travel corridors, prevalence in origin countries could be three times higher without changing domestic COVID-19 risk from air passengers. With pre-departure/on-departure testing, the threshold could increase by a factor of between six and eight.
While we use estimates of actual prevalence in our analysis, these ratios could be applied to reported incidence or prevalence in origin countries as the government develops thresholds for new travel corridors. For example, if an incidence of 20 cases per week per 100,000 people were previously accepted as a threshold for travel corridors, this threshold could be increased to 60 per 100,000 without testing and 160 per 100,000 by the end of June. By the end of May (as more social distancing is expected to be in place), this would be equivalent to 80 per 100,000 or 200 per 100,000.
Based on data from the summer of 2020, we have estimated that prevalence in travel corridor countries was 0.03%. The methodology used to estimate prevalence allows us to account for factors such as under-estimation of asymptomatic cases and death rates. With vaccinations, the prevalence rate of 0.03% could increase to 0.2–0.3% with some form of pre-departure testing. Without any testing, the threshold would increase to 0.1%.
These new thresholds would increase the number of travel corridor countries from 62 to 102. These are illustrative of potential ‘green list’ countries should future travel policies take a tiered approach to risk. If there are requirements for pre-departure testing, the threshold would increase to between 122 and 131 countries. The additional 20 to 29 countries where risk is equalised with pre-departure testing are illustrative of potential ‘amber list’ countries should future travel policies take a tiered-risk approach.