evidence: With a circuit breaker, authorities tighten restrictions on what people can do for a set amount of time to reduce transmission of the virus, to try to avoid needing to go into full lockdown. Northern Ireland’s four-week plan includes closing all bars and restaurants (except for takeaways), stopping indoor amateur sports, and shutting close-contact services such as hairdressing. [...] There’s also much more travel from Northern Ireland across the land border with the Republic of Ireland than to rest of the UK. Because the Republic of Ireland implemented a lockdown earlier than the UK and had additional restrictions on movement and travel, this may have limited the number of new infections brought into Northern Ireland. [...] With this in mind, the longer the restrictions are in place, the more effective they’ll be at reducing viral spread. It’s important for the circuit breaker to remain in place longer than the upper end of the potential incubation period if it’s to have a good chance of significantly reducing the rate of transmission. It’s good therefore that Northern Ireland has opted for a four-week set of restrictions.