Boris Johnson’s government is pushing back the release of lockdown restrictions in England by four weeks, despite the UK being in the top 10 countries with the highest percentage of vaccine doses administered. Reasonably, people are asking: why the need for prolonged restrictions when the rollout has been so successful? What does a safe level of vaccination look like? To date, 46.8% of the population are fully vaccinated in the UK and 64.2% have received one dose of a coronavirus vaccine. The jabs approved in the UK use the virus’s spike protein to educate our immune system so when it meets the real thing, it can produce antibodies and T-cells that recognise this spike and control the infection. After the first vaccination (or natural infection) it takes a couple of weeks to expand the relevant immune cells, but then memory cells protect us from severe disease in future infections. In previously infected people, the first vaccination acts like a booster, helping them retain antiviral immunity for longer. Immunological memory duration differs for different viruses, and this is why we need to monitor how long protection lasts for new vaccines and viruses, enabling us to work out when we need booster vaccinations. The second vaccination in two-dose regimens acts to increase the power and duration of immunity after the first jab. We appreciate that immunity may wane a few months to a year after coronavirus infection, but the timing of this has yet to be established following vaccination. Given the pressing clinical need and early sparsity of vaccine doses, the initial decision was taken to vaccinate at an interval of 12 weeks for two-dose vaccines. This helped us protect the most vulnerable faster, despite some vaccines being tested only at eight-week intervals in clinical trials. The latest advice is to bring forward the second jab appointments to eight weeks, to help keep us safe from a third wave of infection. Vaccines, however, are not magic; they do nothing to stop us being exposed to a virus if someone sneezes over us, and this is why restrictions still play a role. Vaccines do help reduce the opportunities for the virus to take hold and the intensity of an infection’s aftermath, while cutting down transmission. So far, they are estimated to have saved 12,000 lives in England alone, and prevented more than 30,000 hospitalisations. Most vaccinated people will show mild symptoms or none at all when infected. But symptoms may also depend on the variant. There is still a chance that vaccinated people will pass the virus on, particularly at super-spreader events and with highly transmissible variants, such as the Delta variant now predominant in the UK. As new variants that carry mutated spike proteins emerge, the effect of our current jabs may be reduced and the vaccines will require updating. But right now, there is evidence that our vaccines are protective against the Delta variant. So what does a safe level of vaccination look like, in order to protect those unable to have a jab and achieve herd immunity? It depends on the virus, and this coronavirus has a few tricks up its sleeve. At the beginning of the pandemic, experts estimated that about 70% of the population needed to be vaccinated to keep everyone safe from severe disease, but the Delta variant is more transmissible than the original virus, and the new estimate is closer to 85%. We are on the right track, with cautious restrictions and extending the vaccine rollout, and upcoming school closures for the summer are on our side. We have to continue taking personal precautions to stop the spread, or new variants will emerge that will eventually escape the vaccines we have now. We are also rightly planning for a booster jab programme in the autumn, which itself raises questions, such as how to safely combine Covid vaccinations with winter flu jabs. The aim is to reduce the risk as much as possible for everyone; we don’t yet fully understand long Covid, or the impact of infection on tissues such as the brain. Until the majority of us are fully protected and infection rates are brought back under control, I will continue to wear my mask in busy places and indoors after restrictions are lifted. We must do all we can to protect the effectiveness of our vaccines for as long as possible, or we will find ourselves back at square one. I will also continue to monitor immunity in vaccinated people, because we don’t know yet how long protection will last. When immunity starts to wane, we need to detect this through immune surveillance tests and invite those who are vaccinated to get booster jabs of the same or updated vaccines, as needed, in the years to come. There is still some way to go out of this pandemic. Dr Zania Stamataki is a senior lecturer and researcher in viral immunology at the University of Birmingham