Vaccination rollout in adults alone is unlikely to completely stop Covid 19 cases spreading in the UK and early sudden release of restrictions is likely to lead to a large wave of infection, according to a new modelling study.

The research published in The Lancet Infectious Diseases journal found that gradual release of control measures, high vaccine uptake, and a vaccine with high protection against infection is essential to minimise future waves of infection.

This analysis was done before early real-world data from vaccination rollout studies. Preliminary findings suggest that the vaccine does offer a level of protection against infection, but the exact level is still unclear – for this reason the authors examine a range of levels of protection against infection.

The authors note that their model does not account for the emergence of new variants, to which the vaccine might offer less protection, nor for the effects of waning immunity, which might necessitate additional vaccination. They also note that they are unable to look at the effects of relaxing individual control measures.

UK ranks third globally for vaccine doses administered

Professor Matt Keeling, from University of Warwick, UK, said: “We also found that early sudden release of restrictions is likely to lead to a large wave of infection, whereas gradually easing measures over a period of many months could reduce the peak of future waves.

"The huge success of the UK’s vaccine programme so far coupled with the government’s gradual roadmap for easing restrictions are a cause for optimism. However, some measures, such as test, trace, and isolate, good hand hygiene, mask-wearing in high-risk settings, and tracing from super-spreader events, may also be necessary for some time.”

Vaccination may offer a potential exit strategy for the pandemic and the UK currently ranks third globally for the total number of vaccine doses administered. This study modelled the combined interaction of the UK vaccination rollout with different scenarios of relaxing control measures, to predict the R number and deaths and hospital admissions due to Covid-19 from January 2021 to January 2024.

The findings suggest that although vaccination can substantially reduce R, it may not be enough to drive R below 1 without other control measures. Under the most optimistic scenario for protection against infection (85%), the R number is estimated to be 1.58 without other controls.

Gradual relaxation, as opposed to immediate release of control measures, may reduce future waves of infection. For example, partial release of control measures in February, 2021, was predicted to lead to a wave of infection that peaks at 1,670 deaths per day, but gradual release of measures over the course of 5 months or 10 months leads to waves that peak at 430 and 46 deaths per day, respectively.

Although vaccination substantially decreases overall deaths, because no vaccine’s protection against symptomatic disease is 100%, the authors note that some people who have been vaccinated will still die of Covid-19. If the vaccine offers 60% protection against infection, the authors predict that 48% and 16% of deaths may be in individuals who have received one or two doses of the vaccine, respectively.

Dr Sam Moore, from University of Warwick, UK, added: “We’re rapidly learning more about vaccine efficacy as vaccination programmes are rolled out across the world. Since we conducted this study, new evidence suggests there may be a higher level of protection against severe disease offered by both the Pfizer-BioNTech and Oxford-AstraZeneca vaccines than the level we assumed.

"This may reduce the size of future hospital admissions and deaths we estimated, making future waves more manageable for the health service. As for protection against infection, some preliminary findings have suggested that the vaccine does offer a level of protection against infection, but the exact level of protection offered by vaccines is still unclear. We will continue to update our predictions as new data on vaccine efficacy becomes available.”

The authors caution that vaccine uptake is likely to be uneven (clustering among certain households and socioeconomic groups), potentially giving rise to pockets of infection, as control measures are relaxed. They stress the importance of intensive test, trace, and isolate capabilities to target these pockets of infection.