Vaccinating all adults in the UK is unlikely to achieve herd immunity and fully contain the coronavirus, according to a modelling study published in The Lancet Infectious Diseases Journal. A gradual release of control measures, high vaccine uptake, and a vaccine with high protection against infection is essential to minimise future waves of infection, the authors said.
The analysis was done before early real-world data from vaccination rollout studies. Preliminary findings suggest that vaccination does offer a level of protection against infection, but the exact level is still unclear. For this reason, the authors examined 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.
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 model assumed vaccine uptake would be 95% in those aged 80 and older, 85% in those aged 50–79, and 75% in those aged 18–49. Vaccine protection against symptomatic disease was assumed to be 88% based on phase 3 trial data from the Pfizer-BioNTech and Oxford-AstraZeneca vaccines being administered in the UK. The vaccines’ protection against infection was varied in four scenarios (0%, 35%, 60%, 85%).
According to the researchers, 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.
As vaccination alone is not expected to drive R below 1, removing all restrictions after the vaccination rollout is complete is predicted to lead to another wave of infections with a substantial number of deaths. The scale of future waves and the number of deaths is influenced by how early and over what time-scales measures are relaxed, the vaccine’s level of protection against infection, and vaccine uptake.
The authors considered abrupt releases of some measures (from current restrictions to a situation comparable to September 2020) with a vaccine that offers 85% protection and calculated the number of deaths from January 2021 until January 2024. A partial release in February 2021 was estimated to lead to 130,100 deaths by January 2024, whereas partial release in April 2021 lowers this to 61,400 deaths and partial release in June 2021 to 53,900 deaths, highlighting the impact of the vaccination programme rollout. These estimates all include the 49,300 deaths that have already occurred this year.