VACCINATING all adults in the UK against Covid is unlikely to achieve herd immunity and fully contain the virus, even if the vaccine is highly protective against infection, a new study has warned.
Modelling published today in the journal, Lancet Infectious Diseases, concludes that a gradual release of restrictions is needed alongside a high vaccine uptake to minimise future waves of infection.
Long-term use of face coverings and contact tracing following large public events "may be necessary for some time".
The researchers predict that partially easing restrictions across the UK in April 2021 compared to delaying it until June 2021 will result in 7,500 extra Covid deaths by January 2024, even if the vaccine is 85 per cent effective at protecting people against infection.
The only scenario where case numbers remain low is if all control measures remain in place until January 2022 with high vaccine uptake in all age groups, and a vaccine providing 85% protection against infection.
However, realistically they recommend a gradual easing of measures.
An end to restrictions in autumn - when the entire adult population is expected to have had two vaccine doses - rather than in summer is predicted to result in a 10-fold reduction in deaths, from a peak of 430 per day to 46 per day.
Scotland's current roadmap out of lockdown anticipates lowering restrictions to 'Level 0' by the end of June.
This is unlikely to mean a complete end to public health measures, but exactly what it means - such as requirements for face coverings or limits on the number of households which can mix at any one time - remains under review.
The authors, from Warwick University, caution that the modelling does not take into account the emergence of new variants resistant to vaccines or waning immunity requiring a booster inoculation.
However, it was also done before early real-world data from vaccination rollout studies.
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Professor Matt Keeling, co-author of the study, said: “Our modelling suggests that vaccination rollout in adults alone is unlikely to completely stop Covid-19 cases spreading in the UK.
"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.”
This study modelled the impact of the UK vaccination rollout against different scenarios of relaxing control measures.
They used this to estimate the R number, deaths and hospital admissions for Covid from January 2021 to January 2024.
The model assumed vaccine uptake would be 95% in those aged 80 years and older, 85% in those aged 50–79 years, and 75% in those aged 18–49 years, but also modelled for scenarios where uptake was higher (95% in the over 80s and 85% for adults under 50) or lower (90% and 70% respectively).
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To date in Scotland, uptake has exceeded 97% for everyone aged 65 and over, with the rollout continuing for the over-50s.
Vaccine protection against symptomatic disease was assumed by the authors to be 88% based on clinical trials of both Pfizer and AstraZenenca vaccines.
Since the vaccines’ protection against infection is still uncertain, it was modelled at various levels: 0%, 35%, 60%, and 85%.
Recent real-world data from healthcare workers in Scotland indicates that protection may be around 60%.
Even under the most optimistic scenario, however, the R number was estimated to remain around 1.58 if all other controls on the virus were removed.
This would enable the epidemic to spread rapidly, resulting in "another wave of infections with a substantial number of deaths" because not everyone is vaccinated and no vaccine is 100% effective in preventing infection and serious illness.
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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.
The remaining 36% would occur in the minority of the population who have not been vaccinated at all.
Dr Sam Moore, from University of Warwick, said: “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.”
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