Scientists have stressed vaccinating the most vulnerable people against the coronavirus does not guarantee an early end to the pandemic.
Nearly 2 million people in the UK received their first dose of the two-jab regimen last week, with the government aiming to offer a vaccine to all over 70s, extremely clinically vulnerable individuals, and health and care workers by mid-February.
While an effective immunisation programme has long been hailed as a route back to life as we once knew it, experts have repeatedly stressed vaccines are never perfect and should not be seen as a “silver bullet”.
A model by the University of Edinburgh suggests that with 85% vaccine uptake and a delivery of 2 million doses a week, the UK will unlikely reach herd immunity even once the under-50s have had the jab.
While three coronavirus vaccines are approved in the UK, data so far only demonstrate the jabs reduce disease severity, rather than blocking infection transmission.
Without this information, the scientists stressed slow and gradual relaxation of restrictions is likely key, with a rapid return to normal life predicted to “generate an unacceptably large scale outbreak”.
“Vaccine roll out to priority groups will reduce the burden on the NHS,” said study author Professor Mark Woolhouse.
“After that is over, full release of the entire population from restrictions could result in another wave.
“[Vaccine] coverage is key. If 90%, that leaves about 1 million of the most vulnerable unprotected.
“If we delay full release [of lockdown] until all adults are vaccinated, we’re talking about waiting until September.”
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The scientists modelled 44 scenarios, based on factors like social mixing and the relaxation of restrictions.
The predictions suggest a rapid easing of lockdown would “lead to a huge wave of infection, with many associated hospital admissions and deaths”.
A more gradual relaxation would be “far less risky”, potentially providing an exit strategy “without overwhelming” the NHS.
Hospital admissions and deaths would be further reduced, however, if vaccine uptake exceeded the scientists’ 85% assumption.
A separate modelling study by the University of Warwick has revealed a “wide range of plausible scenarios”.
Under the most optimistic assumption for vaccine roll out, coverage and efficacy, “it will be several months before the population immunity threshold is reached in the UK”.
In a “more pessimistic but plausible” scenario, the coronavirus will become endemic, like seasonal flu.
While flu is vaccinated against every winter, with not everyone being eligible for a free jab, it is said to be much less transmissible than the coronavirus.
When it comes to the coronavirus, the Warwick scientists stressed “full release of the entire population immediately after vaccination of the nine priority groups” would likely result in a “major epidemic with [a] significant number of cases”.
A partial release could reduce patient numbers, “but this may require a very limited lifting of current restrictions”.
A final study by Imperial College London suggests “a large proportion of the UK population is still susceptible to the virus”, estimating just under one in five (19%) people have been infected.
“For a pathogen with a basic reproduction number R of around 2.9, around two thirds of the population need to be protected (through immunity following natural infection or immunisation) to bring R below 1,” according to the team.
R describes the number of people a patient is expected to pass the virus on to, in this case 2.9 individuals.
R has been made more complex by the emergence of new coronavirus variants, with the so-called Kent variant thought to increase transmission by up to 70%. All the above models accounted for the new variants.
Virus control is also being affected by the high number of cases, with 38,905 people testing positive in the UK alone on 20 January.
“The impact of any future programme depends on the starting point,” wrote the Imperial scientists.
“Before being able to maintain low level of the damaging outcomes of infections by [the coronavirus], we need to get back to low levels.
“Current levels are extremely high, have been high for a long period and some indicators are likely to remain high for some period of time (hospitalisation, deaths, ICU occupancy) even if others might decrease more rapidly (new cases).”
When it comes to vaccines, none of the three approved jabs are 100% effective at preventing severe disease, with their effect on transmission being unclear.
The Imperial scientists estimated that in order to achieve herd immunity, vaccine uptake must exceed 80%.
“Even with a very ambitious programme of 3 million doses per week, it will take four to five months to cover 80% of the population with their first dose,” they wrote.
“Immune response takes time to build up; [the] effect of [the] first dose will take about two weeks.”
Speaking of the UK’s vaccine programme, study author Dr Anne Cori added: “It is a magic tool but not a magic bullet in that its effect is not instantaneous.
“The impact of vaccination will only be seen once we get very huge coverage, which depends on how fast we roll it out and how many people take it.
Across all the scenarios the team modelled, “full-lifting of NPIs [non-pharmaceutical interventions] before the summer will lead to prolonged and potentially multiple periods of pressure on hospitals, and substantial additional deaths”.
“Partial lifting of NPIs before numbers in hospital have dropped substantially will have the same consequences,” concluded the scientists.
“Lifting NPIs with a manageable impact on the NHS will take weeks to achieve, and will depend on the speed of vaccine roll-out and uptake .
“Even if efficacy against infection is very high, rapid vaccine roll-out, high uptake, and continued NPIs for some weeks will be key to controlling the epidemic.”
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