Researchers have warned that early relaxation of coronavirus disease 2019 (COVID-19) control measures in the UK could lead to pronounced waves of further infection with the causative agent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
The team’s mathematical model showed that even when phase 1 of the current vaccination program has been completed, strict non-pharmaceutical interventions (NPIs) will still be needed to prevent a large wave of infection if herd immunity has not been established.
While the novel vaccines against SARS-CoV-2 provide a potential solution to combatting the COVID-19 outbreak, this is highly dependent on the vaccine’s ability to block transmission and its level of uptake among the population. These factors need to be carefully monitored as vaccination programs are rolled out across the UK and other countries, warn the researchers.
Matt Keeling and colleagues from the University of Warwick found that even relaxing NPIs gradually over a period of many months would not prevent the worst effects.
A pre-print version of the paper is available on the medRxiv* server, while the article undergoes peer review.
This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources
First and second waves in the UK
In the UK, the first cases of SARS-CoV-2 were identified on 31st January 2020, with an exponential rise in cases observed through February and March.
The government introduced the first national lockdown on 23rd March, which led to a decline in the infection rate that continued until August. A subsequent relaxation of control measures led to social interaction and mixing that precipitated a second wave and, eventually, a second lockdown in November.
By early December, the UK had seen more than 60,000 deaths and around 225,000 hospital admissions as a result of COVID-19.
Mass vaccination of the population against SARS-CoV-2 represents a potentially rapid exit strategy.
In early December 2020, one of the world’s first vaccines developed against coronavirus (Pfizer/BioNTech’s BNT162b2[6]) was approved for use in the UK, with several others showing promising results in late Phase 3 trials.
By the 12th December 2020, the UK had ordered 357 million doses of vaccines from seven different developers.
Predicted daily deaths in the UK following the start of an immunisation program and relaxation or removal of NPIs. Panels (a) and (b) show the effect of relaxing current NPI measures down to those seen in early September 2020 (R 1.2 − 1.4) from January or April 2021 respectively. Panel (c) displays the aggregate effects of partial release of NPI measures at different dates during the vaccination program (left) compared with complete release from July 2021 (right); the upper limit, central bar and lower limit of each box corresponds to pessimistic, default and optimistic assumptions about vaccine uptake. The lower panels (d) and (e) correspond to a gradual reduction in NPIs until all controls are removed, as illustrated by the grey area. The default scenario (a,b, d & e) assumes 75% uptake in the general population; the optimistic scenario has an increased uptake at 85% in those above 50; while the pessimistic scenario has a decreased 65% uptake in the over 50’s and 45% uptake in the remaining population.
The dynamics of vaccination against SARS-CoV-2 are complex
“Normally, relatively simple relationships between epidemiological parameters, vaccine efficacy and vaccine uptake predict the success of any immunization program,” says Keeling and colleagues.
“However, the dynamics of vaccination against SARS-CoV-2 is made more complex by age-dependent factors, changing levels of infection and the potential relaxation of non-pharmaceutical interventions (NPIs) as the perceived risk declines.”
In particular, one factor that remains unknown is the degree to which the novel SARS-CoV-2 vaccines prevent onward transmission.
What did the researchers do?
The team used an age-structured mathematical model matched to a range of epidemiological data to predict the dynamics of COVID-19 into 2021 and beyond, based on various combinations of scenarios. The model forecasts the likely number of deaths and hospitalizations, therefore providing important insights into the interaction between the UK vaccination program and future relaxation or removal of NPIs.
Unsurprisingly, the team found that the largest waves of infection and the highest number of deaths occurred in the absence of vaccination.
With modest relaxation of NPIs (to the early September 2020 level) at the start of 2021, subsequent waves of infection occurred, even under the most efficacious assumptions (a vaccine that blocks 75% of infection).
The model estimated that more than 10,000 deaths would occur due to the slow decline in cases from the current high level of infection.
It also predicted that if all NPIs were completely lifted once both phases of the vaccination program were complete, a substantial outbreak and a large number of associated deaths would occur.
When a vaccine that does not block transmission was considered, the removal of NPIs triggered an uncontrolled wave of infection that could only be escaped by individuals who had been successfully immunized.
The team says that even under optimistic assumptions for both vaccine and uptake, the removal of NPIs could result in 49,000 deaths, with 13,000 occurring between January and July and 36,000 from July onwards.
A slow relaxation of NPIs generated the lowest number of deaths, which, under the most optimistic assumptions was still estimated to be around 39,000.
What are the study implications?
The team says the study suggests that relaxing NPIs before sufficient herd immunity has been established could precipitate a large wave of infection, hospitalizations, and deaths.
Even with high vaccine uptake levels, a substantial fraction of the population will need to be immunized to prevent future waves of infection. Strong NPIs will also still be needed, even when phase 1 of the vaccination program is complete.
“While the novel vaccines against SARS-CoV-2 offer a potential exit strategy for this outbreak, this is highly contingent on the transmission-blocking action of the vaccine and the population uptake, both of which need to be carefully monitored as vaccine programs are rolled out in the UK and other countries,” concludes Keeling and colleagues.
This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources
Article Revisions
- Apr 3 2023 - The preprint preliminary research paper that this article was based upon was accepted for publication in a peer-reviewed Scientific Journal. This article was edited accordingly to include a link to the final peer-reviewed paper, now shown in the sources section.
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