British researchers warn it will take months before COVID-19 vaccination programs have impact on pandemic

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A group of researchers in Britain has warned that it will take months before mass vaccination programs have an impact in controlling the pandemic and that the threshold for herd immunity may never be reached because new variants of the virus are so contagious.

Their modelling concluded that even under the most optimistic scenario – rapid vaccine rollout and 85-per-cent uptake – it will be several months before the population comes close to the immunity threshold. They added that at least 80 per cent of the population will have to be vaccinated, given the new variants.

“Even with a very ambitious programme of three million doses per week, it will take 4-5 months to cover 80 per cent of the [U.K.] population with their first dose,” said the group’s study, which was released Thursday. “Under more pessimistic but plausible assumptions about vaccine coverage and efficacy, the population immunity threshold will never be reached. In that case novel coronavirus could become endemic.”

Vaccination “is a magic tool but it is not a magic bullet, in that its effect is not going to be instantaneous,” said Anne Cori, a lecturer in infectious-disease modelling at Imperial College London who worked on the modelling. “I think the impact of vaccination will only be seen once we manage to get very high coverage of the vaccine, and this depends on how fast we can roll it out but also how many people take it.”

Britain has been a world leader in rolling out a vaccination program, inoculating 4.6 million people as of Thursday. The government has set a target of 15 million by Feb. 15, which includes hospital staff, long-term care home residents and everyone over the age of 70. Officials also hope to have everyone over the age of 50 vaccinated by late March.

The scientists said those targets will provide minimal overall protection and warned against easing lockdown restrictions before May at the earliest. Doing so would send the rate of infections and hospitalizations soaring, they added. “I would be worried about any early opening of any bars and restaurants or just reducing the controls,” said Matt Keeling, a professor of populations and disease at the University of Warwick who also worked on the study.

One of the main concerns with the vaccines currently in widespread use – from Pfizer-BioNTech, Oxford-AstraZeneca and Moderna – is whether they protect against the spread of infection. A vaccinated person might not get sick, but they could still be contagious.

“I think people need to realize that the efficacy measures at the moment are not 100 per cent and also that they are not measures of efficacy against infection,” Dr. Cori said. “So even if someone is vaccinated, if they go to a bar, they might be a vector of transmission as far as we know.” She added that several studies were under way to determine the transmission-blocking capabilities of the vaccines, but the result won’t be known for several months.

Mark Woolhouse, a professor of infectious-disease epidemiology at the University of Edinburgh, said even if the vaccines prove to be 90-per-cent effective in preventing disease, the herd immunity threshold still might not be achievable, particularly given the appearance of the British variant of the virus, which has proven to be as much as 70 per cent more contagious. The threshold is met when the reproduction number, or R, falls below one, which means the virus is no longer spreading exponentially.

“When you get up to high levels of efficacy, the emphasis shifts from the performance of the vaccine to the coverage you’ve achieved in the uptake,” he said. “There are very few vaccines anywhere in the world where people get above 90- or 95-per-cent coverage. And if there are 5 per cent or 10 per cent of the most vulnerable people unprotected, there is clearly a public-health hazard there.”

Another study released Thursday by two scientists at the University of East Anglia also concluded that achieving herd immunity will be difficult with the current vaccines. “Vaccinating the entire population with the Oxford vaccine would only reduce the R value to 1.325 while the Pfizer vaccine would require 82 per cent of the population to be vaccinated to control the spread of the new variant,” the study concluded. “The possibility of transmission from vaccinated but infected individuals to vulnerable unvaccinated individuals is of serious concern.”