How many people need to be vaccinated to get back to normal?

Herd immunity percentage is not a ‘magic threshold’

Margaret Keenan
Margaret Keenan was the first patient in the UK to receive the Pfizer/BioNtech vaccine
(Image credit: Jacob King/Pool/Getty Images)

The UK has taken another tentative step out of lockdown, with the return of indoor socialising at home and in pubs and restaurants.

The blanket travel ban has been lifted, and theatres, sports stadiums and cinemas can reopen, in what has been billed as the penultimate stage before all restrictions are removed on 21 June.

However, the prime minister has warned that the race between the virus and the country’s vaccination rollout could become “a great deal tighter” with the emergence of the Indian Covid-19 variant.

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How many vaccines so far?

The UK administered 56.7 million jabs up to 16 May, according to the website. First doses have been given to 36.6 million people, while 20.1 million have also had a second shot.

Oxford University researchers calculate that this amounts to nearly 30% of people in the country having full protection, while nearly 54% have partial protection, the highest national proportion in the world apart from Israel.

How many people need the jab?

Johnson’s roadmap for ending the UK’s third lockdown is contingent on the vaccine rollout continuing at pace. Ahead of each step in the lockdown-easing plan, ministers have been weighing up the vaccine rate and its effectiveness in reducing hospitalisations and deaths, against the risks of infection rates and new variants.

The government has said all adults, which make up about 80% of the population, will be offered a vaccination by the end of July. However, not all adults are able or willing to have the shot.

“To go back to a pre-pandemic lifestyle, we would need at least 70% of the population to be immune to keep the rate of infection down (‘achieve herd immunity’) without restrictions on activities,” say Gypsyamber D’Souza and David Dowdy, epidemiologists at Johns Hopkins Bloomberg School of Public Health.

But they say that the herd immunity percentage is not a “magic threshold”, as both viral evolution and changes in human interaction can affect the number.

With an “amazingly successful” vaccination drive, and cases, hospitalisations and deaths down, there is a “window of opportunity to eliminate the virus in the UK, or at least to bring it to near extinction, and to concentrate on controlling isolated outbreaks”, says Adam Kleczkowski, professor of mathematics and statistics at the University of Strathclyde, writing for The Conversation.

However, he notes that the herd immunity threshold for new variants is “probably higher” than 70% and that, as vaccinations are not 100% effective, a higher proportion of the country will need to be treated. If unvaccinated people are concentrated in the same area, there is also a risk of pockets becoming “a breeding ground for super-spreading events”, says Kleczkowski.

“Globally, extremely uneven vaccination rates pose another hurdle to herd immunity,” writes Joshua Cohen in Forbes. As each successive wave proves, “the virus is highly transmissible and frequently generates new variants of concern”, says Cohen, and this has “important implications for public health policy in countries that are presently ahead in the vaccination race”.

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