Coronavirus vaccines block disease, but do they protect people from getting infected?

If vaccines being rolled out around the world ward off not only symptoms but the virus itself, it could and hasten the return to normality

But the ‘big concern is that the vaccines prevent illness, hospitalisation and death, but won’t sufficiently prevent transmission’, expert says

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If coronavirus vaccines can ward off not only symptoms but also the pathogen itself, it could hasten the world’s return to normality. Photo: AFP

Published: 10:15pm, 25 Feb 2021Updated: 1:46am, 26 Feb 2021

As reports this week from Scotland and Israel – where much or most of the population have had Covid-19 jabs – confirm that vaccines largely prevent people from getting sick, another question is emerging: do they also block infection?

A lot depends on the answer, experts say.

If vaccines being rolled out worldwide ward off not only symptoms but the virus itself, it could sharply slow the pathogen’s spread and hasten the return to normality.

“If the true impact on infections was very high, it would be great news because that is what we need for herd immunity,” said Marc Lipsitch, director of the Centre for Communicable Disease Dynamics at the Harvard T.H. Chan School of Public Health.

Herd immunity is achieved when most of a population – estimates vary between 60 to 80 per cent – have acquired defences against a virus, whether through vaccination or because they caught the bug and survived.

But if the Pfizer, Moderna and AstraZeneca vaccines – and perhaps others made in China, Russia and India – shield poorly against infection, then even people who have rolled up their sleeves to be injected remain potential, unwitting carriers.