Revealed: How More Contagious Covid Variants Spread

Why are some coronavirus variants more transmissible than others? We asked the experts.
OLI SCARFF via Getty Images

Every week, we’ll answer your questions on Covid-19 and health in a feature published online. You can submit a question here.

HuffPost UK reader Tara asked: “How do the highly contagious variants spread?”

Cases of the B1617.2 variant, which originated in India, have risen once more with 3,434 cases in England – up from 2,111 cases the week before.

The variant is predominantly affecting the north west of England – particularly Bolton – as well as London, but “clusters of cases” are also appearing across the country, Public Health England (PHE) said.

There’s evidence the variant of concern is growing rapidly and may be even more transmissible than B117, or the so-called ‘Kent variant’, that is currently dominant in the UK. So, what makes a variant like this more transmissible?

Viruses multiply by copying themselves over and over, but these copies can alter slightly as they go along – becoming a new variant.

Most of the time, these variants don’t alter much about the way the virus works. However, sometimes they can alter factors such as how quickly the virus spreads, whether it can evade the body’s immune response more effectively, or even the severity of the disease it causes.

When this happens, a variant will go from one that’s simply being monitored (also known as a variant under investigation) to one of concern – and that requires action to reduce its spread.

In the case of B1617.2, surge testing is being carried out in areas affected, as well as enhanced contact tracing and vaccines. Wastewater is also being monitored to identify early warning signals of where the variant may be present throughout the UK. The rise in cases coincides with lockdown easing, as people are now allowed to meet indoors.

With these newer, more transmissible variants, the ease in which they spread is thought to be down to changes in the spike protein – the multiple stalks that stick out of the virus. This protein is the part of the virus that first attaches to a human cell in the body, so it’s pretty important for transmissibility.

Professor Lawrence Young, a virologist from Warwick Medical School, tells HuffPost UK: “The spike protein [brings about] infection by binding to the surface of the cells in our bodies, and then these changes [or mutations] make the virus more sticky so it can more easily infect.

“Some of these changes [to the spike protein] also make the virus grow better in our cells and therefore produce more infectious virus. So, the increased transmissibility is a combination of the variants being more efficient at infecting cells and being able to replicate more in our cells, producing more virus to infect other people.”

A mutation in the spike protein – called N501Y – has been detected in the B117, B1351 (which originated in South Africa) and P1 (from Brazil) variants. This mutation in particular has been associated with increased transmissibility.

Evidence suggests B1617.2 is now “outcompeting” other variants, including B117, according to Professor Sharon Peacock, executive director and chair of COG-UK (the Covid-19 Genomics UK Consortium).

It’s likely that, over time, B1617.2 will go on to replace B117 in England – in the same way that B117 replaced other variants at the end of last year.

Scientists are confident the new variant has increasing growth over B117, “with a current estimate that B1617.2 has a transmission advantage of more than 50% over B117,” Prof Peacock explained. This means it’s looking likely it’s more transmissible than the Kent variant – although research into this is ongoing.

There’s no evidence the vaccines won’t work against this new variant. A new report from PHE published on May 22 suggests the Pfizer coronavirus vaccine is 88% effective and the AstraZeneca jab is 60% effective against the new variant after two doses. Both vaccines were just 33% effective three weeks after the first dose, however.

“Vaccines have worked against all other variants to date and assuming this is the case for B1617.2, we could anticipate a reduction in the number of infection cases compared with what would happen in an unvaccinated population,” said Prof Peacock, “and a reduction in disease severity, including the most severe infections that require hospital admission and could result in death.”

“Vaccines have worked against all other variants to date.”

- Professor Sharon Peacock, executive director and chair of COG-UK (the Covid-19 Genomics UK Consortium)

In the meantime, experts are paying close attention to hospital admissions with Covid-19, which remain low, and the proportion of mild versus severe cases.

Because all variants infect in the same way, predominantly via air droplets and aerosols, measures used to reduce virus spread will still help stop these newer variants spreading, says Prof Young. So that means social distancing, wearing face masks, reducing close contact and improving ventilation in indoor settings.

PHE says the best way to halt the spread of any variant is to test regularly using lateral flow tests or using PCR tests if you have symptoms, and isolate if you or someone in your household tests positive or if you’ve returned from an amber or red list country. People are still urged to continue to work from home where possible.

Experts are still learning about Covid-19. The information in this story is what was known or available at the time of publication, but guidance could change as scientists discover more about the virus. To keep up to date with health advice and cases in your area, visit and