What makes the UK coronavirus strain more contagious?

Coronavirus test
Posted at 2:34 PM, Jan 11, 2021

SAN DIEGO — A small, preliminary study by Pfizer suggests its vaccine is still effective against the more contagious strain of coronavirus first detected in the United Kingdom.

The study analyzed the blood of 20 vaccinated patients in lab dishes and found their antibodies still neutralized one particularly troublesome mutation in the virus’ spike protein.

The results have not been validated yet by outside experts. Tests of other leading vaccines are still ongoing. There have been several dozen cases of the UK strain detected in California so far, in addition to locations in Colorado and New York.

The UK strain is officially called B.1.1.7. It came to the attention of scientists last month after they noticed an outbreak in England’s Kent County spreading faster than usual.

After reviewing viral samples collected from patients, scientists realized the first known case of B.1.1.7 emerged in late September.

The strain has 17 mutations within its proteins, including eight changes to the critical spike protein that allows the virus to latch on and enter cells.

The mutations in the spike protein make it stickier to our cells, UC San Francisco infectious disease expert Dr. Peter Chin-Hong said, particularly a mutation called N501Y that was the focus of the Pfizer study.

“I tell people it's like Velcro. This particular COVID variant will just stick more to the surface of my nose or mouth,” Chin-Hong said.

The stickier spike protein is a major reason the UK variant seems to be at least 56% more contagious, he said, although there’s no sign yet it’s more deadly.

Another one of the mutations within the spike protein, P681H, may also allow the strain to linger closer to the nose and throat of an infected person, rather than deep inside their lungs.

“It's possible that it's more transmissible because it essentially grows better in the upper respiratory tract,” said Dr. Shane Crotty of the La Jolla Institute for Immunology. With more virus in the upper respiratory tract, more particles can escape when an infected person speaks or coughs, he explained.

Viruses mutate all the time when they make tiny mistakes while copying themselves. Most viral genomes sequenced today have about 20 differences from the first cases in China in January. The virus acquires one to two mutations per month on average; the majority of those changes are insignificant.

But scientists say seeing a variant with 17 mutations pop up at once is very unusual.

Experts believe the UK strain likely emerged in a patient with a compromised immune system. Patients with weaker immune systems experience longer battles with the virus, sometimes lasting a few months.

The longer the virus survives within someone, the more copies it generates, and the greater the likelihood of genetic mistakes.

“At one point, one of these [replications] is going to result in an error. And then at some point one of these is going to increase the survival of the virus,” Dr. Chin-Hong said.

However, many experts have expected for some time that the authorized COVID-19 vaccines would still offer significant protection against the UK variant. That’s because when it comes to antibodies and T-cells, the immune system doesn’t put all its eggs in one basket.

“The immune system is making a range of antibody responses and a range of different responses that are recognizing overlapping regions” on the virus, Dr. Crotty said.

Dr. Chin-Hong said the body’s immune strategy is kind of like a firing squad with 1000 guns. If a virus mutates, a single mutation might evade one of the guns, but “you still have 999 left.”

This story originally reported by Derek Staahl on