'COVID is not done with us': Why is the BA.5 COVID-19 variant so contagious?

ByMaggie Green KTRK logo
Wednesday, July 13, 2022
Health officials urgeCOVID  booster shots as BA.5 variant spreads
The virus has evolved into a strain that is highly transmissible BA.5, that can sidestep immunity from previous Omicron infections and vaccinations, health officials say.

DURHAM, N.C. -- The COVID-19 pandemic is far from over, according to experts.

Even though cities and states are loosening mask requirements and allowing their emergency declarations to expire, the United States is in an unmistakable surge of COVID-19 cases.

The rapid rise in cases is due largely to the evolution of a new subvariant of Omicron called BA.5.

Dr. David Wohl, a professor of medicine and infectious disease at University of North Carolina at Chapel Hill, explained how a variant like BA.5 arises.

Dr. David Wohl, a professor of medicine and infectious disease at University of North Carolina at Chapel Hill, explained how a variant like BA.5 arises.

"Unlike people, viruses make sloppy copies of themselves, so the baby virus often looks very different and it's often defective," Wohl said."So mutants happen all the time, and most of those mutants don't do anything, but once in a while a mutant comes along that's better than the other viruses-better in some way that helps it survive, better in being transmissible from one person to another."

Wohl added that because viruses are making billions of copies of themselves, the likelihood of a more advantageous mutant is higher and the evolutionary process is sped up.

BA.5 is the most prevalent variant in the United States, rising from 17% of cases in the country a month ago to 65% last week, according to Centers for Disease Control and Prevention data. This variant spreads much more quickly than previous variants, according to a news article from the science publication Nature, infecting more people at a given time.

The number of people an infected person can transmit the virus to is called the R0 (R-naught) value. Early COVID-circulating in the spring and summer of 2020-had an R0 of about 2-3, meaning every infected person could pass the virus to two or three others. The first couple strains of Omicron, largely responsible for the peak surge of cases last winter, had an R0 of 8-9, according to Dr. Wohl, meaning the rate of infection was exponentially higher.

BA.5 is even more transmissible, and better at evading the forces of the immune system. Even those who were previously infected or received vaccinations and boosters are testing positive for the virus. Dr. David Montefiori, a virologist at Duke University, says that's because those who had a mild infection previously don't create a strong immune response to the virus.

"A lot of people-almost half the people who get infected with this virus-when they recover they don't have a very strong immune response; their body is just able to eliminate the virus without having to mount a strong immune response against it," Montefiori said. "It's good to get vaccinated, because you don't have that range of differences in immunity with the vaccine. Most people do mount a good immune response to the vaccine, unlike what we see in people who recover from infection."

While some experts claim the R0 of BA.5 is as high or higher than measles-widely considered the most contagious virus with the highest known R0 value of 18-Wohl said that's simplifying the situation because R0 assumes a completely susceptible population, and many people have some degree of immunity at this point in the pandemic.

"R0 assumes that the population is susceptible," Wohl said. "There's a lot of people who are not susceptible completely to getting infected with BA.5 because they've been vaccinated and especially boosted, or they've been infected with another variant that provides some protection. Maybe not as good as we'd like, but some protection. So again, there's a wall that the virus has to jump over in order to infect enough people. So R0 is not 18 right now, it's lower, but it's pretty high, and we see that, especially now that fewer and fewer people are taking measures not to infect other people or get infected."

Though a letter in the New England Journal of Medicine suggested that the initial vaccine plus a booster is more than 20 times less effective against BA.5 omicron, Montefiori said getting vaccinated now is vital, especially for those who have yet to get their initial doses or a booster.

That's because the vaccine triggers two branches of the immune system. First, the vaccine causes a type of immune cell known as a B-cell to produce antibodies-little torpedoes that fire against the virus, and more specifically against the proteins that allow the virus to enter cells, blocking them from working. However, those antibodies wane over time.

But another type of immune cells known as T-cells don't disappear. These are fighter cells that gobble up viruses like SARS-CoV-2-the virus that causes COVID-19-and other invaders in the body.

"These killer cells are now working together with the antibodies and combined, they're able to control the virus and eliminate it from the body before you get seriously ill," Montefiori said.

Wohl added that thinking about vaccines in terms of absolute protection or none at all is a mistake.

"They do protect you from infection," Wohl said. "It's not as good as it used to be for previous variants, but for BA.5, your booster will protect you. It won't be 100%, but you'd rather have some armor, even if it's chinky armor, than no armor."

Montefiori said the pandemic isn't over-COVID will be something we live with for a very long time.

"Maybe forever," Montefiori said. "We're periodically going to see it evolve and there are going to be spikes."

And both experts said two simple actions can reduce a person's individual risk of getting very sick or spreading disease to someone else vulnerable.

First, both said wearing a mask indoors protects against infection, especially for those elderly or immunocompromised.

"It's a barrier method and lots of people are into barrier methods for lots of different infectious diseases," Wohl said. "This is a barrier method for preventing COVID-19 spread and acquisition."

Wohl and Montefiori also recommended that anyone over the age of 50 get a second booster shot if they haven't done so yet.

"If you haven't had a shot since January 1, it's time for a shot," Wohl said. "There's no downside, only positive."

Both added that a booster shot specific to BA.5 is expected by the fall and would be safe for anyone to take even if they get another booster now.

"The hope is that that will not only provide better efficacy against BA.5, but hopefully also against future variants," Montefiori said. "We're now starting to put these other variants into the vaccine that have mutations in them that are contributing to the virus's escape from immunity. The immune system will now recognize those forms of the virus and attack it."

In the meantime, both experts said to keep washing hands and wearing a mask.

"We might feel we're done with COVID," Wohl said. "But COVID is not done with us."