The delta variant now accounts for more than 51% of all COVID-19 cases in the United States, according to the latest data from the Centers for Disease Control and Prevention.

As of last week, the strain accounted for about 20% of San Antonio’s positive COVID-19 tests, which followed national and state trends. It is estimated the delta variant now makes up almost half of all cases in Texas, UT Health San Antonio pediatrician Dr. Tess Barton told the San Antonio Report on Thursday. 

CDC officials are calling the delta variant “hypertransmissible” because it’s so easily spread among unvaccinated people. It’s also causing the local coronavirus positivity rate to rise again after it had been declining for months. San Antonio health experts say the best way to protect yourself and your family against the delta variant is to be vaccinated.

What is the delta variant and where did it come from?

The delta variant is a strain of COVID-19 that came from India in December, said University Health epidemiologist Dr. Jason Bowling. As an RNA virus — a virus that has genetic material encoded in ribonucleic acid — the virus jumps from host to host by invading the organism’s cells. 

All RNA viruses tend to develop mutations over time as they spread from person to person and “learn” from each host, Bowling said. Most of these mutations don’t change the virus in any way, but over time as the virus acquires different mutations, some of them may impact it, he said. 

“There are certain criteria that the CDC and World Health Organization use to determine if a variant is a valid concern, and the delta variant meets those criteria,” Bowling said. The three criteria ask if the mutation has changed the virus’ diagnostics, transmissibility, and/or its severity, he said. “The delta variant definitely is more transmissible.”

Five variants of the original virus are being watched by scientists, each with a Greek letter name. The alpha variant began causing concerns in the United Kingdom in September after scientists found it to be 40% to 50% more transmissible, Bowling said. When the delta variant emerged in December, it was found to be 50% more transmissible than the alpha variant. 

Currently, the delta variant has become the dominant strain globally and was the cause of the major surge in cases that India saw over the past several months. 

The variant was first confirmed in the U.S. last month.

Is the delta variant more dangerous than other strains? 

There is no evidence that the delta variant is any more dangerous than the original strain of COVID-19, Bowling said. However, it is definitely more transmissible — especially among unvaccinated people.

“It does seem to be about twice as contagious or transmissible as alpha, so it’s very easy to spread the strain from person to person,” Barton said. “So it’s not surprising that it’s sort of taken over very quickly.”

People who are fully vaccinated against COVID-19 appear to have a high rate of protection against all existing variants of the virus, Bowling said. The delta variant is mostly spreading among individuals who have not gotten vaccinated yet. 

“It is really important to get the full course to be fully vaccinated — to have the higher level of protection, even if you had prior infection,” Bowling said.

Who is spreading the delta variant?

Unvaccinated people, in general, are the ones spreading the delta variant, Bowling said. The majority of new cases is now among the 18- to 40-year-old age group, he said, although the majority of hospitalizations continue to be older unvaccinated individuals. 

The positivity rate among children has also increased as the delta variant circulates, Barton said. The rate of cases among children had been about 3% with the original strain of the virus last spring, but it’s increased to about 18% to 20% now, Barton said. 

Because children under 12 are not yet eligible to be vaccinated, family members around them should get vaccinated in order to “cocoon” them, Barton said. Protecting at-risk populations like children and those who cannot get vaccinated is yet another reason others should get vaccinated, Barton said. Once herd immunity is reached, it will limit the spread of the disease, she said.

I’m vaccinated. Will I be safe against the delta variant?

If you are vaccinated, you have a high degree of protection against the delta variant, Bowling said. While that doesn’t mean it’s impossible to get COVID-19, it makes it less likely and makes chances of hospitalization much lower, Bowling said. 

While the vaccine is not going to completely protect anyone against the delta variant or other strains, being vaccinated will make catching the disease and risk of death much lower, Bowling said.

“The good news that’s very reassuring is that the Pfizer vaccine is still 96% effective in preventing hospitalizations from COVID-19 disease when people are infected with a Delta variant,” Bowling said.

Those who’d only received one dose of the vaccine were only about 33% protected against COVID-19 and its strains, Barton said. She encouraged San Antonians to get both shots if they haven’t yet.

How can I help slow the variant’s spread?

If you’re not yet fully vaccinated, go get the jab — and make sure to get both doses of Pfizer or Moderna, say health experts.

“It’s not too late for people that [got the first dose] and then thought, ‘Well, I waited a while,’ or ‘I missed the window, it’s closed,’ — you can still get that second dose,” Bowling said. “Please go get the second dose.”

As of Thursday, almost 74% of Bexar County residents have received at least one dose of vaccine, while almost 60% are fully vaccinated. Scientists agree the herd immunity threshold is somewhere between 70% and 90% of people who have been either vaccinated or have antibodies from having had the coronavirus.

When will all children be able to get the vaccine?

Pfizer is doing a study on 5- to 11-year-olds, and anticipates those results will be available in September, Bowling said. Pfizer hopes to get rapid expansion to include vaccine eligibility for that group with the FDA shortly after the results are available, he said.

“September looks like the earliest timeframe we may see it, which that’s great because that’s right around when the school year starts,” Bowling said.

Lindsey Carnett

Lindsey Carnett is the general assignment reporter for the San Antonio Report.