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Waco's path to herd immunity uncertain as vaccination improves COVID-19 outcomes

Waco's path to herd immunity uncertain as vaccination improves COVID-19 outcomes


When Dr. Jackson Griggs of Waco Family Medicine thinks of the end game for the COVID-19 pandemic, he envisions a series of paving stones, with the virus hopping from stone to stone as it moves from person to person.

The more people get vaccinated, the fewer paths the virus has, and it begins to vanish from the human population. At some point, even those who can’t or won’t get the vaccine are protected by the “herd” of people around them.

“Without people, these germs largely disappear,” said Griggs, the president and CEO of the nonprofit clinic system that serves 60,000 people a year.

That is the meaning of “herd immunity,” a widely discussed but often misunderstood goal as Texas prepares to open vaccinations to all adults Monday. Experts define the threshold as anywhere from 60% to 85% of a population that is immune to the virus.

Even by the the most optimistic definition, local epidemiologists and public health officials agree that McLennan County is nowhere near herd immunity. As of Friday, 30,114 residents had been fully vaccinated. That amounts to about 15% of McLennan County’s 16-and-up population or about 12% of the total population, meaning 150,000 more residents need to get vaccinated to get to the 70% threshold.

Dr. Vaidehi Shah, senior epidemiologist for the Waco-McLennan County Public Health District said while there’s light at the end of the tunnel it’s still far too soon for anyone in Central Texas to safely gather in groups or stop wearing masks. She said it’s far too early for the small number of vaccinations to have a real effect on the local case count, which stood at 180 active cases and 25,991 total as of Friday. On the heels of spring break weeks, nationwide case counts have again been increasing.

“I can say the vaccination effort is helping us in reducing the severity of the disease,” Shah said. “But when it comes to the number of cases it’s too soon for us to see that effect.”

Griggs said he estimates McLennan County could reach herd immunity by late 2021 or 2022, but that won’t be the finish line for defeating COVID-19.

“Herd immunity is not synonymous with ‘When we can all return back to normal,’ not exactly synonymous,” Griggs said. “There are some epidemiologists that argue we will never reach true herd immunity with this particular virus.”

Almost 3.6 million Texans, about 12% of the population, were fully vaccinated as of Saturday. About 15% of the population nationwide is filly vaccinated, according to the Centers for Disease Control and Prevention.

Texas Department of State Health Services reported more than 3.3 million Texans have been fully vaccinated against the virus, about 11% of the total population as of Saturday. About 14% of the country’s total population has been fully vaccinated, according to the U.S. Centers for Disease Control.

Shah said she expects fatalities and hospitalizations to remain lower going forward because health care workers, elderly people and people with medical conditions were prioritized in the vaccine rollout. Still, the virus could spread quickly among those who still haven’t been vaccinated even as overall deaths and hospitalizations fall.

Dr. Matt Pattillo, a pulmonologist at Ascension Providence Medical Center, said the past several weeks of work have seen improvement compared to just a few months ago. At one point, the hospital had 110 COVID-19 patients and was seeing deaths daily for weeks on end.

“You just, you couldn’t, you couldn’t do a good enough job and so you constantly felt as if you weren’t adequate,” Pattillo said.

As of Friday, Waco’s two hospitals had a combined 31 COVID-19 patients.

“Certainly things are much, much better,” Pattillo said. “What’s it going to look like in a couple of months? I don’t think anybody truly knows.”

The lifting of Texas’ statewide mask mandate and concern over virus variants represent complicating factors. It remains to be seen how effective existing vaccines are against the virus variants that have started to circulate more widely.

“Given that they’re much more prevalent now in circulation, we wear the mask, protect ourselves and others from these variants, because we don’t know for sure if that vaccine is going to protect us from these variants,” Pattillo said.

Shah said that how the virus continues to mutate also will have long-term implications. It is very possible it could become an endemic virus like flu or the common cold, and data gathered by public health workers in the coming months will provide a clearer picture of whether that is likely.

“We know that coronaviruses do mutate a lot,” Shah said. “We may have an annual vaccine, like the flu vaccine, or we may not have an annual vaccine. … It would all depend on how the virus mutates.”

She said the rapidly opening vaccine eligibility in most of the country is encouraging, but she is concerned younger people may not be as eager to accept the vaccine as those who were most at risk.

“We’re hoping the numbers will increase. We should only go higher and higher moving forward,” Shah said. “But it would depend a lot on public perception of the vaccine.”

Shah said the health district just aims to vaccinate as many people as possible rather than focus on a specific target number of vaccinations.

Griggs said the threshold of “true” herd immunity, the point the virus completely disappears from the population, is more of a concept than a tangible goal. If we ever reach it, he said, it would only be in the distant future.

“There is a lot of value in talking about herd immunity because it represents this concept that enough people are vaccinated that the virus is not spreading among us… very much,” Griggs said, pausing. “That ‘very much’ is really what hinges on the difference between true herd immunity and what people are interested in.”

Emily Smith, an epidemiology professor at Baylor University and author of the “Friendly Neighbor Epidemiologist” page on Facebook, said variants that are more transmissible than other strains of the virus make answering the question of herd immunity even more difficult.

“Without the variants, if we hit 50% we’ll see something,” Smith said. “With the variants … I don’t know if that’s going to complicate factors and keep us in a perpetual race.”

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