Houston Chronicle Sunday
COVID HELP DESK: What is herd immunity, and how far until we get there?
Last week brought good news on the vaccination front, as a supersite opened in Houston and a one-shot vaccine inched closer to approval for emergency use. What does it all mean for herd immunity?
The Houston Chronicle’s COVID-19 Help Desk is here to answer your questions. Every week, a Chronicle reporter answers readers’ questions about how the virus works and what to expect with the vaccine.
Q: What is “herd immunity,” and why is there so much variation in when we’ll achieve it?
A: Herd immunity is the point at which a contagious disease begins to die out because enough people in a community are immune to it, whether because of vaccines or antibodies via natural exposure.
But there’s no definitive answer on the how much of the population this will require for COVID-19. Expert estimates have ranged from 50 to 80 percent, which Wesley Long, a Methodist Hospital infectious disease expert, said is due to the way the disease spreads, its ability to mutate into different strains and the rate of people who unknowingly develop antibodies because they were asymptomatic.
Experts are still researching the extent to which natural exposure to the virus can protect an infected person long term, he said.
“Some people will make a good immune response, some will make a longlasting response,” Long said. “Some people will make a mediocre-to-noimmune response or a very short-lived response to natural infection. And so there are a lot of unknowns.”
That’s why public health experts continue to stress the need for widespread vaccinations — including for those who’ve already had COVID — because vaccinations are tracked and give scientists a more concrete idea of how many people are still at risk.
Vaccines have also shown to be much more effective against the virus than natural infection, he said.
“Early on, people heard, ‘We need herd immunity, we need herd immunity,’ ” Long said. “And we do. But we want to get herd immunity safely, and the safe way to do that is through vaccination. Because when you get that, you don’t just get the benefits of natural immunity; you get immunity that looks as strong, if not stronger, than the best immune responses to natural infection without any of the risks of spreading that infection to other people.”
Q: How long will it take Harris County to reach a safe threshold for herd immunity?
A: As of last week, about 1 in 8 Harris County residents older than 16 have received at least one dose of the vaccine, according to a recent Chronicle analysis of state and local data. The number of people who’ve been fully vaccinated is about half that — 225,286 people, or about 5 percent of the county’s total population. So yes, reaching 50 to 80 percent is going to take a while.
But good news came last week: The state’s largest vaccine hub opened Wednesday at NRG Park, and officials believe the roughly 6,000 shots the facility plans to administer each day will ease the burden on smaller clinics that have been unable to keep up with demand since vaccines became available late last year.
And while experts estimated earlier this year that it would take until May or
June to vaccinate everyone in phase 1B, the addition of 42,000 shots a week being shipped to the county will significantly speed that process.
Also last week, federal regulators announced that the one-shot Johnson & Johnson vaccine is close to being authorized for emergency use. Local health experts have described the vaccine as a “game-changer” because it does not require multiple appointments. Nor does the new vaccine need to be stored at as low of temperatures as its two predecessors, which extends the time table before it goes bad.
The U.S. has a contract to purchase 100 million doses from Johnson & Johnson and an option to buy 300 million more, the Chronicle reported last week. If approved, the federal government will have ordered enough doses to immunize all 255 million adults in the U.S. by the summer.
Q: My child is highrisk. Does that make me eligible for a vaccine?
A: So far, Texas has not released guidelines on the parents of children who have pre-existing conditions. The Pfizer vaccine is currently approved for children older than 16, and the Moderna vaccine is approved for those older than 18.
Generally speaking, children have been shown to be less susceptible to COVID, according to the Centers for Disease Control and Prevention.
Q: Who is eligible for vaccinations at the new supersite at NRG Park? And how can I register?
A: The new site is the state’s largest vaccine hub and opened Wednesday with long lines that officials said have prompted them to tweak some operations there.
All told, they expect to inoculate about 6,000 people a day over the next two months.
City and county health officials are operating the site in conjunction with the Federal Emergency Management Agency and are following the state’s guidelines for vaccine eligibility, which prioritize people in the 1A or 1B categories.
That includes those 65 and older, front-line health care workers, residents of long-term care facilities and most people with underlying health conditions.
Priority is also being given to those living in the following high-risk ZIP codes: 77022, 77029, 77032, 77078, 77087, 77093, 77502, 77504, 77506, 77587, 77011, 77012, 77015, 77016, 77020, 77026, 77028, 77033, 77037, 77038, 77039, 77048, 77086, 77091, 77503, 77060, 77080, 77099, 77013, 77014, 77036, 77050, 77051, 77076 and 77090.
You can register through the city’s or county’s websites or by phone at 832927-8787.