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Healthcare providers in the United States are pushing to vaccinate more than 70% of eligible Americans to get closer to herd immunity against the novel coronavirus.
Some disease experts believe that achieving true herd immunity, a state in which COVID-19 transmission between individuals isn't likely, won't occur anytime soon.
Achieving herd immunity may be increasingly difficult due to new COVID-19 variants and a dip in vaccination rates, as well as uncertainty over how long immunity will last.
With more than 37% of the United States' total population entirely vaccinated against COVID-19, Americans may be wondering if their communities are nearing herd immunity. The term has been tossed around by health experts and local leaders for more than a year, used in estimations for ending lockdown restrictions and strict social distancing last summer. It's been an evasive goal for nearly all nations across the globe, and here in the United States, mounting evidence suggests that most states won't be able to position themselves as majorly immune anytime soon. Mostly, a dip in vaccination rates and an increase of cases tied to developing COVID-19 variants pose a threat to herd immunity on a global scale, not just at the national level.
It's not all bad news — President Biden recently announced his federal administration has a new goal of having at least 70% of eligible American adults (and children!) receive at least one vaccine dose by the Fourth of July. An added goal tied to the announcement was fully inoculating 160 million adults by Independence Day, as NPR reports, in the interest of rolling back more public health restrictions across the nation to stimulate local economies and, hopefully, bring back a greater sense of normalcy in time for summer.
This plan, and herd immunity itself, all hinges on whether or not Americans continue to turn out to vaccine clinics, explains Nelson Michael, M.D., the director of Walter Reed Army Institute of Research's Center for Infectious Disease Research. "It's a race right now to get people vaccinated, to stay ahead of the curve, and also to stay ahead of these variances that are emerging," he adds.
Read on to learn more about herd immunity and why some experts think progress is coming, even if true herd immunity isn't ever achieved.
What is COVID-19 herd immunity?
At its core, herd immunity against COVID-19 will occur when a majority of the U.S. population — referred to as the "herd" in this case, Dr. Michael explains — becomes immune. It's a theoretical step in turning baseline coronavirus illnesses endemic rather than a raging pandemic across borders; if herd immunity is achieved, it means that the spread of disease will slow between individuals, even if someone hasn't received or earned immunity just yet.
Dr. Michael compares herd immunity to protections afforded by helmets and seatbelts: "What we're doing right now is that the more people that are wearing helmets or seatbelts — or, in this case, becoming vaccinated — the more protected you are if someone hits you."
After someone is infected with SARS-CoV-2 (the virus that leads to a COVID-19 infection) they earn some immunity against falling ill once more. But earning immunity this way puts a huge strain on our healthcare resources, as we saw in most of 2020 and even now, in states where infection rates are high. Health experts are pushing Americans to earn their immunity through vaccinations, which can provide more promising immunity than natural infection, as doctors have well established by now that you can indeed get COVID-19 twice.
For nearly all Americans, this is the first pandemic they've ever lived through — but communities have historically achieved herd immunity through vaccination before now. Outbreaks of smallpox, polio, rubella and other potentially deadly diseases have been quelled by vaccines in the past, Dr. Michael explains. And while the vaccine developed to fight COVID-19 is brand new, he adds that there's enough data to know that this vaccine can (at minimum) prevent too much strain on our healthcare system: "It's very clear that current vaccines prevent you from becoming either hospitalized or dying… In the real world, not just within clinical trial data, you see [vaccines] prevent COVID sicknesses from becoming life-ending events."
When is herd immunity completely attained?
In other words, how many people in the U.S. need to have some sort of immunity against the disease to be considered a true herd? It's a complex question and requires health experts to constantly pull data on current infections.
Analysts at the Mayo Clinic explain that the U.S.'s threshold proportion — the percentage of the general public that's susceptible to getting sick and spreading COVID-19 around — must be lower than the percentage of people who are immune to the disease. Only then will the nation reach a true herd immunity status.
How many people is that really, though? "I can tell you that I don't think anyone really knows exactly what that number is. We know it needs to be high," Dr. Michael explains.
The fact that COVID-19 is highly contagious is likely driving President Biden's goal for 70% of eligible Americans to be vaccinated by early July. Because the disease has spread easily and may continue to do so, it will be hard to get the threshold proportion of the public down below immune portions. Mayo Clinic experts add that, as a general rule, it's estimated that "94% of the population must be immune to interrupt the chain of transmission."
It's all made more complex and complicated by new COVID-19 variants that pose some threat to vaccinated individuals. Like earned immunity after getting sick, the immune response that comes with a COVID-19 vaccine likely doesn't last forever, nor does it provide as much protection against new variants compared to traditional strains of the disease that spread in 2020. It's why most vaccine manufacturers are currently working on additional booster shots right now.
What percent of Americans have been fully vaccinated at this point?
At this time, more than 275 million doses of vaccines created in part by teams at Pfizer, Moderna and Johnson & Johnson have been administered to around 124 million people. Data shows that this amount is just over 37% of the U.S. population.
The rate of vaccinations is slowing compared to early 2021, however. Data analysts at the New York Times have published a live graph demonstrating that supply is currently exceeding demand. The average number of individuals getting their first dose (or a single-dose shot) on any given day has fallen by half since April 13, the Times reports. They add that CDC data reveals that the decline in vaccinations is highest in adults aged 18 to 64, and as of early May, over 50% of this demographic remain unvaccinated despite expanding eligibility.
Whether it's due to hesitancy over potential side effects or lack of resources to reach clinics or pharmacies, the dip in demand for a vaccine could make reaching herd immunity much more difficult. It's also coupled with the fact that vaccine rates worldwide are far from being close to vaccine rates in the United States, but borders and travel remain mostly open.
"We want to make sure we protect ourselves not just across the U.S., but as a global community — if people overseas are not protected, the virus will keep making its rounds," says Dr. Michael, who cites current outbreaks in India as a "fire" that could easily spread elsewhere. "There are examples of how vaccines can help us, the best one being smallpox, which is a disease we've not only eradicated at home but across the world. We're also getting close to doing the same for polio."
How much longer until we reach herd immunity here in the United States?
For most experts, it's too early to answer this question — and some may believe that total herd immunity is simply unattainable. Ultimately, current vaccinations provide protection against severe side effects or deadly consequences, allowing Americans to live alongside the spread of COVID-19 for now.
Monitoring progress against President Biden's July goal may be the best timeline to expect benefits that are as close to herd immunity as we've ever been, Dr. Michael says. "Experts in epidemiology had data from other respiratory infections that suggest when you reach that level of immunity by vaccination, 70% in this case, that the infection curves begin to collapse," he explains, adding that new infections in the U.S. are at low points now compared to earlier 2021 and all of 2020.
"The country is increasingly becoming vaccinated and I think if we get to the fall season, and numbers continue to plummet — without rising trends due to variants or the reemergence of the cold weather or relaxation — I don't want to say we're going to be back to normal, but we'll be closing in on that more than ever before," he adds.
While vaccines afford you many protections, it's important to still embrace best practices for staying safe and lowering COVID-19 risks, as Dr. Michael shares that 2% of infected individuals end up with extending complications stemming from the disease. "It doesn't have a rate of death similar to a disease like Ebola might have… but there's a segment of our society, especially people of color, Black, Latino, indigenous American and indigenous Alaskan individuals, who have a higher risk of becoming infected and having long COVID symptoms if they're infected. The data is very clear on this, and should be motivation for people to avoid risk."
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