The U.S. has surpassed 46 million confirmed cases of COVID-19, the disease caused by the novel coronavirus, and natural immunity from a prior infection may not be enough to rely on when considering the ultimate aim of reducing hospitalization and death caused by transmission — especially when it comes to mitigating the threat to the most vulnerable among us.

"The problem with natural immunity is that A) it's not as good as vaccination and B) it does wane over time and people get re-infected if you don't follow that up with a vaccination," University of Virginia Assistant Professor of Medicine Dr. Taison Bell said on Yahoo Finance Live (video above).

Other medical experts have said similar.

“This idea of really building our immunological protection at a population level just based on natural infection, first of all, is super dangerous,” Dr. Keri Althoff, associate professor of epidemiology at Johns Hopkins Bloomberg School of Public Health, told Yahoo Finance. “It’s very hard. We have risk factors for people who are at higher risk for severe illness and death with this, but we have had young, healthy people die of this COVID. We don’t want this virus to just go wild and people lose their lives.”

An estimated 757,000 Americans have died from COVID-19.

Natural immunity 'ought to count too'

Many Americans who decline vaccination against COVID-19 argue that their natural immunity from prior infection should be enough to protect them and others instead of a vaccine.

Furthermore, the argument goes, populations will eventually reach a point of strong immunity against hospitalization and death from COVID-19 through a combination of vaccination and natural immunity — a concept known as endemicity.

Preventive Medicine Specialist Dr. David Katz told Yahoo Finance Live that immunity from natural COVID-19 infection “ought to count too. Those vaccinations should be freed up for others who need them more, whether it's boosters or distributions around the world.”

And Pennsylvania-based St. Luke's University Health Network announced back in September that it would allow such individuals who work for them to defer getting the COVID-19 vaccine for 12 months after their infection.

This comes after a study conducted in Israel found that natural immunity offered stronger and longer-lasting protection against the Delta strain of the coronavirus than those who hadn't been infected but were fully vaccinated.

However, according to Dr. Bell, "the nature of the virus is to come in cycles and waves. And over time when another wave comes, when that natural immunity has gone down, you have a population that's still not protected again. So I fear that's what we're going to see."

Dr. Howie Forman, a professor of radiology and public health at Yale University, told Yahoo Finance that there are "important" caveats that should be taken into consideration with natural immunity.

"Logistically, allowing individuals to substitute prior infection for vaccination requires documentation of prior infection and (less certainly) current antibody status," Forman said. "And then making a decision about durability — i.e. how long can someone be considered to still have immunity."

'No good logic' to get infected instead of vaccinated

A study published by the Centers for Disease Control and Prevention (CDC) found that prior COVID infection does not guarantee an antibody response, meaning that those hoping natural immunity will provide them with an alternative to the COVID-19 vaccine may not be successful.

“It’s one more study that says that a certain percent of the population does not develop antibodies, at least measurable antibodies after infection,” Forman said. “It starts to help us understand which groups are less likely to develop antibodies.”

According to the study, "not all persons recovering from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection develop SARS-CoV-2–specific antibodies. We show that non-seroconversion is associated with younger age and higher reverse transcription PCR cycle threshold values and identify SARS-CoV-2 viral loads in the nasopharynx as a major correlate of the systemic antibody response."

(Non-seroconversion means that the infected person's immune system was not able to develop antibodies despite exposure.)

In other words, younger people seem to be less likely to develop antibodies and development of antibodies depends significantly on their viral load, i.e. the severity of their infection. The higher the viral load, generally, the more likely a person is to have developed antibodies.

Consequently, the CDC report warned against believing natural immunity is definitively more effective than vaccination: "RT-PCR positive persons who experienced COVID-19 symptoms might be less inclined to seek vaccination, believing they are protected, but our results caution against this assumption."

Nevertheless, there are clearly some individuals who would rather gain natural immunity by purposely being infected than getting the vaccine. For example, a group of individuals in Canada held a "COVID party" with the intention of producing antibodies after being exposed to the virus. A number of them were hospitalized as a result.

“There is no good logic that says you should get infected instead of vaccinated,” Forman said. “At least down to the age of 12, the evidence is compelling that vaccination is safer than infection, so nobody should want to get infected instead of getting vaccinated. That’s just a foolish thing to do. It’d be sort of like if you could imagine that a healed bone after a fracture turned out to be as sturdy as a bone that hadn’t been fractured or anything akin to saying that if I break my bone, I’ll have strong bones again. There’s no logic to avoiding it. All it’s doing is introducing higher risks to you.”

All things considered, vaccines are 'the way to go'

There is still much to be learned about the coronavirus and its long-term effects, including how long antibodies created after infection last in a person's system and why some develop them while others don't.

The CDC report indicating varied natural immunity response "doesn’t answer the question of whether people without measurable antibodies but documented prior infections might still have protections,” Forman said. “It doesn’t answer that because it was not intended to answer that question. But it starts to raise serious questions about who doesn’t have immunity after infection.”

And while it’s not clear how many vaccinated individuals previously had a COVID-19 infection, research indicates that those people with "hybrid immunity" from both natural immunity and inoculation might have the strongest antibody response of all.

In any case, the critical factor is vaccination — and booster shots at some point — whether or not prior infection occurred.

Vaccines are “the way to go,” stressed Althoff, the epidemiologist at Johns Hopkins. “We have good data to show people are responding and responding well, and that antibody response hangs in there for quite a few months. The whole discussion about boosters right now is coming into play because that antibody response is starting to wane in some — and that’s especially risky if we see strong evidence that it’s waning... [in] older folks or those types of higher-risk individuals."

Adriana Belmonte is a reporter and editor covering politics and health care policy for Yahoo Finance. You can follow her on Twitter @adrianambells and reach her at [email protected].

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