Immunity is protection against a harmful pathogen — in this case, the virus that causes COVID-19. And while this may sound straightforward, immunity is actually an incredibly complex process.

"The specifics of immunity can not only vary by the pathogen, but by the person," says Dr. David Bernard, medical director of clinical pathology at Houston Methodist. "Add to that the fact that now that we have vaccines, there's also more than one way to develop immunity to COVID-19."

We all have a first line of defense called innate immunity — these are the nonspecific forms of immunity that respond the same way to any and all invading microbes, such as our skin and certain cells and proteins.

The next line of defense, which is called adaptive immunity, is where it gets interesting.

"With adaptive immunity, the body develops cells and antibodies that specifically target one invader, such as the virus that causes COVID-19. Adaptive immunity can arise from previous infection (commonly referred to as natural immunity) or vaccination," explains Dr. Bernard.

Given this, it's no wonder that you might be confused about where you stand as far as your level of protection against COVID-19.

You can have:

• Natural immunity
• Vaccine-induced immunity
• Both natural and vaccine-induced immunity
• No adaptive immunity at all
  
  

Questions arise: Do natural immunity and post-vaccination immunity offer the same level of protection? If you have both are you doubly-protected?

"The people we're most worried about right now are those who either have no immunity at all or only immunity from previous infection," says Dr. Bernard. "However, we don't want people who have immunity following both infection and vaccination to think they're invincible."

Dr. Bernard is here to explain COVID-19 immunity: What we know (and don't know) about each level of the immunity spectrum.

Least protected: Those who are unvaccinated

Considering the COVID-19 pandemic has taken more than 650,000 American lives, there's no question that the people who are most at risk right now are those who are unvaccinated.

"Recent estimates suggest that COVID-19 vaccines have saved a quarter of a million lives and prevented more than 1 million hospitalizations," says Dr. Bernard. "Even with the more serious Delta variant now in the mix, the vaccines are proving to be very successful at their primary job — preventing severe disease, hospitalization and death."

To resolve any lingering feelings of unease you may have toward the vaccines, consider reaching out to your primary care doctor. He or she can help you understand how the vaccines work, the side effects that may occur and the benefits of vaccination. He or she can also provide tips on how to deal with vaccine anxiety and decision-making.

"And for those who are young, healthy and thinking it's fine to just wait and see if they get COVID-19, be aware that even a mild case can be debilitating and may even result in symptoms that linger for months and, potentially, a lifetime. Not to mention the risk of hospitalization and death," adds Dr. Bernard.

The bottom line: If you're not yet vaccinated, now is the time. By getting vaccinated, you reap all the protective benefits of immunity without ever facing the risks that come with COVID-19.

Questionably protected: Those who have only natural immunity

Studies show that the vast majority of people who've recovered from COVID-19 produce the major components that typically facilitate protection — including virus-specific antibodies and trained immune cells.

Despite this, Dr. Bernard stresses that there are too many questions surrounding natural immunity following infection to feel confident about its level of protection.

Here's why immunity following infection isn't enough:

"The immunity that you get following infection and vaccination are not exactly the same. If you look at antibody levels, studies have shown that the levels in most people are higher following vaccination than after infection," explains Dr. Bernard. "Although infection does lead to the development of antibodies to different parts of the virus, most of these have not been shown to protect against reinfection. So, vaccination gives higher levels of the protective antibodies than infection does."

Plus, we don't have an easy way of assessing the immunity that follows infection out in the community.

"For instance, it's not feasible for us to know how robust of an immune response each person mounts during infection or how quickly a person's immunity wanes over time," adds Dr. Bernard.

Put another way: There's no way to say, 'Your immunity should protect you for about eight months,' to one person, and then say, 'Your immunity will only protect you for a few months,' to the next.

"On the other hand, the immunity acquired through vaccination is being actively studied in a controlled, detailed manner through the ongoing COVID-19 vaccine trials. It's information from these studies that's prompted the FDA to make third shots available to those who are immunocompromised and begin discussions about booster shots for everyone else," says Dr. Bernard.

Plus, there's still the risk of getting COVID-19 again.

"Reinfection with COVID-19 is somewhat rare, but it's likely to become more and more common over time and if more concerning COVID-19 variants arise," warns Dr. Bernard.

In fact, a recent study found that unvaccinated adults were twice as likely to get reinfected with COVID-19 than those who got vaccinated after they'd recovered from their illness. And even if your symptoms are more mild the second time around, you could pass the virus to someone who's higher risk.

The bottom line: The natural immunity that you get following infection isn't enough. Even if you've had COVID-19, it's important to get vaccinated once you've recovered.

Most protected: Those who are vaccinated

As mentioned, COVID-19 vaccines have saved a quarter of a million lives and prevented more than 1 million hospitalizations.

But...you also likely know someone who's vaccinated but recently got COVID-19.

"No vaccine is ever 100% effective, and, with the more transmissible Delta variant, we are seeing breakthrough infections occur. The good news, though, is that vaccinated individuals who do get COVID-19 have a much lower risk of being hospitalized," says Dr. Bernard.

And while immunity following vaccination seems to be waning in some regard — particularly in terms of preventing mild and moderate illness for those who were vaccinated very early — the good news is that adaptive immunity can be "boosted" with a third dose.

"Third shots are already available to those who are seriously immunocompromised. And the FDA is reviewing data and finalizing plans to make booster shots available to everyone starting perhaps as early as 8 months after a person's second dose," adds Dr. Bernard.

Plus, with FDA approval of the Pfizer vaccine, your doctor can now prescribe a third dose to you, based on his or her best judgment for off-label prescribing.

In the meantime, vaccines aren't the only safety measure we have in our COVID-19 prevention arsenal. When community spread is high, we still have masks and social distancing we can rely on as extra layers of protection.

The bottom line: You're more protected. If you're immunocompromised, you're eligible to sign up for a third dose. If you're not, you still need to be aware of your surroundings and take precautions during a surge.

If you're vaccinated and you've had COVID-19, are you doubly-protected?

Probably the most confusing end of the immunity spectrum is what it means to have both natural immunity plus post-vaccination immunity.

Look, immunity that comes from infection is complex. And post-vaccination immunity is complex, too. Understanding how these two might work together and whether protection can be additive has yet to be answered.

"Having adaptive immunity following both infection and vaccination may mean you're even more protected, but it may also prove not to be better. I would caution against assuming you're now invincible. To protect yourself and others, you still need to take precautions like masking and social distancing during a surge," warns Dr. Bernard.

It may also mean that you still need a third dose of vaccine.

"Immunity is always something that's fairly individualized, and when you start adding more variables into the equation the answers become less clear," says Dr. Bernard. "Whether and when those with immunity due to infection and vaccination might need booster shots has yet to be determined."

The bottom line: You're not invincible. You still need to take precautions during a surge and may still need a third dose at some point.