Why vaccination is still crucial in the fight against the Delta variant, according to experts.

As the Delta variant surges across the United States, the Centers for Disease Control and Prevention (CDC) recommends that anyone eligible should get the vaccine—including those who have been infected with COVID-19 in the past.

While antibodies from a COVID-19 infection may offer some degree of protection against another future infection (known as "natural immunity"), those who have already had the virus may still be vulnerable—perhaps especially to the Delta variant, the current predominant strain, which is nearly twice as contagious as previous variants. In fact, a study published by the CDC on August 6 compared reinfection rates of people who had previously had COVID-19 and found that unvaccinated individuals were more than twice as likely to be reinfected than fully vaccinated individuals.

For that reason, experts don't recommend relying on natural immunity alone to prevent a COVID-19 infection. Here's what you need to know about how to protect yourself and others from the Delta variant and other strains.

natural immunity vs vaccine

Do experts recommend I still get the vaccine if I've had COVID-19 already?

All infections provide some degree of protection from future sickness by producing antibodies. "When you get infected with a virus, you make an immune response against it, just like you do with a vaccine," Seema S. Lakdawala, PhD, an associate professor of microbiology and molecular genetics at the University of Pittsburgh School of Medicine, tells Health. According to Lakdawala, the immune system creates antibodies and T-cells to the specific virus, which respond when they "see" that virus again.

That immune response may help fight off a further infection, Amesh A. Adalja, MD, a senior scholar at Johns Hopkins Bloomberg School of Public Health's Center for Health Security, tells Health. The problem is SARS-CoV-2, the virus that causes COVID-19, continues to mutate, so that original protection may not be effective on new mutations. "When you get infected, you become immune to viruses that are similar," says Lakdawala. "But the whole point of viruses is to continue to spread, so they evolve and change."

For example, Taylor Heald-Sargent, MD, an assistant professor of pediatrics specializing in infectious diseases at Northwestern University Feinberg School of Medicine, explains that if you had COVID-19 during the initial outbreak in spring 2020, it's more likely than not that your antibodies don't measure up against the Delta strain.

And according to Dr. Heald-Sargent, while one person may have some degree of immunity to the Delta variant from a previous infection, the level of protection can drastically vary between individuals. For example, she says, an immunocompromised person may mount a weaker immune response than other individuals. Those who had milder forms of COVID-19 may also have weaker antibodies, Joshua LaBaer, PhD, MD, executive director of the Biodesign Institute at Arizona State University, tells Health.

But no matter the severity, a past COVID-19 diagnosis isn't a guarantee of protection: A study conducted by the University of Oxford found that people with weaker immune responses from a previous infection could be at a higher risk of contracting one of the new variants of COVID-19. "We are definitely seeing lots of examples of people who had the infection in the past and who got re-infected despite that, both with the Delta variant and previous strains," explains Dr. LeBaer.

What should I know about antibodies, vaccines, and the Delta variant?

The CDC officially recommends vaccination for all eligible individuals, including those who have already had COVID-19 in the past. Compared to natural immunity, Dr. Adalja says immunity from vaccination is stronger, more robust, and more predictable — making it the best route for protecting against severe illness from the Delta strain.

While an infection creates antibodies against all the proteins in a particular viral strain, vaccination is more focused on neutralizing the most important protein. "The spike protein, which binds to receptors to get inside a person's cells, is the most important protein for a wide variety of strains," says Lakdawala. Antibodies against the virus' spike proteins neutralize the entire virus, she explains, which prevents it from entering the cells and making you sick.

Vaccines also provide more antibodies to fight off a new infection. Dr. LeBaer says while people who have been infected may have antibodies in their blood, those antibodies increase considerably upon vaccination.

And due to the increased antibodies, when the vaccine protection starts to wear off, people might be protected longer. "The vaccine elicits many more antibodies than a natural infection, so as the vaccine declines, the protection lasts longer than it would from a natural infection," says Dr. Heald-Sargent.

While she says vaccines won't totally protect you from sickness, Dr. Heald-Sargent adds that all three vaccines currently allowed by the FDA's emergency use authorization offer some protection against severe sickness—including from the Delta variant.

"When it comes to what matters, preventing serious disease, hospitalization, and death, all three vaccines are extremely reliable," explains Dr. Adalja. "It's extremely unlikely that anyone who's been fully vaccinated would die from any emerging strains of COVID-19, including the Delta strain."

And even if you are already vaccinated against COVID-19, experts encourage continued masking and physical distancing in public spaces, especially if you live in a high-transmission area. "Even if you're vaccinated, you can still have an infection," says Dr. Heald-Sargent. "It might not make you sick, but you could still transmit it to someone else."

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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