Can Double COVID-19 Immunity Defeat the Delta Variant?

As the COVID-19 pandemic continues, many people ask which type of immunity offers the best defense against the SARS-CoV-2 variant Delta.

Immunity to disease results when antibodies are developed in a person's system to that particular disease, says the U.S. CDC. Moreover, antibodies are produced from both vaccines and virus infections.

According to new reports, a significant number of people already have both vaccine-generated and natural infection antibodies.

Seroprevalence data published by the UK’s Public Health England on August 26, 2021, shows approximately 97.7% of adult blood donors have SARS-CoV-2 coronavirus antibodies from either infection or vaccination.

And as of March 2021, the Red Cross indicated about 20% of its blood donations contained antibodies from unvaccinated people.

Do these reports indicate people such as Texas Governor Gregg Abbott and NFL Tennessee Titan football quarterback who were fully vaccinated with the mRNA Comirnaty vaccine and recently tested positive for SARS-CoV-2 now have ‘double-immunity'?

Dr. Francis S. Collins, the 16th Director of the National Institutes of Health (NIH), appointed by President Barack Obama, stated in his weekly blog on August June 22, 2021, ‘a new NIH-supported study shows that the answer to the immunity question will vary based on how an individual’s antibodies against SARS-CoV-2 were generated… through a naturally acquired infection or from a COVID-19 vaccine.’

Dr. Collins’s blog is excerpted below:

The new evidence shows that protective antibodies generated in response to an mRNA vaccine will target a broader range of SARS-CoV-2 variants carrying “single letter” changes in a vital portion of their spike protein compared to antibodies acquired from an infection.

In a recent study published in the journal Science Translational Medicine, Bloom, Greaney, and colleagues looked at the thousands of possible receptor-binding domain (RBD) variants to understand how antibodies might be expected to hit their targets there. 

These researchers wanted to explore any differences between RBD-directed antibodies based on how they were acquired.

First, they created libraries of all 3,800 possible RBD single amino acid mutants and exposed the libraries to samples taken from vaccinated and unvaccinated individuals who’d been previously infected. 

These vaccinated individuals had received two doses of the Moderna mRNA vaccine, known as SpikeVax.  

This mRNA vaccine works by prompting a person’s cells to produce the spike protein, thereby launching an immune response and producing antibodies.

By closely examining the results, the researchers uncovered essential differences between acquired immunity in people who’d been vaccinated and unvaccinated people who’d been previously infected with SARS-CoV-2.  

Specifically, antibodies elicited by the mRNA vaccine were more focused on the RBD compared to antibodies produced by an infection, which more often targeted other portions of the spike protein. 

Notably, the vaccine-elicited antibodies targeted a broader range of places on the RBD than those elicited by natural infection.

These findings suggest that natural immunity and vaccine-generated immunity to SARS-CoV-2 will differ in recognizing new viral variants. 

What’s more, antibodies acquired with the help of a vaccine may be more likely to target new SARS-CoV-2 variants potently, even when the variants carry new mutations in the RBD.

It’s not entirely clear why these differences in vaccine versus infection-elicited antibody responses exist. However, both cases acquire RBD-directed antibodies from the immune system’s recognition and response to viral spike proteins. 

Research suggests these differences may arise because the vaccine presents the viral protein in slightly different conformations.

Also, mRNA delivery may change the way antigens are presented to the immune system, leading to differences in the produced antibodies. 

Another difference is that natural infection only exposes the body to the coronavirus in the respiratory tract (unless the illness is very severe). Instead, vaccines are delivered to muscle, where the immune system may have an even better chance of seeing it and responding vigorously.

Whatever the underlying reasons turn out to be, it’s important to consider that humans are routinely infected and re-infected with common coronaviruses, such as viruses responsible for the common cold. 

It’s not at all unusual to catch a cold from seasonal coronaviruses year after year. That’s at least in part because those viruses tend to evolve to escape acquired immunity, much as SARS-CoV-2 is now in the process of doing.

The hope is that acquired immunity from the vaccines will indeed produce long-lasting protection against SARS-CoV-2 and its evolving variants and bring an end to the COVID-19 pandemic, stated Dr. Collins’s blog.

However, breaking news from Israel’s Ministry of Health indicates some people can become SARS-CoV-2 infected even after a third mRNA COVID-19 vaccination. The risk of infection, hospitalization, and death are all much lower in vaccinated compared to unvaccinated people.

Furthermore, as of August 23, 2021, the CDC received reports from 49 states and territories of 11,050 COVID-19 vaccinated patients with ‘breakthrough infections’ who were hospitalized or died.

People who are immunocompromised may not be protected even if fully vaccinated and may be more likely to have a breakthrough infection. They should continue to take all precautions recommended for unvaccinated people, until advised otherwise by their healthcare provider.

CoronavirusToday.com publishes a comprehensive listing of studies related to vaccine-induced and natural immunity on this webpage.  

PrecisionVaccinations publishes fact-check, research-based vaccine news.

Updated for clarity on August 29, 2021.