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Delta Variant Makes It Even Extra Vital to Get a COVID-19 Vaccine, Even when You’ve Already Had the Coronavirus

By Jennifer T. Grier, University of South Carolina

As someone studying immune responses to respiratory infections, I have followed the news of the emerging coronavirus variants with concern. I wondered if a vaccination or previous infection would offer protection from SARS-CoV-2 strains, especially the new, highly transmissible Delta variant that has quickly spread to at least 70 countries.

A person can develop immunity – the ability to resist infection – in two ways: either after infection with a virus or through vaccination. However, immune protection is not always the same. Vaccine immunity and natural immunity for SARS-CoV-2 may differ in terms of the strength of the immune response or the duration of protection. In addition, not everyone will get the same level of immunity to infection while immune responses to the vaccines are very consistent.

The difference in the immune response between vaccination and infection seems to be even greater with new variants. Two new studies were published in early July showing that COVID-19 vaccines, although slightly less effective than the older strains of the virus, still offer an excellent immune response against the new variants. The researchers looked at how antibodies bind to new variants of the coronavirus and found that people who were previously infected with the coronavirus might be susceptible to the new strains, while people who were vaccinated were more likely to be protected.

COVID-19 vaccines provide a safe and reliable route to immunity against both older strains of coronavirus and emerging strains, especially the new Delta variant.

Post-infection immunity is unpredictable

Immunity arises from the immune system’s ability to remember an infection. With this immune memory, the body knows how to fight off an infection if it encounters the pathogen again. Antibodies are proteins that bind to a virus and can prevent infection. T cells control the removal of infected cells and viruses that are already bound by antibodies. These two are some of the key players that contribute to immunity.

After a SARS-CoV-2 infection, a person’s antibody and T-cell responses can protect against re-infection. About 84 to 91% of people who developed antibodies to the original strains of coronavirus were unlikely to become infected again for six months, even after being slightly infected. People who didn’t have symptoms during the infection are also likely to develop immunity, although they tend to make fewer antibodies than those who felt sick. So, for some people, natural immunity can be strong and long-lasting.

A big problem is that not everyone develops immunity after being infected with SARS-CoV-2. Up to 9% of those infected have no detectable antibodies and up to 7% do not have T cells that can recognize the virus 30 days after infection.

In people who develop immunity, the strength and duration of protection can vary widely. Up to 5% of people can lose their immune protection within a few months. Without a strong immune system, these people are prone to reinfection from the coronavirus. Some had second bouts of COVID-19 as early as a month after their first infection; and although it is rare, some people have been hospitalized or even died from re-infection.

A growing problem is that people previously infected with strains that were previously present in the pandemic may be more susceptible to reinfection from the Delta variant. A recent study found that 88% of people 12 months after infection still had antibodies that could block cultured cells from infecting cells with the original coronavirus variant – but less than 50% had antibodies that could block the Delta variant .

To top it off, an infected person can potentially also transmit the coronavirus without feeling sick. The new variants are particularly problematic here, as they are more easily transferred than the original strains.

Vaccination leads to reliable protection

COVID-19 vaccines produce both antibody and T cell responses – and these responses are much stronger and more consistent than immunity from natural infection. One study found that six months after receiving the first dose of the Moderna vaccine, 100% of the people tested had antibodies to SARS-CoV-2. This is the longest period reported in published studies to date. In a study of the Pfizer and Moderna vaccines, antibody levels were also much higher in people who had been vaccinated than in those who had recovered from infection.

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Even better, a study in Israel showed that the Pfizer vaccine blocked 90% of infections after both doses – even when new variants were present in the population. And a decrease in infections means people are less likely to spread the virus to those around them.

For those who have already contracted the coronavirus, vaccination still has a huge benefit. A study of the original COVID-19 virus showed that vaccination after infection produced about 100 times more antibodies than infection on its own, and 100% of people vaccinated after infection had protective antibodies against the delta Variant.

The COVID-19 vaccines aren’t perfect, but they produce strong antibody and T-cell responses that offer safer and more reliable protection than natural immunity – especially with new varieties in the field.

This is an updated version of an article originally published on May 25, 2021.The conversation

Jennifer T. Grier, Assistant Clinical Professor of Immunology, University of South Carolina

This article was republished by The Conversation under a Creative Commons license. Read the original article.

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