Delta variant makes getting a COVID-19 vaccine even more important, even if you’ve had the coronavirus before

Immunity after infection is unpredictable

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

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After infection with SARS-CoV-2, a person’s antibody and T cell responses may provide protection against reinfection. It is unlikely that around 84% to 91% of people who developed antibodies to the original strains of coronavirus would be re-infected for six months, even after a mild infection. People who have not had any symptoms during infection are also likely to develop immunity, although they tend to produce fewer antibodies than those who have felt sick. So, for some people, natural immunity can be strong and long lasting.

A big problem is that not everyone will develop immunity after infection with SARS-CoV-2. Up to 9% of those infected do not have detectable antibodies and up to 7% do not have T cells that recognize the virus 30 days after infection.

For people who develop immunity, the strength and duration of protection can vary widely. Up to 5% of people can lose their immune protection within months. Without strong immune defense, these people are susceptible to reinfection with the coronavirus. Some have had second episodes of COVID-19 as early as a month after their first infection; and, although this rarely happens, some people have been hospitalized or even died after reinfection.

A growing problem is that people who have already been infected with strains that were present earlier in the pandemic may be more likely to be re-infected with the delta variant. A recent study found that 12 months after infection, 88% of people still had antibodies that could block the infection of cultured cells with the original variant of the coronavirus – but less than 50% had antibodies that could block the infection. delta variant.

To top it off, an infected person may also be able to transmit the coronavirus, even without feeling sick. The new variants are particularly problematic in this case, as they are transmitted more easily than the original strains.

Vaccination leads to reliable protection

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

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Better yet, a study in Israel showed that the Pfizer vaccine blocked 90% of infections after the two doses – even with new variants present in the population. And fewer infections mean people are less likely to pass the virus on to those around them.

For those who have already been infected with the coronavirus, there is always a big advantage to getting vaccinated. A study with the original COVID-19 virus showed that vaccination after infection produced about 100 times more antibodies than infection alone, and 100% of people vaccinated after infection had protective antibodies against the delta variant. .

COVID-19 vaccines aren’t perfect, but they produce strong antibody and T-cell responses that provide a safer and more reliable means of protection than natural immunity, especially with new variants in the wild.

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

This article is republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Jennifer T. Grier, University of South Carolina.

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Jennifer T. Grier does not work, consult, own stock or receive funding from any company or organization that would benefit from this article, and has not disclosed any relevant affiliation beyond her academic position. .