As a learner Immune response to respiratory infections, I have been following news about new variants of the coronavirus. I want to know whether vaccination or previous infections can provide protection against the SARS-CoV-2 strain, especially the new, Highly transmittable Delta variant, Including Quickly spread to at least 70 countries.

A person can develop immunity in two ways-the ability to resist infection: after being infected with a virus or being vaccinated. However, immune protection is not always equal. SARS-CoV-2 vaccine immunity and natural immunity may be different in the following aspects The strength of the immune response or Duration of protectionIn addition, not everyone has access to Have the same level of immunity to infection, And the immune response to the vaccine is Very consistent.

The difference in immune response between vaccination and infection appears to be uniform Bigger when dealing with new variantsIn early July, two new studies were published showing that the COVID-19 vaccine is slightly less effective than against older strains. Still seems to provide an excellent immune response Oppose the new variants.Researchers have studied how antibodies bind to new variants of the coronavirus and found people who had previously been infected with the coronavirus May be sensitive to new strains, And vaccinated people are more likely to be protected.

The COVID-19 vaccine provides a safe and reliable way to develop immunity against two older strains of coronavirus And fight against emerging strains, especially the new Delta variants.

Immunity after infection is unpredictable

Immunity comes from the ability of the immune system to remember infections. Using this immune memory, the body will know how to fight infection when it encounters a pathogen again. Antibodies are proteins that can bind to viruses and prevent infection. T cells direct the removal of infected cells and viruses that have been bound by antibodies. These two are the main players that contribute to immunity.

After being infected with SARS-CoV-2, a person’s Antibody Reacting with T cells can provide Prevent reinfectionApproximately 84% to 91% of people are unlikely to be infected again after developing antibodies to the original strain of coronavirus Six months, Even if Mild infectionPeople who have no symptoms during the infection may also develop immunity, although they tend to Fewer antibodies Than those who feel uncomfortable. So for some people, natural immunity may be strong and lasting.

A big problem is that not everyone will develop immunity after being infected with SARS-CoV-2.As many as 9% of infected people do not Detectable antibody, Up to 7% T cells that do not recognize the virus 30 days after infection.

For people who have developed immunity, Intensity and duration The protection can be very different.Up to 5% of people may Loss of immune protection In a few months. Without a strong immune defense, these people can easily be infected with the coronavirus again. Some people get the second COVID-19 infection in the first place One month after the first infection; And, although this happens rarely, some people have Be hospitalized Or even died After being infected again.

A growing problem is that people who were previously infected by strains that existed early in the pandemic may be more susceptible to reinfection with Delta variants.A recent study found 12 months after infection, 88% of people still have antibodies that can prevent the original coronavirus from infecting cultured cells-but Less than 50% There are antibodies that can block Delta variants.

Most importantly, people who are infected may also spread the coronavirus, even if Not sick. In this case, the new variant is particularly problematic because They spread more easily Than the original strain.

Reliable protection from vaccination

COVID-19 vaccine is produced at the same time Antibody and T cell response – These reactions are stronger and more consistent than the immune system after natural infection. A study found that six months after receiving the first dose of Moderna vaccine, 100% of people tested have antibodies against SARS-CoV-2. This is the longest period of published research reports so far. In a study of Pfizer and Moderna vaccines, the vaccinated people also had much higher antibody levels than the vaccinated people. Recovery from infection.

Better yet, a Study in Israel It showed that the Pfizer vaccine prevented 90% of infections after both doses-even if there were new mutations in the population.And one Reduced infections This means that people are unlikely to spread the virus to those around them.

For those who have been infected with the coronavirus, vaccination still has great benefits.A study of the original COVID-19 virus showed that vaccination after infection will produce approximately 100 times more antibodies Compared with infection alone, 100% of people vaccinated after infection Protective antibodies against Delta variants.

COVID-19 vaccines are not perfect, but they produce powerful antibodies and T cell responses, providing safer and more reliable protection than natural immunity—especially when new variants are loose.

This is an updated version Article originally published May 25, 2021.

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

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