Jennifer T. Grier, University of South Carolina

A few weeks ago a message popped up in the corner of my screen. “What do you think of people who recently had COVID-19 to get the vaccine?” A friend of mine was eligible for a COVID-19 vaccine but had recently gotten over SARS-CoV-2 infection. More people can be vaccinated each week – including millions of people who have already recovered from coronavirus infection. Many wonder if they need the vaccine, especially people who are already infected.

I study immune responses to respiratory infections, so I get a lot of these questions. A person can develop immunity – the ability to resist infection – when infected with a virus or given a vaccine. However, the immune protection is not always the same. The strength of the immune response, the duration of protection, and the variation in immune response between people differ greatly between vaccine immunity and natural immunity to SARS-CoV-2. COVID-19 vaccines offer safer and more reliable immunity than natural infections.

Electron microscope image of four SARS-CoV-2 particlesThe immune system usually produces an immune response to SARS-CoV-2 infection, but not always. National Institute for Allergies and Infectious Diseases, CC BY

Post-infection immunity is unpredictable

Immunity is based on the immune system’s ability to remember an infection. It is with this immune memory that the body can struggle when it comes across the disease again. Antibodies are proteins that bind to a virus and can prevent infection. T cells are cells that direct 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 be strong enough to protect against re-infection. Research shows that 91% of people who develop antibodies to the coronavirus are unlikely to get reinfected for six months, even if they are mildly 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. For some people, natural immunity can be strong and long lasting.

The problem is that not everyone develops immunity after SARS-CoV-2 infection. Up to 9% of those infected have no detectable antibodies, and up to 7% of people 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 a few months. Without a strong immune system, these people are prone to re-infection from the coronavirus. Some had a second attack of COVID-19 just a month after their first infection; and although rare, some people were hospitalized or even died.

A person who is infected again may also be able to transmit the coronavirus without feeling sick. This could endanger the relatives of the person.

And what about the variants? So far there is no exact data on the new coronavirus variants and natural immunity or reinfection, but it is entirely possible that the immunity to infection is not as strong against infection with another variant.

A healthy human T-cell, a big blue crumpled ballCOVID-19 vaccines produce a strong immune response to both antibodies and T cells, like the T cell in this photo. National Institutes for Allergies and Infectious Diseases / National Health Institutes

Vaccination leads to reliable protection

COVID-19 vaccines produce both antibody and T cell responses – however, this is much stronger and more consistent than immunity to natural infections. One study found that four 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 that has been studied so far. In a study of the Pfizer and Moderna vaccines, antibody levels were also much higher in people who had been vaccinated than in people who had recovered from infection.

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

The COVID-19 vaccines are not perfect, but they produce strong antibody and T-cell responses that offer a safer and more reliable means of protection than natural immunity.

Infection and vaccination together

I immediately replied to my friend’s message that she should have the vaccine. After the vaccination, my friend might be comfortable knowing that she has long-lasting, effective immunity and less chance of spreading the coronavirus to her friends and family.

But more good news has surfaced since I sent this message. A new study showed that vaccination after infection produces six times more antibodies than a vaccine alone. This doesn’t mean everyone should try to get infected before vaccination – vaccine immunity alone is more than strong enough to provide protection, and the dangers of fighting COVID-19 far outweigh the benefits. But when my friend and the many others who have already been infected get their vaccines, they will be well protected.

Natural immunity to infection is just far too unreliable in the face of such a devastating virus. Current COVID-19 vaccines provide incredibly powerful and consistent protection for the vast majority of people. For all beneficiaries, including those who have already had SARS-CoV-2 infection, COVID-19 vaccines offer immense benefits.The conversation

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

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