Covid-19 Infection Produces Protective Immunity

The pandemic began to enter a new phase in late 2021 when the omicron version of SARS-CoV-2 became widespread. Many people were still unsure if they were at risk of contracting the virus despite having been vaccinated or having had COVID-19 infections in the past.

The pandemic began to enter a new phase in late 2021 when the omicron version of SARS-CoV-2 became widespread. Many people were still unsure if they were at risk of contracting the virus despite having been vaccinated or having had COVID-19 infections in the past.

As of February 20, 2022, approximately 4.9 billion people had received at least one dose. This is 63.9%. Since the outbreak, more than 430,000,000 cases of COVID-19 were confirmed.

With the vast majority of the world’s population either being immunized against COVID-19, or having recovered from infection over the past few years, many people are asking: How long can the immune system be triggered by vaccination, active infection, or a combination thereof?

This is a difficult question, as the virus is still relatively new. New variants of the virus have been constantly discovered. Researchers are now beginning to understand how immunity works to prevent reinfections and to prevent severe COVID-19, which can cause death and hospitalization.

We are immunologists who study inflammatory and infectious diseases including COVID-19. Our goal is to understand the nature of protective immunity.

Antibodies and ‘killer T cells’: What is their role?

Your body will produce two types of immune defenses after being infected with COVID-19 or vaccinated. The first type is B cells which produce antibodies.

Antibodies, Y-shaped proteins, are the first line of defense against infection or perceived invaders. Similar to a lock and key in a lock and keys, antibodies can bind directly to viruses (or to the spike protein COVID-19 in the case of mRNA vaccines) and stop them from entering cells. Antibodies are not effective once the virus has entered cells. The virus spreads to other cells by reproducing in infected cells.

This is when your immune system activates another type of immune cell, the killer T cell. These cells act as your second line of defense.

Killer T cells are not able to detect viruses and prevent them from entering cells. The killer T cells are able to recognize virus-infected cells and destroy them before they can reproduce. Killer T cells can prevent viruses from spreading and multiplying.

The public believed, incorrectly, that antibodies provided the majority of protective immunity during the COVID-19 pandemic. However, they failed to recognize the crucial role played by killer T cells. It is partly because antibodies are simple to detect while killer T-cell detection requires advanced technology. When antibodies fail, killer T cells are responsible for which prevents the more serious outcomes of COVID-19 such as death and hospitalization.

Long-term protective immunity is dependent on memory

Next comes the true veterans of the immune system who can provide strong immunity and long-lasting protection against infection based on their previous experience.

After clearing the virus or its spike protein, the antibodies-producing B cells (and killer T cells) are converted into memory cells. These cells recognize the threat and respond quickly to prevent infection by recognizing the same protein as the virus.

This is why multiple doses of COVID-19 vaccines, which increase the number of memory cells and prevent reinfections – or breakthrough infection – work better than a single dose. A similar increase in memory-killing T cells helps to prevent severe illness and hospitalization.

The immune system can keep memory cells in place for long periods of time – sometimes even up to 75 years. This is why certain cases of measles or smallpox can lead to lifelong protective immunity.

However, memory cells are very specific. Memory cells might not be as effective if new viruses or strains emerge, as was the case many times during COVID-19.

This begs the question: When and for how long will these key players of our immune system emerge from infection?

Durability and long-term immunity to COVID-19

After infection with COVID-19, or after the vaccination, antibodies start to mobilize within the first few days. Their concentration steadily increases for several weeks and months. People have an immune response that is strong within three months of infection. This is why the Centers for Disease Control and Prevention has long held that waning immune” in the fall of 2021, months after people were fully vaccinated.

But immunity is complex and nuanced and antibodies are only one part of it. Some B cells can live for a long time and continue to produce antibodies against viruses. Antibodies against SARS-CoV-2 were detected even after an infection. Similar to memory B cells, which can be detected for at most eight months, memory killer T cells can also be detected for close to 2 years after COVID-19 infections.

In general, vaccines are also known to cause an immune memory that is similar to natural infection. Long-term studies on the comparison are not yet available. However, a new study, that has not been peer-reviewed, showed that the third dose of vaccine increases B cell diversity. This leads to greater protection against variants such as omicron.

However, the detection of an immune response doesn’t guarantee protection against COVID-19.

It is difficult to correlate the protection offered by antibodies and killer cells with the amount of COVID-19 because of the time and research required.

It is now clear that there may be an immune response to the virus, but not enough to protect against reinfection.

Immunity to infection from vaccination

A recent U.K. Health Security Agency study showed that two doses of vaccine can protect against infection for up to six weeks. Another study found that the protective effect of mRNA vaccines was high at two months. However, their effectiveness dropped to seven months due to the emergence and decline. Both studies showed that the vaccines performed better in preventing death and hospitalization than they did in preventing infection over time.

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There are conflicting reports about whether protective immunity that is triggered by active infection is superior to that produced by current vaccines. This could have been due to the different strains of the virus that emerged during the study.

The consensus is that COVID-19 can provide protection comparable to that provided by the vaccines. However, this was not peer-reviewed.

Hybrid immunity

Researchers also discovered that protective immunity from a combination of COVID-19 and vaccination, called hybrid immunity, is very powerful. This protection remains active for over a year following infection with COVID-19.

Hybrid immunity is a unique form of hybrid immunity that triggers a strong antibody response for a prolonged period.

Immunologists are working to find vaccines that trigger the same long-term immune response to reinfect others. This is a growing fact. The hybrid immunity of those who have been vaccinated but also have COVID-19 infection could provide some clues.

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