How long does immunity last for viral infections with and without vaccinations?

January 31, 2024

How Long Does Illness Immunity Last After Being Sick?

Introduction

A body’s immune system plays an important role in combating and recovering from disease. Meanwhile, vaccines can be very effective in giving the body a measure of protection from the recurrence of various diseases. But how long immunity lasts can depend on various factors, such as whether the immunity is natural, induced by a vaccine, or hybrid. The length of time that immunity lasts varies from person to person, and there is no consensus on the specific length of time that it can be effective.

How Natural Immunity Works After Viral Infections

The body’s immune system is effective in destroying a virus if the person has been infected with it earlier. The immune cells and proteins that are in the body can recognize and kill the pathogen if it strikes again. Antibodies are proteins that circulate in the blood. They recognize foreign substances like viruses and neutralize them. Helper T cells help to recognize pathogens.

Killer T cells kill pathogens. B cells create new antibodies when the body requires them.

While people who recover from COVID-19 have all these four components, it is not known exactly how long the immunity will last and how effective it will be against different strains of the virus. What is clear is that the protection wanes after a period of time, usually a year, which is why this is the recommended period for vaccination.

How Vaccine-Induced Immunity Works

The four vaccines authorized for use in adults in the United States are from Pfizer-BioNTech, Moderna, Novavax, and Johnson & Johnson. All four vaccines work by helping the body develop immunity to the virus that causes COVID-19 without the person having to develop COVID-19.Pfizer and Moderna vaccines are effective at reducing the risk of COVID-19, including severe illness, by 90% or more in people who are fully vaccinated. The Johnson & Johnson vaccine was 76% effective in preventing COVID-19 infections and 81% effective in preventing COVID-related hospitalization. A Phase 3 clinical trial of 30,000 adults in Mexico and the US found that Novavax was 90.4% effective in preventing symptomatic COVID-19 disease. 

How Hybrid Immunity Protects the Most

Hybrid immunity can provide protection for more than a year. After someone has had a natural infection and then gets vaccinated, they get a terrific boost in their antibody levels. Very high antibody levels mean a longer duration of protection. Laboratory results show that these antibodies also provide better protection against variants.

It is recommended that everyone who is 5 years and older get a booster shot. This is because data suggest that vaccination becomes less effective over time, especially in people 65 and older and at preventing infection or milder illness with symptoms.

The evidence suggests that hybrid immunity protects the most, followed by vaccine-induced immunity and natural immunity. As new variants of the Covid-19 virus emerge, there may be a need for an annual booster shot. This may become standard, especially to protect against new variants of the virus that causes COVID-19. Although the vaccines have a wide impact, they are not 100% effective.

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