For many diseases, achieving herd immunity – when the population hits a certain threshold of resistance against a disease – is the most effective way to reduce the spread of infection. In the case of COVID-19, immunity can be granted through vaccination, infection, or both.

A big debate around the topic of COVID-19 vaccines is whether greater immunity is granted after infection or vaccination. People on the right are more likely to perceive natural immunity – immunity developed after a COVID-19 infection – as more effective and longer lasting than the vaccine. Many on the left think the exact opposite.

Most estimates place the threshold of COVID-19 herd immunity at 60-80% of the U.S. population. However, the issue is a lot more complicated than that.

The medical community has long accepted that both vaccine effectiveness and natural immunity wane over time – and they do so at varying rates. Breakthrough infections are not unique to COVID-19, and booster shots for other vaccines have been available to the public for dozens of years.


Vaccine-induced vs. Natural Immunity: Which is Better?

While there is some research on this topic, many studies contradict each other, and are often not peer-reviewed. More research will have to be done on vaccine-induced vs. natural immunity to truly understand which is more effective in preventing cases, hospitalization, and death long-term. In addition, the vaccine may be better protective for some individuals vs. natural immunity for others. 

Moral of the story: we just don’t know yet, but we can look at preliminary data to get a small glimpse of what’s going on.

The Centers for Disease Control and Prevention (CDC) describes that “evidence suggests that reinfection with the virus that causes COVID-19 is uncommon in the 90 days after initial infection. However, experts don’t know for sure how long this protection lasts, and the risk of severe illness and death from COVID-19 far outweighs any benefits of natural immunity.”

Various studies on COVID-19 immunity appear to contradict each other. Some are not peer-reviewed, meaning experts have not critically evaluated them for false assumptions, conclusions, biases in methodology, misleading conclusions, etc. Why? Because peer-review is a very lengthy process and is taken very seriously. Experts may disagree on some of the studies mentioned in this article. Our goal is to provide you perspective on the topic, and highlight some popular studies being cited on both sides of the vaccine debate.

A well-known study from the Cleveland Clinic, published in June, concluded that “individuals who have [been infected] are unlikely to benefit from COVID-19 vaccination.” The study, conducted on Clinic members, found that both the vaccine and previously infected people without vaccination were well-protected from getting infected with COVID-19. It also found that vaccination was not “associated with a significantly lower risk” of infection among previously-infected people. The study is not peer-reviewed.

The study was conducted before the surge of the Delta variant, however, and the Clinic released a statement in August stating that “More research is needed. We do not know how long the immune system will protect itself against re-infection after COVID-19… It is also important to keep in mind that this study was conducted in a population that was younger and healthier than the general population.”

Another non-peer-reviewed study in Israel found that natural immunity provides longer-lasting, stronger protection against infection and hospitalization during the spread of the Delta variant of COVID-19. The study also found that natural immunity may decrease slowly over time, but that one dose of the Pfizer COVID-19 vaccine doubles an individual’s protection against contracting it again.

Research funded by the National Institute of Allergy and Infectious Diseases (NIAID) found in January that the vast majority (95%+) of people previously infected with COVID-19 have strong antibody responses up to eight months after infection, while levels in some people slowly waned over time. This research was published before the Delta variant was the dominant strain of COVID-19 in the U.S.

Research shows that natural immunity creates a strong protection against COVID-19 reinfection. Of course, a great disadvantage of natural immunity is that it requires a previous infection, and people don’t (generally) seek out natural immunity.

In other words, natural immunity is by chance. Its risk has led to millions of deaths around the world, and countless dollars in hospitalization costs. Some people also have long-term effects due to disease caused by COVID-19 infection – that is, symptoms such as fatigue, chest pain, memory problems, and many others are sometimes prevalent more than 12 weeks after a COVID-19 diagnosis.


More data analysis from AllSides: Throughout the pandemic, COVID-19 has averaged out to be the third-highest cause of death in the United States, according to numbers from the CDC.


An article by the CDC published in September found that out of a 72 person study, only 46 people (64%) developed antibodies against COVID-19 more than three weeks after an asymptomatic case. Compared to symptomatic, this shows that asymptomatic cases may be less likely to create a strong antibody response against future infection. Another similar real-world study found that 94% of people who were mildly infected with COVID-19 had a reduction in antibodies after 60 days.

What research does suggest is that vaccination after infection has a substantial impact on antibody production against COVID-19 – this is sometimes referred to as “hybrid immunity.”

A non-peer reviewed study in the UK found that vaccination – even one shot of the Pfizer vaccine – greatly boosts antibody and memory responses in people who were previously infected and likely already have some immunity to the disease.

Similarly, a widely-cited study from the CDC published in August found that, after infection, unvaccinated people are 2.34 times more likely to be reinfected with COVID-19 compared to fully vaccinated people who were previously infected. 


Side Effects & Adverse Events After COVID-19 Vaccination

People on the right are more likely to talk about side effects from COVID-19 vaccines. Some believe the vaccines may be unsafe or were developed too quickly, and argue that the vaccine’s risks currently outweigh the risks associated with contracting COVID-19. People on the left are more likely to argue that the potential risks from COVID-19 infection are worse than the potential risks of the vaccine, suggesting that the benefits of vaccination greatly outweigh the drawbacks – such as increased risk of infection or death due to COVID-19.

Most people know that common symptoms of COVID-19 vaccination include feeling tired, headaches, fevers, and a sore arm. Usually, these only last for a day or two and then disappear. The real concern among some people are potential long-lasting or severe effects – including death due to COVID-19 vaccination or unknown side effects showing up in the future. These concerns are keeping many people from getting the shot.

The CDC has reported on some serious adverse events after vaccination, such as myocarditis and Guillain-Barré Syndrome, stating that they occur in approximately every eight and 13 people per million people vaccinated, respectively. Research is now underway to examine if there is a link between the vaccine and menstrual changes in women – the National Institutes of Health (NIH) has allotted $1.6 million to "explore potential links between COVID-19 vaccination and menstrual changes," according to a press release.

The Vaccine Adverse Event Reporting System (VAERS) is a U.S. government database that contains unverified reports of adverse events after vaccination. Reports are accepted from anyone, meaning that many reports in the system are not confirmed by professionals.

Healthcare providers are required by law to report life-threatening adverse events, deaths, and vaccine administration errors to VAERS. They are also advised to report any “clinically significant” adverse events, regardless of if the vaccine caused the event or not.

This means some adverse events recorded in VAERS, including 7,400+ deaths reported in the database, might not be vaccine-related. Rather, the purpose of VAERS is to be an early warning system for potential conditions that may be attributed to the vaccines. Limitations of the database include the fact that serious adverse events are more likely to be reported than minor adverse events, and a relationship cannot be established between the COVID-19 vaccine and adverse effects using only the database alone.

In addition, many reports in the system are coincidental, so misinterpretation of the data often feeds into narratives on both sides of the vaccine divide. For example, as of September 3rd, VAERS reported over 5,000 falls and over 1,000 urinary tract infections after COVID-19 vaccinations, but it would be difficult to prove that the vaccine caused a fall or urinary tract infections, which are both very common among the general public.

This doesn’t mean that VAERS should be ignored, either. The database collects information on the individual (e.g. age, sex, vaccination date) and outcome of adverse events to find potential causes of adverse events, such as myocarditis, in COVID-19 vaccines – as rare as they might be.

Despite all of this, people who are choosing not to get the vaccine at this time are still more likely to believe that the COVID-19 vaccine has the potential of being more harmful than the disease itself. In part 1 of our “The COVID-19 Vaccine Divide” series, we looked at perceptions of the COVID-19 vaccines.


Be on the lookout for part 3 of our series on COVID-19 vaccines, which will examine vaccine mandates in the United States, their constitutionality, and what the public thinks of them. 

You can use AllSides to find more perspectives on the COVID-19 pandemic and COVID-19 vaccines.


Andrew Weinzierl is AllSides’ Research Assistant and Data Journalist. He has a Lean Left bias.

This piece was reviewed by Managing Editor Henry A. Brechter (Center bias) and Julie Mastrine, Director of Marketing and Bias Ratings (Lean Right).