Posts Make False Comparisons Between COVID-19 Immunity From Infections and Vaccines
SciCheck Digest
Vaccination and infection both provide protective immunity to COVID-19, particularly against severe disease. But gaining immunity through infection is far riskier than vaccination. Posts citing a new Lancet study omit that important context and also misleadingly claim the study shows immunity after infection is superior to vaccination immunity. A co-author of the study told us there was “insufficient data to definitively state” immunity from infection is superior.
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COVID-19 vaccination and infection each provide some temporary protection against future infection and stronger, longer-lasting protection against severe illness.
A recent Lancet study combined data from multiple past papers to estimate the degree and length of protection after getting COVID-19. The researchers, from the University of Washington’s Institute for Health Metrics and Evaluation, found that infection reduced the risk of reinfection, but that this protection diminished more quickly once omicron arrived in late 2021. (Before the emergence of omicron and its subvariants, there was the original virus followed by variants including alpha, beta and delta.) Protection against severe disease was high for all variants studied.
Drawing on their own data from a study that is not yet published, they also made comparisons to the immunity offered by vaccines. “Although protection from re-infection from all variants wanes over time, our analysis of the available data suggests that the level of protection afforded by previous infection is at least as high, if not higher than that provided by two-dose vaccination using high-quality mRNA vaccines (Moderna and Pfizer-BioNTech),” they wrote.
Citing the study, articles and social media posts have spread stating that immunity from infection is superior to immunity from vaccines, or that “natural immunity offers stronger protection than vaccination against COVID.”
The reality is more complicated.
First, the idea that immunity from infection is superior to immunity from vaccines exaggerates the stated conclusions in the Lancet paper. The data did not show that immunity from infection was superior to immunity from two vaccine doses, simply that it was at least equivalent, Stephen Lim, a professor of health metrics sciences who co-authored the new Lancet study, told us in an email.
Second, the study did not look at “hybrid immunity” from both infection and vaccination, which some evidence suggests is stronger than either immunity from infection or vaccination alone.
Third, COVID-19 disease and vaccination are fundamentally not comparable in certain ways. COVID-19 is a disease that has killed at least 6.8 million people, including more than 1.1 million Americans, and sickened many more. Vaccination is a safe tool people can use to reduce risk of severe disease.
“Vaccines, of course, remain the safest way to acquire immunity, whereas acquiring natural immunity must be weighed against the risks of severe illness and death associated with the initial infection,” Lim said, echoing a similar statement made in his paper.
Lancet Findings on Immunity After Infection
The Lancet paper is a systematic review and meta-analysis, which means the authors searched for previously published studies that measured protection from COVID-19 in people who had been infected and people who had not and then combined data from the papers to estimate protection.
They found 65 studies from 19 countries, concluding that “protection against re-infection was high” when measuring reinfections with the earlier COVID-19 variants: the original virus, as well as the alpha, beta and delta versions. Protection against reinfection with omicron BA.1 — the first omicron variant — was “substantially” lower.
Over time, protection from reinfection decreased for all variants but decreased more quickly with the arrival of omicron. Using data from the 30 studies that included information on time since infection, the authors estimated that at four weeks after infection, protection from the ancestral, alpha and delta variants was around 85%, falling to a little under 79% by 40 weeks after infection. Protection against reinfection with the omicron BA.1 variant was 74% at four weeks and around 36% by 40 weeks.
It makes sense that protection from reinfection would decline with the arrival of omicron, since it was more immune evasive and more transmissible than prior variants. Only a few studies included in the meta-analysis looked at protection against reinfection with omicron subvariants that came after BA.1, and none looked at the currently circulating XBB.1.5, making it more difficult to draw conclusions about current protection.
However, based on data from a small number of studies, protection from reinfection with omicron variants was higher if someone had a prior infection with omicron, rather than a pre-omicron variant.
Protection against hospitalization or death at 40 weeks remained high regardless of variant. Infection reduced risk of severe disease by nearly 89% for omicron BA.1 and a little over 90% for ancestral, alpha and delta.
Vaccination and Infection Both Provide Protection Against Future Disease
The primary focus of the new Lancet paper was to compare protection from past infection versus no past infection, Lim said. He and his colleagues plan to submit a separate paper soon that elaborates on the comparison between vaccines and past infection.
Lim told us that he and his co-authors concluded that past infection was at least as protective as the best mRNA vaccines, not that it was more protective. This is due to uncertainty in their estimates for the protection provided by each, he explained. “Based on the data included in our review, there is insufficient data to definitively state that there is a numerical advantage of past infection against the best mRNA vaccines,” Lim said.
Some posts and articles overstate the weakness of vaccine-induced immunity. A widely shared Defender article, for example, led to a post inaccurately claiming that “#COVID vaxx makes you MORE likely to get COVID.”
As we have written, this is incorrect. The Defender article cites a graph comparing vaccine effectiveness after three vaccine doses versus two doses but incorrectly interprets it as showing vaccine-acquired immunity eventually “became negative.”
The Defender is a publication of Children’s Health Defense, an organization run by Robert F. Kennedy Jr. that has previously spread vaccine misinformation.
Alejandro Balazs, an immunologist at the Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology and Harvard, told us in an email that vaccine effectiveness varies significantly depending on the variants circulating and a person’s particular history of COVID-19, including whether they were infected and when this happened in relation to vaccination. Because of these factors, “discussion of whether natural immunity is better than vaccines requires a level of nuance which is rarely discussed,” he said.
Regardless of which type of immunity is better or more durable, there is evidence that vaccines benefit people who have already had COVID-19.
Lim, Balasz and Daniela Weiskopf, an immunologist at the La Jolla Institute for Immunology, all said that the Lancet researchers didn’t assess immunity in people who have gotten some combination of vaccines and infections.
A review study published in the Lancet Infectious Diseases in January 2023 looked at protection against the omicron variant, comparing hybrid immunity to immunity following vaccination alone or infection alone. Hybrid immunity provided the strongest and most lasting protection against hospital admission or severe disease.
Weiskopf also said that while infection does appear to generally provide protection, there remains a small group of people who do not mount a durable immune response. It is difficult to predict who might fall into that group.
Lim said that people making decisions about primary vaccines and boosters must take into account individuals’ risks and those of their close contacts.
“For example, risk of severe disease increases dramatically with older individuals as well as those with comorbidities, e.g. those who are immunocompromised. Vaccines provide an important immunity boost for these high-risk populations,” Lim said. He added that vaccines are also important for people who have not had COVID-19 before, those who were infected with a variant prior to omicron, and those who regularly spend time with people at high risk.
COVID-19 Vaccines Are Safer Than Infection
Posts and commentators discussing immunity after infection often leave out the dangers of COVID-19 infection, or misleadingly imply that COVID-19 vaccines are unsafe.
Speaking during a segment on Fox News that mentioned the new Lancet paper, Dr. Scott Atlas said people previously infected with COVID-19 “have biological protection that is better, not just equal, better as proven by the data from the vaccine.”
Atlas, a neuroradiologist who was a member of former President Donald Trump’s coronavirus task force and has previously spread misinformation about COVID-19, continued, “The vaccine has side effects. We still don’t have a real, accurate assessment of the side effects even though we’ve had 5 or 6 billion doses. You have to wonder why that is.”
COVID-19 vaccine side effects are mild and temporary in the vast majority of cases, and some people have no side effects. Common side effects include fever, headache, fatigue, muscle pain and pain at the injection site. Vaccine safety monitoring systems have detected only rare cases of serious side effects.
In contrast, COVID-19 infection can result in death or long-term medical issues, including heart and lung problems.
“I do not think that immunity from infection is superior based on the evidence,” Balazs said, adding that there are “considerable risks associated with COVID-19 infection, particularly in vulnerable populations. Side-effects from vaccines are rare as compared to health risks from COVID-19.”
“We know that vaccinations are increasing your antibody levels and your T cell levels without the risk of you getting sick,” Weiskopf said.
Data on Immunity After Infection Are Not New
Many social media posts and articles have focused on the idea that someone — be that the media, government or public health officials, or some unspecified group — has omitted or suppressed information about immunity after infection. Widely shared posts also include “natural immunity” on a long list of topics “they” got wrong and declare “WE WERE RIGHT ABOUT EVERYTHING!”
The idea that infection provides substantial protection from future COVID-19 is not new. Scientists have been publishing the available evidence on immunity following COVID-19 since 2020, although early on there was uncertainty about the duration and reliability of this protection. Major media outlets have covered these findings. Weiskopf pointed out that as a meta-analysis, the new Lancet study itself only draws on previous studies, meaning the data underlying its conclusions were already available.
The National Institutes of Health has promoted research it helped fund looking at immunity after infection, including research that looked into the question of whether previously infected people needed one or two primary COVID-19 vaccine doses. The CDC has also previously reviewed the strengths of immunity after infection, noting the protection afforded by prior infection while also emphasizing the benefits of hybrid immunity.
It’s true that the CDC has not always accounted for past infection in its guidance. Some experts have criticized the agency for this.
But it’s also important to recognize that early on, there was limited data on how protective immunity after infection would be, and other coronaviruses, such as those that cause colds, did not provoke long-lasting protection against reinfection. Given the uncertainties, and the possibility that some subset of people would not be very well protected, health authorities encouraged vaccination even for those who were previously infected.
The agency stated in early 2021, “Due to the severe health risks associated with COVID-19 and the fact that re-infection with COVID-19 is possible, vaccine should be offered to you regardless of whether you already had COVID-19 infection,” explaining that it was unknown how long protection after COVID-19 would last and that immunity can vary from person to person.
And for a while, both vaccination and previous infection were quite good at preventing not just severe disease, but another infection. Then, with the arrival of the delta variant — and even more so with the omicron variant and its subvariants — it became clear that neither vaccination nor previous infection was very protective against infection for very long, although it turned out that protection against severe disease held up well.
By that time, though, accumulating evidence pointed to the benefit of previously infected people getting vaccinated, and a first booster dose looked to be helpful in protecting against omicron, as we wrote in January 2022. Data continue to suggest that an additional shot or two can help boost and broaden the immune response, offering better protection against future variants, although experts say not everyone may need them.
Today, the CDC says, “Getting a COVID-19 vaccination is a safer and more dependable way to build immunity to COVID-19 than getting sick with COVID-19.” The agency now says people “may consider” waiting three months after a positive test or the beginning of symptoms to get their next vaccine dose. (Some experts say for individuals who are young and healthy, it’s better to wait a bit longer than that after infection for a booster.)
“The fact that the guidance evolved over the past three years is clearly a source of frustration for the public, but it reflects the changing nature of the threat and incorporated the best available information at the time,” Balazs said. “With the benefit of hindsight it is easy to criticize public health decisions, but people should consider that the facts on the ground kept changing as the pandemic evolved, so the science changed with it.”
Editor’s note: SciCheck’s articles correcting health misinformation are made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation.
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