The authorized COVID-19 vaccines have been found to be safe and effective in clinical trials and in real-world conditions. Out of more than 220 million doses administered so far and clinical trials with thousands of participants, there is no evidence showing that vaccinating those with previous SARS-CoV-2 infections could be unsafe. 

On the contrary, increasingly growing evidence shows one dose of the vaccine benefits individuals who’ve recovered from the infection, boosting their immune response and providing them with full protection for a period of time. 

“Our study and several other studies show that there is a benefit, immunologically … in people who were previously infected,” E. John Wherry, director of the University of Pennsylvania’s Institute for Immunology, told in a phone interview.

Yet a number of viral posts question the need of vaccinating those who’ve already recovered from COVID-19, and one of them, published by Robert F. Kennedy Jr.’s anti-vaccination organization, falsely claims it “could potentially cause harm, or even death.” 

Researchers told that is not what the evidence is showing. 

“There’s no indication that vaccinating people who had previously had COVID is resulting in an increased risk of adverse events,” Wherry said. 

Wherry, who is one of the lead authors of a study looking at the immune responses to the mRNA vaccines in individuals with and without previous infections, said people who recover from the disease show different levels of antibodies created by the immune system to identify and neutralize the virus. The vaccines, he said, improved the immunity response in individuals by raising the levels of neutralizing antibodies in those who’ve been infected. 

“Some people actually have fairly low antibody responses that are not sufficient to neutralize the virus, especially variant viruses. When you vaccinate them uniformly, you get high antibody titers [measurements] and high neutralization titers, so there’s an improvement in at least one of the key metrics of immunity following vaccination,” he said.

According to guidance by the Centers for Disease Control and Prevention, people who’ve already had COVID-19 should be vaccinated anyway because “experts do not yet know how long” they are protected from getting sick again. Those who’ve gotten the disease get some protection by building what’s called natural immunity. And although available evidence shows that reinfection is uncommon in the months following the first infection, the CDC says that may vary over time. 

“Available data suggest that previously infected individuals can be at risk of COVID-19 (i.e., reinfection) and could benefit from vaccination. Furthermore, data suggest that the safety profile of COVID-19 vaccines in previously infected individuals is just as favorable as in previously uninfected individuals,” a spokesperson for the U.S. Food and Drug Administration told us in an email. 

Up until now, the passive and active surveillance systems set up to monitor the safety of the COVID-19 vaccines have only found rare adverse events associated with the vaccines.

A small number of people (2 to 5 people per million vaccinated) have reported a severe allergic reaction called anaphylaxis. And the CDC and the FDA are studying a small number of cases of people who experienced a rare and severe type of blood clot with low platelets after getting the Johnson & Johnson vaccine. As a result, the agencies recommended a pause in the use of this product. On April 23, a CDC panel of advisers recommended the pause be lifted. 

No evidence of risk for previously infected individuals 

In a blog post on The Defender, a website owned by R.F.K. Jr.’s organization, Children’s Health Defense, a freelance reporter writes that there’s no science supporting the need of vaccinating people who have recovered from COVID-19. “There’s a potential risk of harm, including death, in vaccinating those who’ve already had the disease or were recently infected,” the post claimed. 

Researchers don’t agree, including one quoted by The Defender. 

Dr. Colleen Kelley, an associate professor of medicine and epidemiology at Emory University School of Medicine and the principal investigator for Moderna’s and Novavax’s phase 3 vaccine trials at Emory, is quoted by The Defender as saying people with previous infection get “harsher side effects” after vaccination. Her remarks came from a HuffPost article in March.

In a phone interview, Kelley told us that tolerable side effects are expected, and not always present. In the Moderna trials, “there did not appear to be an increased rate of side effects among people who were antibody positive when they were vaccinated,” she said.  

“There is absolutely no evidence that there is any harm for people to be vaccinated, who have previously had COVID disease,” Kelley said. 

The Defender’s claims are mostly based on statements by Dr. Hooman Noorchashm, a former assistant professor of surgery at the University of Pennsylvania School of Medicine, who has been warning health officials, vaccine manufacturers and more recently university leaders of the potential danger of vaccinating people who have recently been infected with the novel coronavirus. 

Noorchashm has been voicing his arguments widely, including on Fox News’ “Tucker Carlson Today“ and The Defender podcast. But he admits they are based on “a ‘prognostication’ in that I have put it forth in the absence of clear ‘evidence’ of it being a material risk.” 

Based on previous studies not related to the COVID-19 pandemic, Noorchashm argues that antigens of SARS-CoV-2 remain in the tissues of someone who’s been infected for some time after they’ve recovered. The vaccine, he says, reactivates the immune response, targeting the tissues where these antigens remain, causing further inflammation and damage, including to the vascular endothelium, the thin tissue that lines the heart and blood vessels. 

“Most pertinently, when viral antigens are present in the vascular endothelium or other layers of the blood vessel, and especially in elderly and frail with cardiovascular disease, the antigen specific immune response incited by the vaccine is almost certain to do damage to the vascular endothelium,” he said in a Jan. 26 letter sent to FDA officials and Pfizer executives. “Such vaccine directed endothelial damage is certain to cause blood clot formation with the potential for major thromboembolic complications, at least in a subset of such patients.” 

In a phone interview with, Noorchashm explained that all medical treatments, including vaccines, have some complications. And if those complications happen when a treatment is avoidable — in this case, he says, vaccinating those who’ve recently been infected — then that’s potentially harmful.

His recommendation is to test people’s antibodies before vaccination and to delay vaccination for approximately eight months after infection. He and his wife, a physician who died in 2017, fought for years to ban a tool used to remove uterine fibroids, after the procedure spread cancer into his wife’s abdomen. 

Dr. Steven Varga, a professor of microbiology and immunology at the University of Iowa whose lab studies immunopathology in respiratory virus infections, told us he’s not aware of any scientific data that demonstrates that viral antigens persist long after the SARS-CoV-2 infection has gone away. And if there were, he says, there would likely be insufficient levels to drive such a robust immune response to cause the damage Noorchashm suggests. 

“Generally, once the virus is cleared, there can be some viral antigen that persists in various locations, so it is possible there could be some in the endothelium,” Varga said. “Again, I’m not aware of any studies that have shown that to be the case. But even if there were small amounts of viral antigen, generally that shouldn’t be enough viral antigen to induce the type of damage that would need to occur to have the kind of more severe outcome.” 

Dr. Donna Farber, a professor of microbiology and immunology at Columbia University focused on immunological memory, told us Noorchashm’s prognostication is not consistent with the data. 

“The data are that the virus is cleared from the lungs, the virus is cleared from the upper respiratory tract. And so if there’s no virus, there’s no antigen,” Farber, who recently published a study on the immune response to COVID-19 in the lungs, said in a phone interview. 

Farber added that the protective immunity provided by the vaccine, neutralizing antibodies, do not cause the sort of harm Noorchashm is talking about. That could happen, she says as an example, if there was a virus hidden in cells and then a patient is given cytotoxic T cells, a type of immune cell that can kill infected cells or cancer cells. 

“But the chance of that happening in a vaccine — and for a vaccine that’s really targeting neutralizing antibodies and not, you know, the sort of a killer T cell response —  it’s just inconsistent with the science,” she said. 

Farber also said for most pathogens, our immune system requires repeated exposure to get protection over time. That’s why people get a vaccine for influenza every year, she said, regardless if they’ve been exposed to the virus or not. 

“Seeing an antigen again and again, isn’t bad for you. It’s what we do all the time. And it’s what our immune system has evolved to do. And that’s how it generates its best memory,” she said.

This column was edited for space. See the whole column at

Clarification, April 27: Although nothing in the article indicates that Dr. Noorchashm is a member of an anti-vaccination group, Dr. Noorchashm requested FactCheck to add that he is not anti-vaccine. He said he has been vaccinated against COVID-19.  

 SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over our editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate information about COVID-19 and vaccines, while decreasing the impact of misinformation.

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