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Bred Weinstein claimed in an interview on Triggernometry:

Why on earth are we vaccinating people who had COVID? They will get the very same immunity. There's no evidence their immunity gets better for vaccinating them. We are exposing those people to the risks of these vaccines for no benefit. It doesn't make anybody else immune. It doesn't get us any closer to herd immunity.

Is there a clinical benefit (less change of infecting others/hospitalization/death) for vaccinating people who already have had COVID-19?

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Assuming you're using the past tense correctly, indicating the subject has recovered from the infection, the CDC says so:

Yes, you should be vaccinated regardless of whether you already had COVID-19. That’s because experts do not yet know how long you are protected from getting sick again after recovering from COVID-19. Even if you have already recovered from COVID-19, it is possible—although rare—that you could be infected with the virus that causes COVID-19 again. Studies have shown that vaccination provides a strong boost in protection in people who have recovered from COVID-19. Learn more about why getting vaccinated is a safer way to build protection than getting infected.

If you were treated for COVID-19 with monoclonal antibodies or convalescent plasma, you should wait 90 days before getting a COVID-19 vaccine. Talk to your doctor if you are unsure what treatments you received or if you have more questions about getting a COVID-19 vaccine.

If you or your child has a history of multisystem inflammatory syndrome in adults or children (MIS-A or MIS-C), consider delaying vaccination until you or your child have recovered from being sick and for 90 days after the date of diagnosis of MIS-A or MIS-C. Learn more about the clinical considerations people with a history of multisystem MIS-C or MIS-A.

Experts are still learning more about how long vaccines protect against COVID-19. CDC will keep the public informed as new evidence becomes available.

https://www.cdc.gov/coronavirus/2019-ncov/vaccines/faq.html

The WHO appears to agree:

Take whatever vaccine is made available to you first, even if you have already had COVID-19. It is important to be vaccinated as soon as possible once it’s your turn and not wait. Approved COVID-19 vaccines provide a high degree of protection against getting seriously ill and dying from the disease, although no vaccine is 100% protective.

https://www.who.int/emergencies/diseases/novel-coronavirus-2019/covid-19-vaccines/advice

The NIH suggests the same, but mentions a caveat (now obsolete in the US, as we have more doses than people who want them):

Conclusions: Prior infection in patients with COVID-19 was highly protective against reinfection and symptomatic disease. This protection increased over time, suggesting that viral shedding or ongoing immune response may persist beyond 90 days and may not represent true reinfection. As vaccine supply is limited, patients with known history of COVID-19 could delay early vaccination to allow for the most vulnerable to access the vaccine and slow transmission.

https://pubmed.ncbi.nlm.nih.gov/33718968/

One study reported widely (but I'm unsure of its peer review status, and the sample size wasn't that big) even adds more optimism:

If you have recovered from coronavirus and confused about whether to get the vaccine or not, here is the answer. If people who recovered get even one dose of the vaccine, they are as safe as or even more than people who got 2 doses. This study has been published in Infectious Disease Journal.

On the basis of a study conducted at AIG Hospital, Hyderabad, the researchers claim that even a single dose gives a lot of protection to people who have recovered from COVID-19. The hospital has done a study on 260 health care workers. All of them had received a single dose of the Covishield vaccine between January 16 and February 5. The study was to see how much immunity the memory cells can produce when there is a disease.

The results revealed that in people who had been infected with COVID-19 before getting the vaccine, a lot of antibodies were produced in them from a single dose. Whereas in those who never had the infection, antibodies were less. Memory cells also created more immunity in such people.

https://www.dnaindia.com/india/report-one-dose-of-vaccine-enough-for-those-who-recovered-from-covid-19-study-2895310

That study was done in India, and is mostly reported in Indian-targeted news outlets.

Although the consensus is yes, a large unknown is the length of time either type of immunity will last. However, preliminary reports suggest that vaccine immunity may be better at combatting variants than natural immunity.

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    On skeptics we generally believe in Evidence-based medicine and not Authority-based medicine. What the CDC, NIH or WHO say is irrlevant. What counts is what scientific papers say. – Christian Jun 21 at 23:40
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    To the best of my knowledge, neither the duration of protection nor the effectiveness on variants has been firmly established through data, although both are currently being studied. From a behavioral standpoint, without firm and extensive data, we have only a consensus of speculation, which is what the above sources reflect. If I find a credible, peer-reviewed study, I'll update the answer, but consensus of authority is the best we have so far AFAIK. – Cristobol Polychronopolis Jun 22 at 12:14
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    "what the CDC, NIH or WHO say is irrelevant" - man, what an unfortunate state of affairs. – 0xDBFB7 Jun 26 at 14:35
  • @0xDBFB7 Do you think the Royal Society should end their 'Nullius in verba' motto, because we discovered that argument by authority is much better then their tradition of reasoning? – Christian Jun 28 at 19:29
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While not evidence of clinical benefit, there is evidence that vaccination could boost immunity against variants.

The abstract of https://science.sciencemag.org/content/early/2021/03/24/science.abg9175

Emerging SARS-CoV-2 variants have raised concerns about resistance to neutralizing antibodies elicited by previous infection or vaccination. We examined whether sera from recovered and naïve donors collected prior to, and following immunizations with existing mRNA vaccines, could neutralize the Wuhan-Hu-1 and B.1.351 variants. Pre-vaccination sera from recovered donors neutralized Wuhan-Hu-1 and sporadically neutralized B.1.351, but a single immunization boosted neutralizing titers against all variants and SARS-CoV-1 by up to 1000-fold. Neutralization was due to antibodies targeting the receptor binding domain and was not boosted by a second immunization. Immunization of naïve donors also elicited cross-neutralizing responses, but at lower titers. Our study highlights the importance of vaccinating both uninfected and previously infected persons to elicit cross-variant neutralizing antibodies.

This was linked to by this article talking about Rand Paul's claims that people who were previously infected don't need to be vaccinated. The article isn't able to directly refute the claim, but is able to offer some caveats:

First, though natural immunity appears to be very effective against the current dominant U.S. variant (known as alpha), it also appears weaker than vaccine immunity against some of the variants circulating, such as the delta variant, first detected in India. That means if those variants eventually become dominant in the U.S., people relying on natural immunity would be less protected than those who are vaccinated.

Second, there is a lack of data about whether natural immunity prevents asymptomatic transmission and infection. Several other studies, though, show vaccines do.

Third, Crotty said his studies have shown that levels of natural immunity can vary widely in individuals. His team even found a hundredfold difference in the number of immune cells among people.

“If you thought about the immune system as a basketball game and you thought about that as a team scoring 1 point, and another team scoring 100 points, that's a big difference," said Crotty. “We're not so confident that people at the low end of immunity levels would be as protected against covid-19."

But those who receive a vaccine shot have a much more consistent number of immune cells, since everyone receives the same dose amount, said Crotty.

Again these are not direct evidence of clinical benefit, but they do counter the claim that "there's no evidence their immunity gets better for vaccinating them".

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  • Note that this 'evidence' is based entirely on the theoretical assumption that it all hangs on the antibodies and not much more. Which of those, where, how long? IgA, IgM, IgG? Against S (vaccines have that), M, N, other ORFs (no vaccine offers that). How are innate immune system, complement system, T-&B-cells, etc affected? Hard evidence of benefit would show that reinfections occur in concerning numbers (not seen so far, the opposite), and that shots really prevent that (also not seen so far). – LangLаngС Jun 26 at 12:44
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    @LangLаngС If we don't have the data yet, we make do. I don't think there's enough data on breakthrough infections in people who have had both Covid-19 and vaccine in that order, or enough time to gather statistically significant amounts of data. We do know breakthrough infections are less common after vaccination than reinfections are after recovery, particularly with variants, but although that doesn't prove the effectiveness of the combination, it hints strongly that vaccination after infection could improve immunity. Sometimes science involves educated guessing until the numbers are in. – Cristobol Polychronopolis Jun 28 at 19:13
  • Another article that I might incorporate into my answer at some point: yahoo.com/news/delta-variant-makes-even-more-122951183.html – Rob Watts Jul 13 at 16:29
  • Another one abcnews.go.com/Health/… – Rob Watts Jul 20 at 19:26

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