Background
It has been known since the Athenian plague of 430 BC that recovered individuals are protected when re-exposed to an infectious disease, at least for some amount of time. This is called infection-acquired immunity or natural immunity, as opposed to vaccine-acquired immunity. Protection may be absolute or partial, resulting in sterilizing immunity that prevents reinfection or in non-sterilizing immunity that decreases severity of disease if reinfected. With few individuals becoming reinfected early in the pandemic, it was obvious that most recovered individuals mounted robust and protective immune responses. Although sterilizing immunity may wane over time, protection from severe disease post-COVID-19 infection is, so far, long-lasting, similar to other coronaviruses that cause common colds.
The issue of infection-acquired immunity was and is at the core of many disputed pandemic policies. Without durable infection-acquired immunity, herd immunity[1] cannot be reached, there would be no effective vaccines, and high-risk individuals would have to be sheltered forever unless the virus was eradicated. However, evidence existed early on that prior infection conferred durable protective immunity in the case of SARS-CoV2, meaning that efforts should have been aimed at protecting high-risk individuals until sufficient immunity could be reached in the population through a combination of infection-acquired and vaccine-acquired immunity.
Another reason that denial of natural immunity led to misguided COVID-19 policies is that vaccines were assumed to have superior immunity compared to natural infection, an assumption that led to widespread vaccine mandates even in previously infected people. Prior infection and vaccines both provide a form of immunity. Acknowledgement of infection-acquired immunity is not an argument against vaccines. For example, the purpose of the measles vaccine is to prevent measles, but those who have already had measles do not need the vaccine.
Denial and Questioning of Infection-Acquired Immunity
Contrary to vaccine-acquired immunity, which was overemphasized, infection-acquired immunity was consistently downplayed during the pandemic.
In October 2020, a widely circulated Memorandum [2] published in The Lancet, a top British medical journal, questioned infection-acquired immunity. It stated that “there is no evidence for lasting protective immunity to SARS-CoV-2 following natural infection”, claiming “scientific consensus” for this view. The Memorandum was co-authored by several senior US scientists, including Drs. Marc Lipsitch (Harvard), Ali Nouri[3] (president, American Federation of Scientists) and Rochelle Walensky[4] (Harvard). With extremely few reinfections at the time, clear evidence for the existence of infection-acquired immunity, and despite what we know about other coronaviruses, on what basis did these scientists question that infection with SARS-CoV-2 provided lasting protection from severe disease for recovered individuals and, early on, from reinfection? What was the rationale for The Lancet editor-in-chief, Dr. Richard Horton’s[5], decision to publish the Lancet Memorandum that questioned infection-acquired immunity after SARS-CoV-2 infection without citing supporting data and which ran in opposition to well established immunologic principles?
In the same week as he co-authored the Lancet Memorandum, the president of the American Federation of Scientists, Dr. Ali Nouri, published an article in Scientific American arguing for stronger efforts to combat COVID-19 misinformation. Why did Scientific American publish a piece arguing for combatting COVID-19 misinformation authored by a scientist questioning infection-acquired immunity?
In 2020, prior to availability of COVID-19 vaccines, there was very little information about infection-acquired immunity on the CDC.gov website. This was in spite of much robust international data already being available. One exception was the page discussing antibody tests: “Having antibodies to the virus that causes COVID-19 may provide protection from getting infected with the virus again. If it does, we do not know how much protection the antibodies may provide or how long this protection may last.” Why did the CDC downplay infection-acquired immunity, despite robust evidence for it?
In the summer of 2021, all references on the CDC.gov website to immunity after infection with SARS-CoV-2 were removed. Vaccination was recommended even in recovered individuals: “Get vaccinated regardless of whether you already had COVID-19. Studies have shown that vaccination provides a strong boost in protection in people who have recovered from COVID-19.” With no evidence cited in support of this statement, what was the evidence supporting the CDC’s claim when the prior six months had produced several additional studies showing that infection-acquired immunity was protective, robust, and long-lasting?
On August 6, 2021, the CDC published a Kentucky-based study as an MMWR early release article. Among people with infection-acquired immunity from 2020, the study reported that people who were subsequently vaccinated were less likely to test positive for COVID-19 than those with only infection-acquired immunity. However, the study did not evaluate differences in hospitalization and death or even symptomatic disease. Why did CDC Director Rochelle Walensky cite this study to support her statement that “if you have had COVID-19 before, please still get vaccinated” ?
By October 2021, there was substantial evidence of robust immunity in persons with a history of only mild or asymptomatic infections. Despite this, the CDC claimed that “there are insufficient data to extend the findings related to infection-induced immunity at this time to persons with very mild or asymptomatic infection or children”. In light of the scientific evidence, why did the CDC claim that individuals with immunity after recovery remained unprotected from severe reinfection? Why was substantial scientific literature on this topic ignored? Who was involved in those discussions and decisions?
The concept of infection-acquired immunity is well understood by the public, and has been for hundreds of years. By questioning this well-known concept, how much damage did the CDC, other public health officials and public health scientists do to public health’s credibility, and to vaccine confidence and adherence to mitigation policies?
Through the CDC Foundation, the CDC receives funding from pharmaceutical companies and other organizations. Over the years, has it received donations from vaccine-related interests such as Astra-Zeneca, Johnson & Johnson, Pfizer, Moderna, the GAVI Alliance and/or the Gates Foundation? Did CDC decision makers have conflicts of interest in questioning the role of infection-acquired immunity in protection from severe COVID-19?
Infection-Acquired Immunity in the Workforce
Infection control is very important in hospitals and nursing homes in order to protect elderly frail patients and others with weakened immune systems. Minimizing risk of infection by hospital and nursing home staff is important.
When vaccines became available, hospital and nursing home staff were prioritized to reduce transmission risk to their elderly high-risk patients and residents. Before vaccines were available, COVID-19 risk to older high-risk nursing home residents and hospital patients could be reduced if patients were cared for by staff with infection-acquired immunity.
Why did hospital and nursing homes not pursue such focused protection of the most vulnerable? Why did they not try to hire staff with infection-acquired immunity? Why was this not recommended by the CDC?
Since infection-acquired immunity offered superior protection compared to vaccine-acquired immunity, why did hospitals fire rather than hire unvaccinated nurses, physicians and other staff who had infection-acquired immunity? Why did hospitals implement vaccine mandates without providing exceptions for staff with infection acquired immunity?
After firing many unvaccinated nurses and physicians, some hospitals experienced severe staff shortages in late 2021 and into 2022, many which persist today. How did this affect the quality of healthcare? How many patients did not receive healthcare because of this? What did governors and state health departments do to avoid these self-imposed problems? Has there been any discussions of or plans to compensate staff who lost their jobs due to vaccine mandates?
Infection-Acquired vs Vaccine-Acquired Immunity
Vaccines are designed to mimic the immune response from a disease while avoiding the risks involved with being infected. Individuals are capable of understanding risks when given accurate information and acknowledging that infection-acquired immunity is superior to vaccine-acquired immunity is not equivalent to promoting infection over vaccination. On its website, the CDC wrote that “the risk of severe illness and death from COVID-19 far outweighs any benefits of natural immunity.” However, for people that have already survived an infection, the relevant question is whether they have acquired immunity, which they do in the vast majority of cases. For people without a prior COVID-19 infection, the relevant comparison is vaccine efficacy versus adverse reactions. Did the CDC damage vaccine confidence when they conflated these two issues?
The CDC Kentucky study from August 2021 did not evaluate symptomatic disease, hospitalizations or death, but it showed fewer positive COVID-19 tests in people who had combined immunity (from both Covid-19 infection and vaccination), compared to COVID-19 infection alone (both were very low, however). Since all participants in the study had infection-acquired immunity, why did the title of the CDC press release for this study falsely claim that “Vaccination Offers Higher Protection than Previous COVID-19 Infection.”? That question was not evaluated in the Kentucky study. Why did NIH director Francis Collins use this study to falsely claim that “it was more than two-fold better from the people who had the vaccine, in terms of protection, than people who had had the natural infection”?
It is important to know if the vaccines can provide the same or similar level of immunity as infection-acquired immunity. Early important studies on that topic were conducted in Israel, Sweden and Qatar. Why did the CDC or NIH not fund or conduct such studies in the United States until January 2022? Why were the results of Israeli and Swedish studies largely ignored by public health authorities in the United States?
In September 2021, why did Health and Human Services Secretary Xavier Becerra refuse to acknowledge that infection-acquired immunity is superior to vaccine-induced immunity?
In October 2021, CDC released a methodologically flawed study claiming that vaccine-induced immunity was 5.3 times more effective than infection-acquired immunity. Did CDC officials know about high quality studies from other countries that showed opposite results? In the CDC press release about the study, why did Dr. Rochelle Walensky falsely claim that “we now have additional evidence that reaffirms the importance of COVID-19 vaccines, even if you have had prior infection”?
In January 2022, the CDC published a study using statewide data from New York and California confirming that infection-acquired immunity was superior to vaccine induced immunity. What was the impetus for this new study? After this study was published, and after the methodological flaws in the previous CDC study were pointed out by various scientists, why did the CDC not retract the prior flawed study? To date, this newer article has not been cited in any CDC press release and is not mentioned by the CDC on any of its informational web pages. Why did CDC not publicize this study as much as their prior flawed study?
In a September 2021 Munk Debate, Dr. Paul Offit argued for general vaccine mandates. In a subsequent January 2022 podcast, he described a meeting where CDC Director Rochelle Walensky, NIH Director Francis Collins, NIAID Director Anthony Fauci, and surgeon general Vivek Murthy, asked the advice from four experts whether “natural immunity should count as a vaccine”. The outcome of the meeting was that it should not. In the podcast Dr. Offit acknowledged that infection-acquired immunity is strong “as you would expect, it is true for every other virus … except the flu … [and that] you’ve been vaccinated essentially”. He then described the decision as “probably more bureaucratic than anything else.” Is Dr. Offitt correct that the denial of infection-acquired immunity was a bureaucratic rather than a science-based decision? Were vaccine mandates also a bureaucratic rather than a science-based decision? Who were the other three “experts” consulted on this matter and how did they vote? If important public health decisions are taken for bureaucratic rather than scientific reasons, how does that affect the public's trust in public health?
Herd Immunity: Policy Implications and Messaging Failures
The term “herd immunity” refers to a threshold where a sufficient portion of people in a population have acquired immune protection to a specific infectious agent, either through recovery from infection or vaccination, so that the virus can no longer circulate at epidemic levels. At that time, there is some protection for those who have not yet acquired immunity, protecting high-risk individuals from severe disease and death. It does not mean that the disease has been eradicated. On the contrary, once herd immunity is reached, an endemic equilibrium stage is reached in which the infection rate is related to the rate of waning immunity and the birth of susceptible individuals. Because of seasonality, it is possible to reach herd immunity during summer months with the epidemic reemerging when seasonality raises the reproductive number during the fall or winter.
For some infectious diseases such as measles, recovery or vaccination results in lifelong protection. For others, such as common cold coronaviruses, immune protection against reinfection (usually mild) is not long lasting. This does not mean that herd immunity is invalid, but rather that periodic mild reinfections or vaccination will restore community protection while protection from severe disease is maintained.
Public comments from health officials in the U.S. have demonstrated that this concept was poorly understood at the highest levels during the COVID-19 pandemic. In a 2022 paper by Dr. Anthony Fauci and colleagues, “The Concept of Classical Herd Immunity May Not Apply to COVID-19”, the authors questioned whether the natural and well-established phenomenon of herd immunity applies to SARS-CoV-2, due to waning of immunity and the rate of mutation. However, herd immunity limits transmission and protects against serious disease outcomes, even as sterilizing immunity wanes. Like other pandemic viruses, the SARS-CoV-2 virus becomes endemic as a result of sufficient population immunity. In 2022, former White House Coronavirus Task Force Response Coordinator Dr. Deborah Birx testified to Congress that “herd immunity is not usually discussed as it comes to humans. Herd immunity comes out of vaccinating your cows and your pigs…So that’s how herd immunity is discussed. We don’t discuss that usually about humans.” A 2022 search for “herd immunity humans” on PubMed generated over 2,900 scientific articles on the topic. Former CDC Director Robert Redfield has stated that: “I thought for COVID-19, that there is no herd immunity”.
Why do three of the architects of the U.S. government’s COVID-19 policy seem to be questioning such an important epidemiological concept? How did their beliefs about herd immunity affect the nation’s COVID-19 response? Why did they question whether herd immunity applies to SARS-CoV-2, at least for severe disease?
Did any or all of them consult with infectious disease epidemiologists who specifically study this topic?
Footnotes
[1] The term “herd immunity” refers to a threshold where a sufficient portion of people in a population have acquired immune protection against a specific infectious agent, either through recovery from infection or vaccination, so that the virus can no longer circulate at epidemic levels. It does not refer to eradication.
[2] The authors called it the John Snow Memorandum, but John Snow was a great epidemiologist and it is inappropriate to connect his name to this document. Hence, we will call it the Lancet Memorandum.
[3] Dr. Nouri was later appointed as the Assistant Secretary in the Department of Energy.
[4] Dr. Walensky was later appointed as the Director of the Centers for Disease Control and Prevention.
[5] This is the same editor who published the controversial 2020 Lancet letter denouncing “rumours and misinformation around its origins” and condemning “conspiracy theories suggesting that COVID-19 does not have a natural origin”.