My message to RFK Jr.: Think carefully before acting on your new vaccine policy.

The outcome of the U.S. election, with RFK Jr. overseeing public health issues, will bring about a spectacular shift in public health policy. This is a welcome change, as the incompetence, conflicts of interest, and stubbornness of health authorities in the U.S. and beyond are disheartening. However, as a vaccinologist, I am somewhat concerned about the extreme polarization that America is currently experiencing. This polarization now threatens to penetrate even the deepest layers of society, including public health.

For every point of disagreement, the response nowadays seems to need to be black or white. These days, one is either an unconditional advocate of unrestricted vaccination practices or despises every needle that fits on a vaccine syringe. The scientific weighing of pros and cons—depending on the target group, type of vaccine, epidemiological situation, and objective data from relevant studies—seems to no longer be part of the decision-making process for many.

Often, arguments regarding the isolated impact on the individual are overly simplistic. I don’t mean to suggest that we, as a society, should just have to accept that our healthy children—who may never even become exposed to the disease they are being vaccinated against—being injected with substances that could potentially cause serious health issues, even if the latter would only occur on very rare occasions. Rather, I am referring to the general lack of awareness that so-called vaccine-preventable infectious diseases can only be contained through a form of immunity collectively mounted by the population, namely, herd immunity. This has become a topic that neither the so-called pro- nor anti-vaxxers wish to debate, likely because few truly understand its biological implications. I recently pointed out some common misunderstandings regarding this issue:

https://voiceforscienceandsolidarity.substack.com/p/never-ending-misconceptions-about?r=y46t6&utm_campaign=post&utm_medium=web&triedRedirect=true

Herd immunity ensures that the spread of the virus is suppressed to the point where it no longer causes productive infections in individuals who lack protective immunity to the virus. Herd immunity can only be achieved when a large enough portion of the population builds an immune response that protects against productive infection. Such immunity develops spontaneously when, for example, a population is overwhelmed by a pandemic caused by a virus that naturally provokes an acute, self-limiting infection. Such viral infections (e.g., SARS-CoV-2) can spread rapidly through asymptomatic shedding but are usually quickly contained by cytotoxic immune effector cells in individuals who develop symptomatic infection (hence, the self-limiting nature of these infections).

Symptomatically infected individuals are protected from productive infection upon subsequent exposure, thanks to trained innate immunity, which may be combined with a recall of previously induced, virus-neutralizing antibodies (Abs). Consequently, larger portions of the population will eventually have sterilizing immunity after natural infection. In many cases, especially among children and young healthy people, a well-trained first line of immune defense as the sole natural immune response suffices to prevent productive infection upon exposure. This already explains why in a young and healthy population, the level of herd immunity cannot be assessed by measuring the increase in serum titers of (neutralizing) Abs. Such measurement of so-called seroconversion in the population would lead to a serious underestimation of herd immunity. Conversely, when virus spread is controlled by herd immunity, innate immunity will weaken, and neutralizing Ab concentrations in the blood will decrease, reducing herd immunity. This, however, is not a problem as long as the population is not exposed to an external source of the virus, or a sufficient portion of the population possesses an immunological memory of neutralizing Abs. However, individuals who have not previously contracted the disease or didn’t even get infected at all are at risk of becoming ill, or even severely ill, when herd immunity wanes. This is why and how maintaining herd immunity can prevent recurrent epidemics.

Immunizing the immunologically naive portion of the population (e.g., newborns) with live-attenuated vaccines not only strengthens innate immunity but also establishes an immunological memory of adaptive Abs, thereby contributing both to the individual protection of the vaccinated and to maintaining herd immunity in the population. While maintaining herd immunity can prevent recurrent epidemics, it cannot prevent a pandemic caused by a highly divergent viral variant due to the specificity of the Abs produced by previously infection- or vaccine-induced memory B cells. It is therefore not surprising that these live-attenuated vaccines can only be used to prevent epidemics caused by specific viruses that not only provoke acute, self-limiting infections but also have a high degree of genetic stability (e.g., measles, mumps, rubella virus).

I therefore continue to advocate for a new vaccine approach that enables training of broad, non-variant-specific cell-mediated innate immunity to prevent productive infection through sterilizing immunity. Such an immune intervention would not only protect the vaccinated individual from illness but also protect immunologically naive individuals by sufficiently curbing virus transmission within the population to prevent productive infection in these individuals.

I therefore continue to argue that a laissez-faire attitude toward viruses capable of rapidly spreading through entire populations and causing acute, potentially fatal infections is a flawed approach, as it will create gaps in the population's herd immunity. Even in industrialized countries, good general and personal hygiene and adequate sanitary conditions cannot guarantee protection against these viruses, especially when they are also airborne. Large gaps in herd immunity can quickly lead to high infection pressure, where it is even conceivable that the virus could cause severe breakthrough infections in immunologically primed individuals.

There are indeed approaches with the potential to enhance natural, cell-based innate immunity (e.g., Natural Killer cell vaccines) in a way that provides broad protection against a multitude of respiratory viruses and other infectious agents (or even non-infectious agents like allergens). However, it goes without saying that the vaccine industry is not interested in developing such broad-spectrum vaccines as deploying immune interventions that can prevent or treat multiple diseases/infections simultaneously does not represent a lucrative objective. On the other hand, the notion that we should throw out the baby with the bathwater and focus solely on personalized vaccinology, even for infectious diseases that manifest at a population level, is at best short-sighted.