A recent preprint co-authored by the U.S. Centers for Disease Control and Prevention’s (CDC) U.S. Flu Vaccine Effectiveness Network Investigators finds that repeat annual influenza vaccines are associated with an increased risk of influenza infection.
The preprint authors initially wondered if vaccination timing and influenza infections in prior seasons may have contributed to repeat vaccinees’ increased risk of infection.
However, they concluded these factors “cannot fully explain the increased infection risk in repeat vaccinees compared with non-repeat vaccinees.”
Repeat Vaccinees More Likely to Contract 1 Type of Flu
The study followed patients who had presented themselves with respiratory diseases at one of the designated clinics between the 2011 and 2019 seasons. Over 55,000 clinical visits were analyzed, and vaccine status was further examined.
Repeat vaccinees, when compared against non-repeat vaccinees, had a 10 percent increased risk of contracting the influenza type A H3N2 virus but not for influenza type B and influenza type A H1N1 variants.
Those who contracted influenza in prior seasons were more protected against infection if the current circulating variant was of the same subtype.
While repeat vaccinees tended to get vaccinated around a week earlier than non-repeat vaccinees, and the unvaccinated who became infected the prior season did tend to get vaccinated the following season, the authors found that neither factor significantly changed the estimates on the effects of repeat vaccination.
An Ongoing Dilemma
Increased risk of influenza infection among the repeat vaccinated is a phenomenon commonly observed for decades.
As early as the 1970s, studies have signaled that repeat influenza vaccination was linked to reduced vaccine protection.
Similarly, a 2015 Canadian study found that the vaccine provided 43 percent protection among the unvaccinated, while those vaccinated the prior season had an immunity of -15 percent, meaning they were at a greater risk of infection than before.
The phenomenon has long troubled researchers.
A popular theory is the concept of original antigenic sin, meaning that regardless of what virus we encounter, the body is forever biased to respond to newer viral strains the same way it responded to the initial infection.
“Our immune systems react most strongly to the viral strains we encountered in our childhoods … According to the OAS [original antigenic sin] theory, no matter how many flu vaccines or COVID boosters we receive, our bodies would stubbornly insist on churning out tired antibodies against a bygone strain of a virus,” immunologist Gabriel D. Victora of Rockefeller University wrote in an article.
Furthermore, repeat vaccinations against the same virus have been shown to diminish the body’s antibody response.
A study published in Nature Communications found that people vaccinated with the same formulation for two consecutive years developed antibodies that are less effective at binding to and clearing viral components when they become infected—despite the viral strain being similar between those years.
Other studies contradict these findings.
Authors of a 2022 study published in The Lancet Respiratory Medicine found that “although vaccination in the previous year attenuates vaccine effectiveness, vaccination in two consecutive years provides better protection than does no vaccination.”
Natural immunity obtained by contracting an infection is generally suggested to be more effective than the short-term immunity gained from influenza vaccines, according to many experts.
The Nonspecific Effects of Vaccines
Biologist Alberto Rubio-Casillas at the University of Guadalajara told The Epoch Times in an email that different vaccines cause different nonspecific effects.
“That is, they not only prevent the vaccine-targeted disease but also reduce mortality from other infections. Vaccines apparently train the immune system in ways that reduce or enhance susceptibility to unrelated infections,” he said.
“All live-attenuated vaccines examined so far, including BCG (Bacillus Calmette-Guérin), measles virus, and oral polio vaccine (OPV), have beneficial nonspecific effects ... On the contrary, non-live vaccines induce negative nonspecific effects.”
Contrastingly, some studies have suggested that influenza vaccinations may also confer immunity against respiratory syncytial viruses.
Most authorized influenza vaccines now are non-live vaccines.
Live vaccines tend to generate longer and more effective immunity. However, they also tend to cause stronger immunological reactions that may not be effectively cleared by immunocompromised people or those with chronic health problems.
