Israeli study finds vaccine hesitancy predicts future COVID-19 vaccine side effects
While the production of COVID vaccines could have been the “light at the end of the pandemic tunnel”, this outcome was hampered at critical stages by vaccine hesitancy from the public.
A COVID-19 vaccination is administered at a Maccabi Healthcare Services vaccination centre in Modi’in, on Dec. 24, 2020. Photo by Yossi Aloni/Flash90.
Even before the outbreak of COVID-19, the World Health Organization considered vaccine hesitancy to be one of the ten global threats to public health. WHO defines this phenomenon as “the reluctance or refusal to vaccinate despite the availability of vaccines.”
Vaccine hesitancy should not be confused with antivax stances. Hesitancy generally stems from a person weighing the pros and cons, while the anti-vac stance reflects harder ideological, religious or political opposition. But both are fueled by inaccurate or exaggerated reports of vaccine side effects.
However, the precise relationship between vaccine hesitancy and COVID-19 vaccination side effects has not previously been explored in vaccinated persons — until now.
Researchers at Bar Ilan University in Ramat Gan and Ariel University in Ariel examined a fundamental question: Do the side effects of a previous dose predict hesitancy towards a later dose? Or, does one’s hesitancy towards an earlier dose predict subsequent side effects from a follow-up vaccination later on? This is known as the “nocebo effect,” which describes a situation where a negative result comes from taking medicine because the patient simply believes it will cause harm.
That’s the opposite of the better-known “placebo effect” in which a beneficial outcome from the medicine takes place because the patient believed it would happen.
They found that hesitancy indeed predicted subsequent side effects.
The team’s peer-reviewed study was published in Scientific Reports on Monday. The researchers studied 750 adults — all older adults because they have a high vaccination rate coupled with low side effects. This made the detection of nocebo effects more challenging, explained the lead researcher, Prof. Yaakov Hoffman, of Bar Ilan’s Interdisciplinary Department of Social Sciences.
The researchers assessed vaccine hesitancy and side effects at two different time points — after the second vaccination dose and six months later after a booster dose.
They also found that the nocebo effect in females is more impacted by previous experience. The link between previous side effects and current side effects was twice as large in females versus males.
Professor Hoffman stressed that the findings are more than about “mind over matter,” but can also shed light for health authorities organising future vaccination campaigns, which are typically geared towards the unvaccinated.
“Public health messaging may, for example, be less suited to those who received a vaccination dose and have electively chosen to discontinue vaccination. In the United States alone, there are over 150 million such persons,” Hoffman said.
The study’s co-author, Prof. Menachem Ben-Ezra of Ariel University, elaborated, saying, “For such persons messaging focused on general vaccination safety may be less applicable to partially-vaccinated individuals who have first-hand experience with vaccine side effects and electively chose to discontinue vaccination. Rather differentiated public health messaging is required.”
