COVID-19 Boosters Linked to More Illness and Absenteeism in Health Care Workers

A new peer-reviewed Swiss study has found that recent COVID-19 booster shots were linked to higher short-term illness risk and absenteeism among health care workers, raising questions about he benefits of universal booster campaigns, particularly in populations at low risk for COVID complications. The cohort study was published on Aug. 9, 2025 in the journal Communications Medicine. It tracked 1,745 health care workers across nine health care networks between November 2023 and May 2024 to determine whether booster status influenced the rate of influenza-like illness (ILI) and the number of workdays lost.¹

The results of the study showed that health care workers who had received a recent SARS-CoV-2 booster were more likely to report ILI symptoms and take sick leave than those who did not receive a COVID booster shot. The group of participants who did not receive a COVID booster shot included unvaccinated individuals, who, in this study, experienced fewer illness episodes and missed fewer workdays than their recently boosted peers.

Conversely, the study notes that recipients of the seasonal influenza vaccine experienced fewer symptoms and missed fewer days of work, suggesting that the composition and immunological effects of the novel mRNA COVID shots may affect the health of individuals differently than traditional influenza vaccines. While flu shots can also cause side effects that resemble influenza itself, such as fever, fatigue, or muscle aches, the data in this study showed that flu shots were still associated with fewer illness episodes and less absenteeism overall compared to those who got COVID booster shots.¹

The researchers noted that the increased risk of ILI and workdays lost was most pronounced in the timeframe immediately following a COVID-19 booster—such as within the first few weeks—before gradually diminishing.

COVID Shot Boosters Offer No Measurable Short-Term Protection

The study authors concluded that, in the generally healthy, working-age cohort, COVID booster shots offered no measurable short-term protection against illness and might even elevate the risk of becoming symptomatic in the weeks following vaccination. These findings align with other post-pandemic research suggesting not only an increased risk of reinfection shortly after COVID booster doses, but also that, in some studies, receiving more booster doses has not correlated with a reduced risk of infection.^{1 2 3}

While the Swiss study did not directly investigate underlying biological mechanisms, the authors cited hypotheses from previous research, including immune imprinting, altered innate immune responses, and T-cell exhaustion—a condition in which T-cells, a type of white blood cell, after prolonged or repeated exposure to a pathogen or vaccine antigen, lose their ability to function effectively, reducing immune control over the target—following repeated mRNA vaccination. These effects have been documented in both human and animal studies. As one 2023 study observed, “Novel vaccines based on mRNA technology have been recently developed against COVID-19, but much remains to be learned about their wide immunological effects.”^{4 5}

Booster Requirements Remain for Healthcare Workers Despite Mounting Scientific Doubts

Universal COVID booster shot policies have been based on the premise that repeat vaccination can reduce illness and absenteeism among healthcare workers, essentially protecting patients and supporting staffing levels. In this study’s post-pandemic, real-world setting, however, no measurable reduction in these outcomes was observed. The findings instead indicated a potential increase in short-term illness risk. These results suggest a need for further evaluation of whether uniform COVID booster recommendations remain appropriate for all healthcare workers.¹

Many health care systems to this day continue to enforce COVID booster shot mandates that may result in penalties, suspension, or termination for noncompliance. In many cases, religious or philosophical exemptions are denied. In light of emerging data on vaccine effectiveness in different populations, the justification for universal booster requirements appears increasingly difficult to support with current evidence. A meta-analysis published in Vaccines in September 2024 reported that nearly 17 percent of COVID vaccinations in healthcare workers were followed by at least one day of work absence due to side effects, a rate higher than that typically reported after seasonal influenza vaccination. ⁶

New Evidence Call Into Question One-Size-Fits-All Vaccine Policies

Emerging evidence suggests that vaccination policies in healthcare settings should consider not only their effectiveness in preventing infection but also the operational impact of post-vaccination absenteeism in light of existing strains on the healthcare system related to medical workers shortages. The American Medical Association (AMA) has warned of a significant physician shortage in the coming years.⁷

The AMA notes, “There are tremendous gaps in health care today that require the attention of physicians and leaders in organized medicine. Alarming projections about the physician workforce shortage to come ignore the fact that, for many patients in every corner of this country, that shortage has already arrived.”⁷

The Swiss study’s authors conclude, “Based on our data, we conclude that SARS-CoV-2 booster vaccination does not contribute to the protection of the healthcare workforce in a post-pandemic setting. SARS-CoV-2 vaccination may even temporarily increase the likelihood of symptomatic infection and workday loss.” ¹The study findings reflect a growing trend of declining COVID-19 booster uptake among healthcare workers: During the 2023–2024 season, only 15.3 percent of roughly 8 million healthcare personnel across 4,112 U.S. acute care hospitals received a COVID booster.^{1 8}

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