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People with chronic inflammatory disease (CID) had a distinct adverse event profile following COVID-19 vaccination.

That's according to a study in in which 441 participants (322 CID patients, 119 controls) were included. All participants had completed three study visits: one before the vaccine, another after the first dose, and again after the second dose. Adverse events -- injection site pain, injection site redness, headache, fever, rash, myalgia, arthralgia, fatigue, nausea, and diarrhea -- were assessed within 7 days of receiving each dose.

Patients with CID reported greater symptom severity than control patients after dose 1 (P=0.0001), including more myalgia and fatigue (P<0.05). For immunogenicity, higher symptom severity after dose 1 and a higher number of symptoms after dose 2 were associated with higher antibody titers (P<0.05). Site pain was the most common adverse event after dose 1 (105%, P=0.03); fatigue was most common after dose 2 (113%, P=0.004).

Monica Yang, MD, rheumatology fellow at the University of California San Francisco and first author, discussed the study with the Reading Room. The exchange has been edited for length and clarity.

What was the central question this study was designed to address?

Yang: The goal was to characterize the reactogenicity (adverse event profile) of patients with CID to the COVID-19 vaccines and to understand the relationship between reactogenicity and immunogenicity (antibody response) in this patient population.

Why is it particularly important to understand COVID-19 reactogenicity in the CID population?

Yang: Given that people with CID have a dysregulated immune system and require immunosuppressive medications, they may face increased risk of developing severe illness from COVID-19 infection. As such, immunization is critical in this population.

At the same time, concerns regarding adverse effects and the novelty of the mRNA vaccines can contribute to vaccine hesitancy. Therefore, elucidating the reactogenicity profile of patients with CID will better inform patients and providers. Further, understanding the link between reactogenicity and immunogenicity in this patient population is important given that vaccine immune response may be blunted.

How would you summarize your key findings?

Yang: We found that people with CID had more severe symptoms, with more fatigue and muscle aches, following the first dose of COVID-19 vaccine than healthy controls. However, after the second dose, those with CID had side effects similar to those of healthy controls.

Women and patients younger than 65 also tended to have more severe side effects. With regard to antibody response, we found that higher symptom severity after dose 1 and more numerous symptoms after dose 2 were both associated with higher antibody titer. In fact, each increase of one symptom following vaccination was associated with a 15.1% increase in antibody response.

What are the take-home messages for clinicians?

Yang: Overall, we found that patients with CID had a distinct reactogenicity profile following the first dose of the vaccine.

It has been hypothesized that increased symptomatology following vaccination may indicate increased immune response. However, this has yet to be demonstrated in vaccine studies. In our study we demonstrated a link between reactogenicity and immunogenicity, with increased adverse events and certain specific adverse events associated with increased antibody titers. This finding, present among CID patients and controls, mechanistically supports the underlying physiology of vaccination with immunity coming about via stimulation of the immune system.

While it is still unclear what clinical significance these differences in antibody titers may have, reactogenicity may be a signal for robustness of immune response in certain populations.

We also found the presence of more numerous symptoms and select adverse events following vaccine was associated with increased antibody titers.

Overall, this study serves to provide much-needed safety data for patients with CID and as an initial step to better understanding the link between reactogenicity and immunogenicity following COVID-19 vaccines.

Implications for practice

• People with CID have a distinct reactogenicity profile to COVID-19 vaccination.
• Higher symptom severity after dose 1 and a higher number of symptoms after dose 2 were associated with higher antibody titers.
• Reassuring safety data may help alleviate vaccine hesitancy.

Read the study here and expert commentary on the clinical implications here.