A first dose of COVID-19 vaccine accelerated relief of long-COVID symptoms such as fatigue and muscle aches in UK adults, but flu vaccination did not, suggests an observational University College London–led study published yesterday in the Journal of Infection.
The researchers used data from the ZOE COVID Symptom Study app to compare improvement in long-COVID symptoms in the second week before and after COVID-19 vaccination in patients receiving their first dose with that in matched unvaccinated patients (1,679 in each group; 69.4% women) starting in November 2020. They also performed the same analysis in long-COVID patients receiving a flu vaccine dose and their unvaccinated peers (692 in each group).
Given UK SARS-CoV-2 variant prevalence during the flu vaccination campaign, patients were likely to have been infected by the Delta variant, but this was not formally tested, the authors noted.
“Some individuals experience otherwise unexplained persistent symptoms after COVID-19, now categorized as ongoing symptomatic COVID-19 [OSC] (symptoms for 4 – 12 weeks) or the post COVID-19 syndrome [PCS] (symptoms for more than 12 weeks),” they wrote. “Both OSC and PCS can disrupt activities of daily living, with dyspnoea [shortness of breath], severe fatigue, anosmia [loss of smell] and headaches amongst the commonest reported symptoms.”
Lower odds of 13 symptoms after COVID vaccine
After COVID-19 vaccine receipt, the likelihood of experiencing 13 symptoms in long-COVID patients was lower than that of unvaccinated participants. These symptoms included fatigue, loss of smell, cough, shortness of breath, nasal discharge, muscle pain, brain fog, low mood, chest pain, tinnitus, delirium, and rash.
Symptom worsening was less common in vaccinated than unvaccinated participants (23 of 29 symptoms), except for loss of appetite, brain fog, sneezing, tinnitus (ringing in the ears), earache, and heart palpitations.
Symptom burden improved significantly more in COVID-vaccinated patients after vaccination than in unvaccinated patients for eight symptoms, including fatigue, shortness of breath, muscle pain, low mood, chest pain, diarrhea, tinnitus, and a burning sensation on the skin.
After flu vaccine receipt, of the 12 symptoms common to both analyses (before and after vaccination), absence of change/limited change was most often reported for fatigue (58.3% prospective vs 50.4% retrospective), chest pain (53.2% vs 59.3%, respectively), hoarse voice (58.3% vs 59.4%), and sore throat (51.8% vs 41.4%).
Potential mechanisms unclear
Symptoms that improved the most in both prospective and retrospective symptom reporting were cough (71.3% prospective vs 51.6% retrospective), loss of appetite (77.5% vs 45.2%, respectively), and diarrhea (58.7% vs 37.0%).
We recognize that all observational designs are subject to biases (such as selection bias); and a priori individual expectations around SARS-CoV-2 vaccination and influenza vaccination were unlikely to be the same.
In the prospective analysis, more participants reported symptom improvement than worsening for all symptoms. Likewise, in the retrospective analysis, more patients reported improvement of all symptoms except muscle pain, abdominal pain, and fever, but overall, the percentage in the “worsened” category was much higher in the retrospective analysis than in the prospective study.
“The data suggest that [COVID] vaccination may contribute to symptom recovery of OSC/PCS, though potential mechanisms remain to be explored,” the researchers wrote.
“In contrast, vaccination against influenza was not associated with reduction in key COVID-19 symptoms,” they added. “However, we recognize that all observational designs are subject to biases (such as selection bias); and a priori individual expectations around SARS-CoV-2 vaccination and influenza vaccination were unlikely to be the same.”
Noting that the retrospective assessment generated less-impressive results, the authors said, “This highlights the effect of recall bias in retrospective population symptom reporting. Further, evaluating symptoms retrospectively might also be affected by ‘memory-experience gap’— individuals may only notice an improvement above a certain threshold, which may explain starker impression of condition stability in the retrospective survey.”
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