Effectiveness of inactivated influenza vaccines wanes during the course of a single influenza season; therefore, clinicians may want to reconsider the optimal timing of seasonal influenza vaccination. Researchers identified US individuals who were vaccinated with inactivated influenza vaccine from September 1, 2010 to March 31, 2017, and who were subsequently tested for influenza and respiratory syncytial virus (RSV). Test-confirmed influenza was the primary outcome and days-since-vaccination was the predictor of interest in conditional logistic regression. Among the findings:
- Individuals vaccinated 42 to 69 days prior to being tested had 1.32 times the odds of testing positive for any influenza compared to those vaccinated 14 to 41 days prior to being tested.
- The odds ratio (OR) increased in linear fashion by ~16% for each additional 28 days since vaccination.
- The OR was 2.06 for individuals vaccinated ≥154 days prior to being tested.
- No evidence of waning was found for RSV.
Ray GT, Lewis N, Klein NP, et al. Intra-season waning of influenza vaccine effectiveness. [Published online ahead of print September 10, 2018]. Open Forum Infect Dis. doi:10.1093/cid/ciy770.
This potentially could be a very important study. The arrival of flu vaccine seems to happen earlier and earlier each year, with distribution and administration against influenza starting in the summer. A CDC study looking at 25 years of influenza activity found that February is the most common month for influenza infections in the United States. If we use the 150-day mark as the cutoff for good efficacy and hope to have protection through mid-March, we should vaccinate our patients from mid-October on. The ACIP recommends that we give influenza vaccine as soon as we get the vaccine. This study would argue that we should revert to the older model to vaccinate patients beginning in mid-October. —John Russell, MD