Tuesday, August 16, 2016

When Flu Vaccine Studies Collide

Credit CDC


Regular readers of this blog are well aware that science is a process, and sometimes, it can be messy and inconsistent. On several occasions (see When Studies Collide (Revisited)),  we've looked at studies that have come to widely differing conclusions on some pretty important topics.

Whether its the gauging the effectiveness of oseltamivir in treating influenza, the relative protectiveness of surgical masks vs N95 respirators in preventing respiratory infections, or the value of statins in treating or preventing pneumonia, consensus can sometimes be elusive. 

Case in point, earlier this summer ACIP (Advisory Committee for Immunization Practices) - which had previously expressed a preference for the nasal mist vaccine over the shot for children (see CIDRAP ACIP cites preference for nasal-spray flu vaccine for young) reversed themselves after reviewing two years of disappointing data, and recommended against its use. 

Last June, in CDC Statement On ACIP Recommendation Against Use Of Inhaled (LAIV) Flu Vaccine, we looked at LAIV's unexpected fall from grace, and the CDC's  response. 

Less than a week later, in UK PHE Stands By The Nasal Spray Flu Vaccine, we saw a contrarian opinion voiced by  Public Health England, which cited their own studies backing up the effectiveness of the nasal mist vaccines.

Today the Annals of Internal Medicine has published a new study which finds  - at least among the Hutterite cohort studied - that the LAIV nasal mist vaccine provided similar protection to that observed from the Inactivated Influenza Vaccine (IIV) flu shot.

Live Attenuated Versus Inactivated Influenza Vaccine in Hutterite Children: A Cluster Randomized Blinded Trial

Mark Loeb, MD; Margaret L. Russell, MD, PhD; Vanessa Manning, BSc; Kevin Fonseca, PhD; David J.D. Earn, PhD; Gregory Horsman, MD; Khami Chokani, MD; Mark Vooght, MD; Lorne Babiuk, PhD; Lisa Schwartz, PhD; Binod Neupane, PhD; Pardeep Singh, BSc; Stephen D. Walter, PhD; and Eleanor Pullenayegum, PhD

Ann Intern Med. Published online 16 August 2016 doi:10.7326/M16-0513
© 2016 American College of Physicians

Background: Whether vaccinating children with intranasal live attenuated influenza vaccine (LAIV) is more effective than inactivated influenza vaccine (IIV) in providing both direct protection in vaccinated persons and herd protection in unvaccinated persons is uncertain. Hutterite colonies, where members live in close-knit, small rural communities in which influenza virus infection regularly occurs, offer an opportunity to address this question.


Results: Mean vaccine coverage among children in the LAIV group was 76.9% versus 72.3% in the IIV group. Influenza virus infection occurred at a rate of 5.3% (295 of 5560 person-years) in the LAIV group versus 5.2% (304 of 5810 person-years) in the IIV group. The hazard ratio comparing LAIV with IIV for influenza A or B virus was 1.03 (95% CI, 0.85 to 1.24).

Limitation: The study was conducted in Hutterite communities, which may limit generalizability.

Conclusion: Immunizing children with LAIV does not provide better community protection against influenza than IIV.

Primary Funding Source: The Canadian Institutes for Health Research.

This appears to be a well mounted study, although like all studies, it suffers from some limitations.  But of all of the studies I've seen on the effectiveness of the LAIV, I can say without reservation or fear of contradiction  . . . this is the most recent.

Beyond that, I'm afraid we're going to have to wait for more data to come in.  The tie-breaker doesn't necessarily go to the last paper to be published.

We'll likely get that data from this upcoming flu season, where we'll have the U.S. vaccine effectiveness rates to compare with those countries continuing to use the LAIV. 

The CDC will no doubt be reviewing all of this for next year's vaccine program.  Perhaps, by then we'll know which way the mist is blowing.

Stay tuned.

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