Does Influenza Vaccine During Pregnancy Prevent Influenza-Related Hospitalizations?

One study found that the vaccine offers "moderate" protection. Only about half of pregnant women were vaccinated against influenza last year.

This article was published for the first time on 14 October 2018 on Medpage Today.

By Molly Walker

The researchers found that the influenza vaccine offered moderate protection to pregnant women against influenza-related hospitalizations.

The adjusted efficacy of influenza vaccine was 40% (95% CI, 12% to 59%) against influenza-related hospitalization during pregnancy, said Mark G. Thompson, PhD , CDC and colleagues.

In addition, between 2010 and 2016, 13% of pregnant women who tested positive for influenza were vaccinated, compared to 22% of pregnant women who tested negative, according to the study of Clinical Infectious Diseases.

Recent data from the CDC suggest that only about half of pregnant women were vaccinated against influenza last year, but the authors cited the "lack of data" on the effectiveness of influenza vaccine in preventing the serious consequences of influenza, since randomized trials would be "contrary to the ethic".

Researchers examined data on pregnant women aged 18 to 50 and live births or stillbirths with gestations ≥ 20 weeks of age, whose pregnancies overlapped with influenza seasons from 2010 to 2016 .

The team analyzed the PREVENT (Pregnancy Vaccine Efficacy Network) network, which contained laboratory data, medical records and immunization records in Australia, Canada, Israel and the United States. -United. The authors estimated the effectiveness of the influenza vaccine to confounders.

A discharge diagnosis of "acute respiratory or febrile illness" was identified using ICD-9 and ICD-10, and the authors noted that hospitalizations for acute respiratory or febrile illness were not included only if a clinician prescribed a real-time reverse transcription polymerase chain reaction (rRT-PCR) for screening for influenza in the 3 days prior to admission until the date of exit.

Overall, just under 19,500 hospitalizations were diagnosed at the exit of the "Acute or Febrile Respiratory Disease" program, and only 6% of them were screened for rRT-PCR flu.

Thompson and their co-authors noted that most hospitalizations for acute respiratory or febrile illness involved women under 35, two-thirds in the third trimester, and two-thirds with no high-risk medical conditions. The authors wrote that the main diagnosis at discharge was about an acute respiratory or febrile illness for about half of all hospitalizations.

Of these hospitalizations, approximately 60% were infected with the influenza virus. The authors found that, compared with pregnant women with hospitalized hospitalizations for acute respiratory or febrile illness, pregnant women with influenza were more likely to be in the third trimester and less likely to have a high-risk disease.

The researchers also found a 55% influenza vaccine efficacy rate in women hospitalized during the first or second trimester. This could contribute to discussions about the benefits of early maternal immunization, especially during the first trimester, the researchers noted.

The authors also stated that the findings could be relevant to "several public health policy and research debates", including the lack of evidence of the effectiveness of influenza vaccine against confirmed influenza confirmed in the laboratory during the pregnancy, which has been "described as an obstacle to expanding maternal flu vaccination programs" in low- and middle-income countries.

The study was funded in part by the CDC. Thompson did not reveal any conflict of interest. Other co-authors have announced support from Johnson & Johnson (Jannsen Pharmaceuticals), Pfizer, MedImmune / AstraZeneca, Merck, GlaxoSmithKline, Sanofi Pasteur, Protein Science, Novartis (now GSK) and Dynavax.