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Pandemic H1N1 vaccines were effective

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CHICAGO — Adjuvant H1N1 influenza vaccines were effective during the 2009 pandemic but there are several questions still unanswered, according to a presentation here.

“What remains are several questions, several controversies and room for uncertainty that is inherent for observational research in comparison to a randomized trial,” said Jacek Z. Mrukowicz, MD, PhD, Director of the Polish Institute for Evidence-Based Medicine, Krakow, Poland.

Mrukowicz reviewed what he considered to be the most important papers published in the past year related to vaccines, and he chose two papers about pandemic influenza vaccine. Poland was the only European Union country that refused to buy the pandemic vaccines. It was the decision of the minister of health, according to Mrukowicz.

He discussed the H1N1 vaccine observational case-control study by Skowronsk and colleagues that reported that the monovalent AS03 adjuvanted vaccine used in Canada during the 2009 pandemic was highly effective in prevention of medically-attended, laboratory-confirmed pandemic H1N1 illness, with specific reference to a single dose in children and young adults.

“Across the sensitivity analysis, the effectiveness is very similar except for the patients vaccinated less than 2 weeks before onset of ILI. The effectiveness is 55.2% for this reason,” Mrukowicz said.

“This type of clinical trial design, which is a specific type of case control study, controls inherently for a type of selection bias, which is a different type of health care-seeking behavior that may influence vaccination status,” he said.

Pandemic H1N1 was detected by reverse transcription polymerase chain reaction in 209 of 552 (38%) participants from 500 community-based clinics during the primary analysis period. Rates were highest in children and young adults (40%) and lowest in people aged 65 years old and older (9%).

The researchers reported 93% adjusted vaccine effectiveness overall (95% CI 69% to 98%).

Mrukowicz also reviewed Influenza Monitoring Vaccine Effectiveness in Europe (I-MOVE), a multicentre case-control study, which was of similar design as the Canadian study. The study concluded that the pandemic monovalent vaccine provided good protection against medically-attended pH1N1 and no effect of the 2009-2010 seasonal influenza vaccine.

The study investigators wrote, however, that the late availability of the pandemic vaccine and subsequent limited coverage with this vaccine hampered their ability to study vaccine benefits during the outbreak period.

For more information:

• Mrukowicz J. #62. Hot Topics in Vaccines. Presented at: 51st ICAAC. Sept. 17-20, 2011. Chicago.
• Skowronski, DM. BMJ 2011;342:c7297:doi:10.1136/bmj.c7297.
• Valenciano M. PLoS Med. 2011 Jan;8(1):e1000388. Epub 2011 Jan 11.

Disclosure: Dr. Mrukowicz reports no relevant financial disclosures.

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