Vaccination rates drive measles case trends

Steps:

• Review vaccination percentages: stable or high around 90% in 2004, possibly declining later.
• Analyze measles cases: decreasing from 1999 to 2004, then rising from 2005 to 2008.
• Correlate high 2004 vaccination with pre-2004 case drop.
• Test each statement against these trends for matches.

Why B is correct:

• 90% vaccination exceeds herd immunity threshold (typically 90-95% for measles), directly causing case reduction per epidemiological principles.

Why the others are wrong:

• A: Vaccination rates remained high or stable, not decreasing yearly.
• C: Vaccine efficacy holds; post-2005 case rise likely from slight vaccination dips or outbreaks, not inefficacy.
• D: Vaccination rates did not decrease overall; case increase ties to later factors.

Final answer: B