Association between smallpox vaccination and hepatitis C antibody positive serology in Pakistani volunteers.

Goals: To determine whether the smallpox vaccination program has significantly contributed to the widespread prevalence of hepatitis C infection in Pakistan.

Background: Hepatitis C virus has become a worldwide pandemic and has especially devastated developing nations such as Pakistan. There continues to be an increase in fatalities due to hepatitis C-related cirrhosis in Pakistan.

Study: We studied 523 volunteers in the city of Lahore to determine whether the smallpox vaccination program, which ran from 1964 to 1982 in Pakistan, may be responsible for the national surge in hepatitis C viral infection, perhaps because of repetitive use of vaccination devices without proper sterilization or to contaminated vaccine contents.

Results: There was a significantly higher likelihood of hepatitis C antibody seroprevalence in individuals vaccinated for smallpox versus nonvaccinated individuals (21.0% vs. 4.6%, P < 0.001, age-adjusted odds ratio, 3.39; 95% confidence interval, 1.36-8.46). Subjects with positive hepatitis C serology were also more likely to have a history of transfusions (19.2% vs. 9.0%, P = 0.01), but anti-HCV positive serology was not significantly associated with a history of surgery or dental procedures. Following adjustment for age, sex, and history of other conditions, including transfusion, the association between prior smallpox vaccination and hepatitis C antibody seroprevalence remained strong and highly significant (multivariate adjusted odds ratio, 6.11; 95% confidence interval, 2.58-14.51).

Conclusion: These results suggest that the widespread prevalence of hepatitis C infection in Pakistan may be an unintended consequence of the country's smallpox vaccination program and that blood transfusion is also a significant risk factor.