Sir—The paper ‘Assessment of the Direct Effectiveness of BC Meningococcal Vaccine in Rio de Janeiro, Brazil: A Case-Control Study

Only oral cavity and pharynx cancers in Vietnam veterans were significantly elevated, although the doubling of risk on nasal/nasopharyngeal cancer in Vietnam veterans is of interest in light of findings in other studies. The continuing excess of soft tissue sarcoma, non-Hodgkin’s lymphoma and Hodgkin’s Disease is consistent with findings in other studies of people exposed to herbicides. The time period 1988–1993 represents a latency of approximately 18–28 years from the time of maximum use of Agent Orange in Vietnam. This is comparable to the latency range for most solid tumours, and may capture the time period of most interest for tumours induced by exposures in Vietnam. Nevertheless, additional years of follow-up may still be desirable in order to cover the long latency period of some tumours. Also, pooling of data on rare tumours such as nasal/ nasopharyngeal cancer and liver and biliary tract cancer is indicated in order to improve the power and precision of risk estimates.