From Michael Sauri, Occupational Medicine Clinic, Rockville
Your report on whether people vaccinated against smallpox decades ago still have immunity correctly states that only about 40 of 621 people still had protection. That’s 6.4 per cent of the total (1 June, p 7). But a more detailed analysis suggests that 9.4 per cent might be more accurate, as not all of the 621 had definitely had previous vaccinations.
Rockville, Maryland
