ATLANTA - In 1963, widespread skepticism met the notion that smallpox would someday be eradicated, yet 16 years later the world's last case of smallpox occurred. According to R. Palmer Beasley, MD, dean, School of Public Health, University of Texas in Houston, worldwide eradication of hepatitis B virus (HBV) will be easier than the eradication of smallpox, polio or measles.
"Although we have to live with the cohort of aging carriers in the process of getting rid of [HBV], they are essentially noninfectious and will not contribute to the pool of new infectees," said Beasley. "It's basically perinatal transmission that is the driving force of infections worldwide.
"I think it's fair to say it was not in any of our minds - no matter how optimistic we were only a few years ago - that we'd be getting carrier rates down to around 1% in various populations. Now we've got Taiwan, which is the leader of the gang, down to less than 1%."
Biology favors eradication, according to Beasley. Surface antigen rates decline with age, and with increasing age, antigen and infectivity are lost more rapidly. Subsequently, risk of transmission is highest from mother to infant.
Incidence studies show the carrier rate, almost 100% at birth, drops to about 50% at 1 year; about 25% at 2 to 4 years; and between 2% to 5%, perhaps less, in adults. "So, it is only really children that matter in the phenomenon of being able to deal with this infection," said Beasley. "The strategy is really simple; it only requires immunization of newborns. But, it can be achieved more slowly if initial immunization is delayed to one or two months of age, as with other routine childhood immunizations."
The hepatitis B vaccine (HepB) given at 1 month compared with the birth dose is still efficacious and beneficial in programs where the birth dose is not possible.
The ideal vaccination program, according to Beasley, would be a birth dose followed by a dose at 3 and 6 months, with catch-up programs when needed. Different countries will need different strategies, he noted.
HepB is highly immunogenic and highly efficacious. "I'd like to put forward the notion that two doses may be sufficient, it hasn't really been tested, but in situations where only a dose or two is given and the third dose is impossible, I think there's good reason to believe that two will be effective," said Beasley. Booster doses, if they hold any value, will only protect adults from adult disease - they have nothing to do with carriage, he said.
Costs of HepB are low and dropping as more vaccine manufacturers are coming on board. If vaccine prices fall, Beasley said it would be sensible to change the dosing strategy and use a higher concentration with two doses.
HepB vaccination can withstand an interruption. Beasley considered this a nightmare for more infectious agents like smallpox, polio and measles, where a break in the vaccination program could be disastrous since those diseases can reestablish themselves.
"[With the vaccine,] we can eliminate 75% to 80% of hepatocellular carcinoma, plus a high proportion of chronic liver disease," he said. "If we don't eliminate HBV, does any cancer vaccine stand a chance?"
For more information:
- Beasley R. Is elimination a realistic goal for vaccine preventable chronic infection? Opening session. Presented at the 10th International Symposium on Viral Hepatitis and Liver Disease. April 9-13, 2000. Atlanta.
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