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A mass vaccination campaign against meningitis in Quebec in the early 1990s proved useless in protecting infants who were the most at risk of contracting the disease, a study published today in a major U.S. medical journal reveals.
And the vaccine that was given probably would no longer be effective in immunizing the rest of the public should another meningitis outbreak strike the province, the lead researcher said yesterday.
Although an experimental vaccine currently in use in England has been shown to be highly effective, it's rarely used in the rest of Europe and not available in Quebec, said Dr. Philippe De Wals, an epidemiologist at the Universite de Sherbrooke.
Still, De Wals said Quebec is probably better prepared to deal with another epidemic of the potentially fatal meningococcal disease, in part because of the findings of his study.
Quebec public-health authorities, for example, now know it would not make sense to use the old vaccine again if an outbreak occurs.
"We found that the vaccine was effective in the first two years after it was administered, but we have no evidence that it worked later on," De Wals said in an interview.
"In other words, it was a short-term vaccine."
At the time that it was introduced, authorities thought the vaccine would be effective for five years.
The Quebec government commissioned De Wals to evaluate the long-term impact of the polysaccharide vaccine after its mass immunization campaign of 1992-93.
The results of the study are published in today's Journal of the American Medical Association.
The researchers discovered that the vaccine was virtually useless in immunizing children between 6 months and 2 years old.
In fact, eight infants who were vaccinated later developed meningococcal disease - a bacterial infection that causes inflammation of the tissue in the brain and spine.
That raises the alarming scenario that the vaccine itself might have been responsible for infecting the infants.
But De Wals refused to jump to that conclusion: "We can't say whether the vaccine caused the illness in these children."
The vaccine was judged 40-per-cent effective in children between the ages of 2 and 9; 75-per-cent effective among those in the 10-to-14 range; and 85-per-cent effective among those 15 or older.
"It's a vaccine that's excellent for adults and the military, but much less effective among the youth," De Wals said.
Although the incidence of meningococcal disease is low, about one case per 100,000 population, news reports of outbreaks strike fear in the hearts of parents. It's a terrifying disease that can strike quickly and kill within hours if untreated.
The provincial government spent up to $30 million immunizing 1.6 million Quebecers, following clusters of the meningococcal disease reported in all age groups across the province in 1991-92.
It was the largest immunization effort since the polio-vaccination campaign of the 1950s.
The researchers noted that the number of cases of the highly contagious disease dropped markedly in 1993 after the mass immunization, and remained low thereafter.
For the period covered under the study, Jan. 1, 1990, until Dec. 31, 1998, a total of 899 cases were reported.
The study compared the numbers of patients who developed meningitis despite being vaccinated with the statistics on those who also fell ill but had not been vaccinated.
De Wal's study was the first to examine the impact of a mass immunization against meningococcal disease.
More than 110,000 infants up to 2 years old were vaccinated, costing the government $1.7 million.
"In retrospect, we can see that it was probably unfounded to use this vaccine on infants," De Wals said. "At the time, there was a lot of uncertainty and a political decision was made."
Preliminary results indicate that the experimental conjugate vaccine in use in England since November 1999 is 80- percent effective for all age groups combined. By comparison, the polysaccharide vaccine is considered to have an over-all success rate of 60 per cent.
"If we were to carry out another mass vaccination across Canada, it would make more sense to use the new vaccine, certainly for the most young," he said. "But the problem is that there's a shortage of the vaccine in England. It also costs 10 times more than old vaccine.
"I think that as a result of our study, the government and pharmaceutical companies should accelerate the process of producing the new vaccine," De Wals added.
Meningococcal disease is transmitted though contact with secretions from the nose and throat of an infected person. Symptoms include high fever, severe headaches, neck stiffness, nausea and vomiting.
There are two common types: meningococcal meningitis and meningococcal septicemia. Septicemia is the type that most often kills.
Across Canada each year, there are about 250 to 300 cases of meningococcal disease, usually during the winter months. Most are isolated cases.
