The effectiveness of chickenpox vaccine decreases with time

On Wednesday, US researchers reported that the Varivax vaccine against chickenpox produced by Merck not only lost its effect after a while but also changed its expression style. of this disease in people.

This study helps confirm what doctors already know that the protective effect of the vaccine does not last long.

They said that according to information from actual cases, those who had not been vaccinated or those who had the first dose of vaccine did not work, were later affected by this highly contagious disease, when he is at greater risk of serious complications.

A child with chickenpox(Photo: wikipedia)

Jane Seward of the Centers for Disease Control and Prevention (CDC) in Atlanta, who conducted the study, said: 'If you have not been vaccinated, and later you have it, the risk of death will 20 times higher than when they were sick at a young age, and the opportunity to hospitalize is 10-15 times higher. '

For the first time, the results of this study were fully published in the New England Journal of Medicine on Thursday, and created an impact. This result forces the CDC Immunization Advisory Committee to recommend that children aged 4-6 need booster doses. The committee also said that in June 2006, children, adolescents and adults should also receive booster doses.

The team - led by Ms Sandra Chaves of the CDC - said no one knew how long the second injection had a protective effect.

The United States has been vaccinating chickenpox since 1995, but tests show that the vaccine does not have a good protective effect in only 10-15% of children receiving the single dose. The second injection dose will definitely increase the protective effect, but it is unclear to what extent.

Ms. Seward, acting deputy director of the CDC's department of viral illness, said: 'Instead of being valid for 80-85%, we hope that the second dose will be effective 90-95%.'

Chavez's group used data on vaccination and disease collected from Antelope Valley, California to monitor the effect of Varivax vaccine.

Between 1995 and 2004, the vaccine reduced the number of chickenpox cases by about 85%. In 1995, only 1% of 2,794 cases were reported to be in children who were vaccinated. In 2004, there were fewer cases of chickenpox, 420 cases, but up to 60% fell into immunized children.

Although 73% of children with chickenpox in 1995 were under 7 years of age, this rate fell to 30% in 2004 because they tend to get chickenpox as they get older. In the case of vaccinated children who become ill, the disease tends to be worse, probably because they are older than before.

The researchers write the following: 'The risk of getting vaccinated at least 5 years ago by children aged 8-12 years can be as high as twice as high as that of children who are vaccinated. prevented less than 5 years ago. '

In May last year, Zostavax, another vaccine prepared by Merck, was used to give booster shots to licensed adults.

The virus that causes chickenpox still exists in our bodies for a lifetime and can reactivate like shingles, a form of rash that can be painful for years. Chickenpox is often considered a harmless disease in children, but before the vaccine prevents the disease, every year in the United States alone there are up to 100 deaths due to complications of this disease.

Hong Linh