Vaccinating children against chicken pox has an added benefit in protecting infants who come into contact with vaccinated kids, researchers from the CDC (Centers for Disease Control and Prevention) reported in the journal Pediatrics. Infants – babies less than twelve months old – are not eligible for the chicken pox vaccine. The authors added that improving varicella (chicken pox) vaccination coverage in people of all ages will reduce varicella exposure even more, resulting in better protection for those not eligible for the vaccination.

Infants used to be four times as likely to die from varicella before 1995 than they are today. In 1995, the varicella vaccine was made available to children aged at least 12 months. Also, the incidence of chicken pox today among infants is 89.7% lower than it was in 1995 – a drop from 15.6 cases per 1,000 infants to 1.6 per 1,000.

Infants who get chicken pox have a risk of developing complications, such as pneumonia or a secondary skin infection. Last year in the USA over 100 children died from chicken pox.

The authors reported that the distribution of chicken pox according to age also changed considerably after the introduction of the vaccine. In 1995, the disease was much more common among children aged 1 to 10 years, followed by infants, and then those aged from 10 to 14 years. In 2008, the rate become more evenly spread across all age groups.

Team leader, Sandra Chavez M.D., and colleagues wrote:

“After implementation of the varicella vaccination program in the United States in 1995, a remarkable decline in varicella morbidity and mortality was documented. A community-based varicella active surveillance project in the United States provided investigators with the opportunity to examine 14 years of data (1995-2008) that could be used to better describe the epidemiology and clinical presentation of varicella disease in infants.”

In 1995, active surveillance projects were established in West Philapdelpha and Antelope Valley, Los Angeles County. Over 300 reporting centers provided fortnightly data on identified chicken pox cases. The sick child’s parent or guardian was interviewed in each case, in order to gather epidemiologic, clinical and geographical data.

The researchers found that as the 1997 to 2008 period progressed, very young infants (five months old or less) were getting milder disease compared to the older infants.

The researchers found that:

  • 58% of sick infants in 1995 had at least 50 lesions, compared to 49% in 2008
  • 21% of infants had fevers in 1995, compared to 12% in 2008
  • 15% of infants had disease-related complications in 1995, compared to 6% in 2008
  • 14% of infants were prescribed antibiotics in 1995, compared to 6% in 2008

The researchers concluded that the Varicella vaccination program brought about considerable indirect benefits for infants.

They wrote (conclusion):

“Presence of maternal varicella-zoster virus antibodies might explain attenuated disease in very young infants likely born to mothers with history of varicella. Although varicella disease incidence has declined, exposure to varicella-zoster virus continues to occur.

Improving varicella vaccination coverage in all age groups will further reduce the risk of varicella exposure and protect those not eligible for varicella vaccination.”

The varicella vaccine (chicken pox vaccine) is an attenuated (live but weakened) virus that protects the patients from VZB (Varicella Zoster Virus). In the USA the vaccine is called Varivax and is manufactured and marketed by Merck. Zostavax, another vaccine which is a larger-than-normal dose of Varivax, is used to reduce the risk of shingles.

In the USA, 41 states require that a child be vaccinated before attending a state-run elementary school. All US states offer a medical exemption, while 48 states offer philosophical and/or religious exemptions.

Written by Christian Nordqvist