The first-ever known cases of meningitis due to chickenpox vaccine reactivation have been reported in two 14-year-old boys who received both the recommended dosages.

While one of the boys was reported to be immunocompromised, the other one was a previously-healthy boy. The former had a history of leukemia and experienced symptoms like numbness and slurred speech. They were both treated with the antiviral drug acyclovir.

The varicella vaccine that is licensed for use in the United States nearly twenty-five years ago has been considered extremely safe, even though it is not recommended for pregnant women and individuals with compromised immune systems. In certain rare cases, the live, reduced virus used in the vaccine can cause reactivation of herpes zoster or shingles, just like what happened to individuals infected with chickenpox.

"Varicella vaccine is an incredibly safe and effective vaccine that has dramatically reduced the incidence of chickenpox in the US. Over 50 million doses have been distributed, and this rare side effect has only been described in a handful of cases," the study’s lead author Dr. Whitney Harrington told CNN Health via an email, "In contrast, meningitis is a well-known complication of chickenpox and pose a far greater risk to children."

Previous cases of reactivated vaccine Oka (vOka) resulting in meningitis have been described in young kids who had received only a single dose of the vaccine. There has been very little information about the vOka reactivation in older kids after the 2-dose series of vaccination.

Also, previous research has shown that herpes zoster occurred more commonly among the unvaccinated kids than the ones who were vaccinated. Also, among the vaccinated children, the herpes zoster has been reported to have acquired from the virus via an infected person and not through vaccination.

The Centers for Disease Control and Prevention (CDC) recommends that all children receive both the doses of the vaccine routinely: the first one between 12 months and 15 months of age and the next one when the child is aged between 4-6 years. The CDC also reported that the varicella vaccine helps prevent more than 3.5 million cases of chickenpox, 100 deaths and 9000 hospitalizations in the U.S. every year.

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