Chickenpox
Vaccine

Chickenpox can be prevented by vaccination. The side effects are usually mild, such as some pain or swelling at the injection site.

A live attenuated varicella vaccine, the Oka strain, was developed by Michiaki Takahashi and his colleagues in Japan in the early 1970s. In 1995, Merck & Co. licensed the "Oka" strain of the varicella virus in the United States, and Maurice Hilleman 's team at Merck invented a varicella vaccine in the same year.

The varicella vaccine is recommended in many countries. Some countries require the varicella vaccination or an exemption before entering elementary school. A second dose is recommended five years after the initial immunization. A vaccinated person is likely to have a milder case of chickenpox if they become infected. Immunization within three days following household contact reduces infection rates and severity in children. Being exposed to chickenpox as an adult (for example, through contact with infected children) may boost immunity to shingles. Therefore, it was thought that when the majority of children were vaccinated against chickenpox, adults might lose this natural boosting, so immunity would drop and more shingles cases would occur. On the other hand, current observations suggest that exposure to children with varicella is not a critical factor in the maintenance of immunity. Multiple subclinical reactivations of varicella zoster virus may occur spontaneously and, despite not causing clinical disease, may still provide an endogenous boost to immunity against zoster.

The vaccine is part of the routine immunization schedule in the US. Some European countries include it as part of universal vaccinations in children, but not all countries provide the vaccine. In the UK as of 2014, the vaccine is only recommended in people who are particularly vulnerable to chickenpox. This is to keep the virus in circulation, thereby exposing the population to the virus at an early age, when it is less harmful, and to reduce the occurrence of shingles through repeated exposure to the virus later in life. In November 2023, the UK Joint Committee on Vaccination and Immunisation recommended all children be given the vaccine at ages 12 months and 18 months; however, this has not yet been implemented. In populations that have not been immunized or if immunity is questionable, a clinician may order an enzyme immunoassay. An immunoassay measures the levels of antibodies against the virus that give immunity to a person. If the levels of antibodies are low (low titer) or questionable, reimmunization may be done.
length_constraints:number_words[403], startend:quotation, detectable_format:multiple_sections[5]