[13] In the United Kingdom, Varilrix, a live viral vaccine[14] is approved from the age of 12 months, but only recommended for certain at risk groups.

[9] A live attenuated varicella vaccine, the Oka strain, was developed by Michiaki Takahashi and his colleagues in Japan in the early 1970s.

[15] American vaccinologist Maurice Hilleman's team developed a chickenpox vaccine in the United States in 1981, based on the "Oka strain" of the varicella virus.

[22] Follow-up evaluations have taken place in the United States of children immunized that revealed protection for at least 11 years.

Assessments of the duration of immunity are complicated in an environment where natural disease is still common, which typically leads to an overestimation of effectiveness.

Persons exposed to the virus after vaccination tend to experience milder cases of chickenpox if they develop the disease.

[42] The CDC stated in 2014: "Chickenpox vaccines contain weakened live VZV, which may cause latent (dormant) infection.

"[43] The risk of shingles is significantly lower among children who have received varicella vaccination, including those who are immunocompromised.

[42][44] A population with high varicella vaccination also has lower incidence of shingles in unvaccinated children, due to herd immunity.

For a catch-up vaccination, individuals between 7 and 12 years old should receive a two-dose series 3 months apart (a minimum interval of 4 weeks).

[49] As there is an increased risk of shingles in adults due to possible lack of contact with chickenpox-infected children providing a natural boosting to immunity, and the fact that chickenpox is usually a mild illness, the NHS cites concerns about unvaccinated children catching chickenpox as adults when it is more dangerous.

[10] Specific antiviral medication, such as acyclovir, famciclovir, or valacyclovir, are not recommended 24 hours before and 14 days after vaccination.

On some occasions, severe reactions such as meningitis and pneumonia have been reported (mainly in inadvertently vaccinated immunocompromised children) as well as anaphylaxis.

Adverse reaction reports for the period 1995 to 2005 found no deaths attributed to the vaccine despite approximately 55.7 million doses being delivered.

The literature contains several reports of adverse reactions following varicella vaccination, including vaccine-strain zoster in children and adults.

[4][5][6] Takahashi and his colleagues used the Oka strain to develop a live attenuated varicella vaccine in Japan in the early 1970s.

[60] American vaccinologist Maurice Hilleman's team at Merck then used the Oka strain to prepare a chickenpox vaccine in 1981.

[63] Twelve European countries (Austria, Andorra, Cyprus, Czech Republic, Finland, Germany, Greece, Hungary, Italy, Latvia, Luxembourg and Spain) have universal varicella vaccination (UVV) policies, though only six of these countries have made it available at no cost via government funding.

[63] EU member states that have not implemented UVV cite reasons such as "a perceived low disease burden and low public health priority," the cost and cost-effectiveness, the possible risk of herpes zoster when vaccinating older adults, and rare fevers leading to seizures after the first dose of the MMRV vaccine.

[63] "Countries that implemented UVV experienced decreases in varicella incidence, hospitalizations, and complications, showing overall beneficial impact.

"[63] Varicella vaccination is recommended in Canada for all healthy children aged 1 to 12, as well as susceptible adolescents and adults 50 years of age and younger; "may be considered for people with select immunodeficiency disorders;[23] and "should be prioritized" for susceptible individuals, including "non-pregnant women of childbearing age, household contacts of immunocompromised individuals, members of a household expecting a newborn, health care workers, adults who may be exposed occupationally to varicella (for example, people who work with young children), immigrants and refugees from tropical regions, people receiving chronic salicylate therapy (for example, acetylsalicylic acid [ASA])," and others.

[65] Other countries, such as the United Kingdom, have targeted recommendations for the vaccine, e.g., for susceptible healthcare workers at risk of varicella exposure.

Since the cell strains in use originate from abortions, there has been some opposition to the practice and the resulting vaccines on religious and moral grounds.