Controversy surrounding SK bioscience's chickenpox vaccine resolved

The Korea Disease Control and Prevention Agency (KDCA) said that the chickenpox vaccine Sky Varicella, developed by SK bioscience, poses no significant safety risks.

This conclusion follows an extensive investigation and analysis carried out by the KDCA in collaboration with experts and the Ministry of Food and Drug Safety (MFDS).

The investigation was prompted by an increase in reports of adverse reactions following vaccination with Sky Varicella. The KDCA formed a joint public-private working group to evaluate the vaccine's safety and efficacy on April 26 per request from the Immunization Subcommittee.

This included consultations with expert advisory committees and the Immunization Subcommittee, examining both domestic and international data on chickenpox and shingles incidence, and assessing the safety of the vaccine within the national immunization program.

The MFDS reviewed the vaccine's quality, non-clinical, and clinical trial data submitted during the approval process, as well as national lot release test results and adverse event reports.

Their comprehensive evaluation found no significant safety issues associated with the vaccine. Clinical trials conducted in Korea demonstrated that the vaccine's safety and efficacy were comparable to those of the control group (MSD's Varivax).

Since 2018, 1,888,631 doses of chickenpox vaccine have been administered, with 29 reported cases of shingles, resulting in a reporting rate of 0.0015 percent.

Specifically, the Sky Varicella vaccine had a shingles reporting rate of 0.003 percent.

The KDCA's investigation revealed that all 29 individuals who developed shingles after vaccination recovered without serious complications. Big data analysis by the National Health Insurance Service also indicated no significant differences in the severity of shingles cases post-vaccination between different vaccines.

The investigation also looked into a suspected death related to the chickenpox vaccine that was reported in a research paper.

The research paper, published in the Journal of Medical Virology last September, noted that the OKA/SK strain used in Sky Varicella, which is actively prescribed domestically, caused fatal disseminated chickenpox in a 6-year-old boy.

The study highlighted the need for measures to prevent vaccine-related morbidity and mortality in children.

However, an expert panel, including blood cancer specialists, reviewed the case and concluded that there was no causal relationship between the vaccine and the death.

Despite reconfirming the safety of the vaccine, the KDCA acknowledged the higher incidence of shingles following Sky Varicella vaccination compared to other vaccines. Consequently, they emphasized the need for careful vaccination of high-risk groups, such as immunocompromised individuals, and committed to providing detailed guidance on this matter.

The KDCA also highlighted that while live attenuated chickenpox vaccines can cause shingles, the symptoms are generally milder than those resulting from natural chickenpox infection.

The agency urged the medical community to actively report adverse events following vaccination and promised enhanced surveillance and additional diagnostic testing if adverse events are reported.

The MFDS also plans to intensify post-market safety monitoring and long-term effectiveness studies for domestically approved chickenpox vaccines.

The controversy

However, the KDCA's announcement has not been without controversy.

The agency faced criticism for causing unnecessary confusion and exacerbating safety concerns about Sky Varicella as the KDCA had scheduled a briefing to discuss the results of the Immunization Subcommittee's meeting on adverse event reports and safety assessment related to the vaccine on April 26.

However, the briefing was abruptly canceled on the day of the event, with the KDCA stating that additional investigation and analysis were needed due to newly raised issues regarding adverse reactions to the chickenpox vaccine.

This cancellation led to various rumors, including speculations about administrative actions against SK bioscience's vaccine. Concerned parents of young children questioned the safety of the Sky Varicella vaccine, adding to the public anxiety.

The KDCA was unavailable for comments regarding why the announcement was suddenly canceled and what additional investigation and analysis were conducted.