OBJECTIVES : Argentina introduced one-dose universal varicella vaccination (UVV) in 2015. The objective of this study was to use a dynamic transmission model to evaluate both the impact of this programme and the implications of dosing schedules and vaccine characteristics on the short and long-term impact of UVV in a future two-dose schedule.

METHODS : We used the only available historical (1996) seroprevalence data from Argentina to calibrate a dynamic transmission model of varicella infection in a static population. In addition to the current one-dose UVV administered at 15 months, we considered two-dose UVV with different dosing intervals: short (15 and 18 months); medium (12 and 18 months); and long (15 months and 6 years). In all cases, we assumed coverage would be 90% with 1^st dose and 85% with 2^nd dose. We evaluated these scenarios considering two hypothetical varicella vaccines: a highly-effective vaccine with long duration of protection and a moderately-effective vaccine with shorter duration of protection.

RESULTS : The estimated pre-vaccine varicella incidence of approximately 1,375 cases per 100,000 population per year will reduce to between 20-50 cases per 100,000 after two years of high-coverage (90%), single-dose UVV, depending on the vaccine used. Use of a two-dose UVV programme can prevent over 60 million varicella cases and 8,000 deaths over 100 years; the most effective programme is the short interval with the highly-effective vaccine, which prevents 500,000 cases and 52 deaths more than the least-effective programme (the moderately-effective vaccine with a long interval between doses). The differences in outcomes between the vaccines were most pronounced for long intervals between doses, and least pronounced for short intervals between doses.

CONCLUSIONS : Two-dose UVV in Argentina has the potential to significantly reduce varicella incidence. Based on the historical seroprevalence data, a short or medium interval between doses with a highly-effective vaccine prevents the most disease.