Breakthrough chickenpox is an infection with the varicella-zoster virus (VZV) in individuals previously vaccinated against chickenpox. This condition is milder than chickenpox in unvaccinated people, often presenting with fewer skin lesions and a lower likelihood of fever. For classification, the illness must appear more than 42 days after vaccination. Despite its milder nature, breakthrough chickenpox remains contagious.
Understanding Breakthrough Chickenpox Contagiousness
Breakthrough chickenpox is contagious, often for a shorter duration and with reduced transmissibility compared to typical chickenpox. The virus can spread one to two days before the rash appears. Contagiousness usually continues until all lesions have formed scabs.
If the rash is mild with fewer than 50 lesions, vaccinated individuals are estimated to be about one-third as contagious as unvaccinated people. However, if a breakthrough case develops 50 or more lesions, contagiousness can be similar to an unvaccinated person. When lesions are atypical and do not form scabs, contagiousness persists until no new lesions have appeared for at least 24 hours.
Identifying the Start and End of Contagion
Identifying the beginning of contagiousness can be challenging, as the rash may be the first noticeable sign, often preceded by one to two days of feeling unwell. The rash in breakthrough cases may present as maculopapular (flat or slightly raised bumps) rather than fluid-filled blisters. This atypical presentation can make clinical diagnosis more difficult than with traditional chickenpox.
The end of the contagious period is marked by specific visual cues. For typical chickenpox, contagiousness ceases once all lesions have dried and formed scabs. For breakthrough cases, where lesions may not fully scab, a person is no longer considered contagious when no new lesions have emerged for a full 24-hour period. All existing spots must either be scabbed or the 24-hour new-lesion-free period must have passed.
Minimizing Spread
To prevent the spread of breakthrough chickenpox, several measures are helpful during the contagious period. Individuals should avoid contact with vulnerable populations, including infants, pregnant individuals, and those with weakened immune systems. The virus spreads through airborne respiratory droplets from coughing or sneezing, and direct contact with the rash.
Practicing good hand hygiene, such as frequent handwashing, limits transmission. Covering coughs and sneezes helps contain respiratory droplets. Avoiding scratching lesions is important, as this can spread the virus through direct contact with fluid. Isolation from school or work is generally recommended until no longer contagious. Washing and sanitizing linens and other items that contacted lesions can further reduce transmission risk.