If your child has already had one chickenpox vaccination, you may wonder why another dose is recommended.
One dose gives good protection. Two doses give better, longer-lasting protection. The second dose helps strengthen the body’s response and protects more children.
What does the first dose do?
The chickenpox vaccine teaches the immune system how to recognise and fight the virus.
Most children respond well to the first dose, but some do not develop a strong enough response. This means they may still catch chickenpox if exposed.
Having one dose does not mean your child has no protection. It means their protection may be less complete than after two doses.
How does the second dose help?
The second vaccination gives the immune system another opportunity to build protection.
It helps children who did not respond fully to the first dose and strengthens the overall response.
Think of the first dose as the introduction and the second as a reminder that helps the body prepare more effectively.
How effective are two doses?
The UK Green Book reports that two doses of the chickenpox-only vaccine provide around 98% protection in children.
It also describes a study that estimated protection against chickenpox at:
93% after one dose
97% after two doses
These figures come from different studies, so estimates vary. The consistent finding is that two doses protect better than one.
What about the combined MMRV vaccine?
MMRV protects against measles, mumps, rubella and varicella—the medical name for chickenpox.
The Green Book reports that approximately 87% of children develop chickenpox antibodies after one MMRV dose, increasing to approximately 99% after the second dose.
Antibodies are part of the body’s defence against infection. These antibody figures measure the immune response; they are not the same as the percentage guaranteed never to catch chickenpox.
Can a vaccinated child still catch chickenpox?
Yes. No vaccine provides complete protection for everyone.
However, chickenpox after vaccination is usually milder, with fewer spots and fewer general symptoms. A child who develops chickenpox can still pass it to others.
My child has only had one dose. What should I do?
Ask a healthcare professional to check your child’s vaccination record.
The advice depends on their age, which vaccine they received, when it was given and whether they have previously had chickenpox. NHS schedules and catch-up arrangements differ between age groups, so having one recorded dose does not automatically mean an appointment has been missed.
Speak to Trustwell Clinic
Unsure whether your child needs another chickenpox vaccination? Contact Trustwell Clinic to discuss their vaccination history and the appropriate next step. Have their vaccination record available so the clinician can check what they have already received.
Source: UK Green Book, Chapter 34: Varicella, April 2026. All clinical information and figures in this article are drawn from this chapter.