Varicella vaccine facts for kids

Varicella vaccine
Vaccine description
Target disease	Varicella
Type	Attenuated virus
Quick facts for kids Identifiers
CAS number	934490-96-7
ATC code	J07BK01 J07BK02 J07BK03
PubChem	?
DrugBank	DB10318
ChemSpider	none
Therapeutic considerations
Pregnancy cat.	B2(AU)
Legal status	Prescription Only (S4)(AU) POM(UK) ℞-only(US) ℞ Prescription only
Routes	subcutaneous

The varicella vaccine, also called the chickenpox vaccine, is a special medicine. It helps your body fight off the chickenpox virus. This vaccine is given as a shot just under your skin.

One dose of the vaccine can stop 95% of mild cases. It can also prevent 100% of severe chickenpox cases. Getting two doses works even better than one. If you get the vaccine within five days of being around someone with chickenpox, it can often stop you from getting sick. When many people get vaccinated, it also helps protect those who cannot get the vaccine.

The World Health Organization (WHO) suggests countries give this vaccine regularly. But they say it works best if more than 80% of people get it. If only a few people get vaccinated, more adults might get chickenpox. This can be more serious for older people.

The chickenpox vaccine was first made in the 1970s in Japan. A scientist named Michiaki Takahashi led this work. Later, in the United States, Maurice Hilleman helped develop it further. The vaccine became available to buy in 1984. It is now on the WHO Model List of Essential Medicines. This means it is considered a very important medicine.

How the Chickenpox Vaccine Works

The varicella vaccine is very good at preventing chickenpox. It stops 70% to 90% of all cases. It is more than 95% effective at preventing serious chickenpox. Studies in the United States show it protects children for at least 11 years. In Japan, studies found protection for at least 20 years.

Sometimes, people who get the vaccine might still get a mild case of chickenpox. This can happen if they are around someone with the virus. But these cases are usually very mild. People might only show a few signs of being sick. This is called "breakthrough disease."

Another vaccine, called the zoster vaccine, uses a larger dose of the same vaccine. It helps older adults avoid shingles. Shingles is caused by the same virus that causes chickenpox. The zoster vaccine is suggested for adults aged 50 and older.

How Long Does Protection Last?

We don't know exactly how long the chickenpox vaccine protects you. Some people vaccinated 20 years ago are still protected. But others might become vulnerable in as little as six years. It is hard to know for sure when chickenpox is still common. Being around the natural virus can boost a vaccinated person's protection.

Some vaccinated children have lost their protection after five to eight years. But the WHO says that over 90% of healthy people vaccinated as children were still protected after 10 to 20 years. In Japan, many children were not vaccinated. So, vaccinated children often came into contact with the virus. This helped keep their immune systems strong. In the United States, almost all children get vaccinated. This means they don't get natural boosts from the virus. So, booster shots might be needed over time. If you are vaccinated and then get the virus, your chickenpox will likely be milder.

Why Get Vaccinated Against Chickenpox?

Before the vaccine was widely used in the United States in 1995:

• About 4 million people got chickenpox each year.
• Most of these were children.
• Around 10,500 to 13,000 people went to the hospital.
• 100 to 150 people died each year, mostly young children.

After the vaccine became common, these numbers dropped a lot. The number of chickenpox cases fell by 90%. Hospital stays for chickenpox dropped by 71%. Deaths from chickenpox in people under 20 fell by 97%.

The vaccine is less effective for people with weak immune systems. It can also be more risky for them. This is because the vaccine uses a weakened live virus. For example, in one study, 30% of children with weak immune systems lost their protection after five years. Also, 8% of them caught chickenpox during that time.

Chickenpox and Shingles

Shingles usually affects older adults. It is rare in children. The risk of getting shingles is lower for vaccinated children. But the vaccine does not remove the risk completely. The CDC says that the vaccine uses a weakened chickenpox virus. This virus can stay hidden in your body. It might cause shingles later in life. However, the chance of getting shingles from the vaccine virus is much lower. It is much less likely than getting shingles after having natural chickenpox.

The risk of shingles is about 80% lower for healthy vaccinated children. This is compared to unvaccinated children who had chickenpox naturally. When many people in an area are vaccinated, it also helps protect unvaccinated children from shingles. This is called herd immunity.

When to Get the Chickenpox Vaccine

The WHO suggests one or two doses of the vaccine. The first dose is usually given when a child is 12 to 18 months old. If a second dose is given, it should be at least one to three months later. The second dose helps give even better protection. This vaccine is given as a shot under the skin. It is suggested for all children under 13. It is also for anyone 13 or older who has never had chickenpox.

In the United States, the CDC recommends two doses:

• The first dose is given when a child is 12 to 15 months old.
• The second dose is given when they are 4 to 6 years old.
• The second dose can be given as early as 3 months after the first.

If someone misses these times, they can still get "catch-up" vaccinations:

• Children aged 7 to 12 years should get two doses, 3 months apart.
• People aged 13 to 18 years should get two doses, 4 to 8 weeks apart.

In the UK, the vaccine is not given to everyone. It is mainly for people who are close to someone very vulnerable to chickenpox. The UK government worries that if fewer children get chickenpox, more adults might get it. Chickenpox is usually more serious for adults. However, the vaccine is approved for children 12 months and older. You can get it privately, with a second dose a year after the first.

Who Should Not Get the Vaccine?

The varicella vaccine is not for everyone. It is not suggested for:

• People who are very sick.
• Pregnant women.
• People with tuberculosis.
• Anyone who had a serious allergic reaction to the vaccine before.
• People allergic to gelatin or neomycin.
• People taking high doses of steroids.
• People getting cancer treatment like x-rays or chemotherapy.
• Anyone who has had blood products or transfusions in the last five months.
• People taking salicylates (like aspirin). You should avoid salicylates for at least six weeks after the vaccine.
• People who got another live vaccine in the last four weeks.

However, it might be safe for some people with HIV/AIDS if their blood counts are good and they are getting proper treatment. Also, specific antiviral medicines should not be taken 24 hours before and 14 days after the vaccine.

Possible Side Effects

Serious side effects from the vaccine are very rare. Between 1998 and 2013, only one death linked to the vaccine was reported. This was an English child with a serious blood condition. Very rarely, severe reactions like meningitis (brain swelling) and pneumonia (lung infection) have been reported. These mostly happened in children with weak immune systems who should not have received the vaccine. Serious allergic reactions (like anaphylaxis) are also very rare.

Mild side effects can include:

• Redness, stiffness, or soreness where the shot was given.
• A mild fever.
• A small rash around the injection site.

There is a small chance of getting herpes zoster (shingles) after the vaccine. But this risk is much lower than getting shingles after having natural chickenpox. Most cases of shingles after vaccination are mild.

About 5% of children who get the vaccine might have a fever or rash. From 1995 to 2005, about 55.7 million doses were given. No deaths were linked to the vaccine during this time. Some people with weak immune systems have gotten vaccine-related chickenpox, but no deaths were reported.

History of the Vaccine

The chickenpox vaccine is made from a weakened form of the varicella virus. This special virus strain is called the Oka strain. It was first found in a child with natural chickenpox. Then, scientists grew it in different types of cells.

Michiaki Takahashi and his team in Japan developed the first live weakened varicella vaccine in the early 1970s. Later, companies like Merck & Co. and GlaxoSmithKline helped improve it. In 1981, Maurice Hilleman's team at Merck used the Oka strain to make a chickenpox vaccine.

Japan was one of the first countries to vaccinate against chickenpox. The vaccine made by Hilleman was first approved in the United States in 1995. Since then, the number of chickenpox cases in the US has dropped a lot. It went from 4 million cases per year to about 390,000 cases per year by 2014.

As of 2019, chickenpox vaccines are available in all 27 countries of the European Union. Sixteen of these countries also offer a combined vaccine called measles, mumps, rubella, and varicella vaccine (MMRV). Twelve European countries recommend that all children get the chickenpox vaccine. These countries have seen fewer chickenpox cases and hospital stays.

In Canada, the varicella vaccine is recommended for all healthy children aged 1 to 12. It is also suggested for adults up to 50 years old who have not had chickenpox. It can also be considered for people with certain immune problems.

Australia also recommends regular chickenpox shots for children and adults.

Other countries, like the United Kingdom, only recommend the vaccine for certain groups. For example, healthcare workers who might be around chickenpox. In the UK, pregnant women are checked for chickenpox protection. By 2005, all healthcare workers in the National Health Service were checked and vaccinated if needed. But the UK does not give the vaccine to everyone.

Since 2013, the MMRV vaccine is free for all citizens in Brazil.