The shingles vaccine sold today, Shingrix, contains a lab-made protein from the varicella-zoster virus paired with a powerful immune-boosting system called AS01B. Each 0.5 mL dose delivers 50 micrograms of this viral protein along with two immune enhancers, several stabilizers, and a handful of buffering salts. It does not contain a live or weakened virus, and it has no preservatives.
The Active Ingredient: A Single Viral Protein
The core ingredient is a protein called glycoprotein E (gE), which sits on the surface of the varicella-zoster virus. Rather than using the actual virus, Shingrix is made by inserting the gene for this protein into lab-grown cells, which then produce it in large quantities. Your immune system recognizes glycoprotein E as a threat and builds a targeted defense against the virus that causes shingles.
This recombinant approach is what makes Shingrix fundamentally different from the older shingles vaccine, Zostavax, which used a live but weakened form of the virus and has since been discontinued in the U.S. Because Shingrix contains only a single protein and no live virus, it’s safe for people with weakened immune systems.
The Adjuvant System: AS01B
A protein on its own wouldn’t trigger a strong enough immune response, especially in older adults whose immune systems have slowed down. That’s the job of AS01B, the adjuvant system that makes up a significant portion of the vaccine. It contains two immune enhancers, each dosed at 50 micrograms per shot:
- MPL, a chemically detoxified molecule originally derived from a type of Salmonella bacteria. It activates a specific receptor on immune cells (Toll-like Receptor 4), essentially sounding an alarm that tells the body to pay attention to what’s in the vaccine.
- QS-21, a compound purified from the bark of a South American tree called Quillaja saponaria. It activates a different part of the immune system’s early-warning network, triggering an inflammatory signaling complex that amplifies the response.
These two enhancers are packaged inside tiny fat bubbles called liposomes, made from a phospholipid (DOPC, at 1 mg per dose) and cholesterol (0.25 mg per dose). The liposomes help deliver the immune enhancers to the right cells and keep the components stable.
Buffers, Stabilizers, and Other Inactive Ingredients
The remaining ingredients serve practical roles: keeping the vaccine at the right pH, preventing the protein from breaking down, and ensuring the components stay evenly mixed. Each dose contains:
- Sucrose (20 mg): a sugar that stabilizes the protein during storage
- Sodium chloride (4.385 mg): ordinary salt, used as a buffer
- Potassium dihydrogen phosphate (0.54 mg) and disodium phosphate anhydrous (0.15 mg): phosphate salts that maintain pH
- Dipotassium phosphate (0.116 mg): another pH buffer
- Polysorbate 80 (0.08 mg): an emulsifier that keeps ingredients from separating
- Water for injection: the liquid base
Shingrix contains no thimerosal (mercury-based preservative), no other preservatives, and no natural rubber latex in its packaging.
How These Ingredients Work Together
When Shingrix is injected into your upper arm, the glycoprotein E gives your immune system a clear target. The two AS01B components create a temporary burst of immune activation at the injection site, drawing in immune cells and pushing them to respond aggressively to that protein. The result is both antibodies (which can neutralize the virus directly) and specialized T cells (which can hunt down and destroy virus-infected cells).
This combination is why Shingrix works so well even in older adults. In clinical trials, the vaccine was 96.6% effective at preventing shingles in adults aged 50 to 59, 97.4% effective in adults 60 to 69, and still above 91% effective in people 70 and older. A large study of nearly two million people published in Annals of Internal Medicine found the vaccine remained 73% effective four years after the second dose.
The Two-Dose Schedule
Shingrix is given as two separate injections. For most adults 50 and older, the second dose comes two to six months after the first. People who are immunocompromised (due to conditions like HIV, certain cancers, or medications that suppress the immune system) can receive the vaccine starting at age 19, and their second dose can be given as early as one to two months after the first to build protection faster.
Both doses are necessary. The first primes your immune system; the second strengthens and extends that protection significantly.
Common Side Effects and Why They Happen
The AS01B adjuvant is deliberately designed to provoke a strong immune reaction, which is why side effects from Shingrix tend to be more noticeable than with many other vaccines. About 78% of people report pain at the injection site. Roughly 1 in 10 experience more widespread reactions like muscle pain, fatigue, headache, shivering, fever, or stomach upset. These symptoms typically reflect the immune system responding vigorously to the vaccine and generally resolve within two to three days.