What does the measles vaccine contain?

In the 1950s, measles affected 3 to 4 million individuals annually in the United States. A vaccine for this highly contagious respiratory illness was created in 1963, and by 2000, it had been largely eradicated in the U.S. However, the disease continues to spread among those who are unvaccinated. A major outbreak in Ohio’s Amish community last year led to over 300 infections, and another incident at Disneyland in California last month has resulted in more than 100 cases across 14 states, mainly among children whose parents oppose vaccination.

Merck, a pharmaceutical company, produces the measles vaccine in the U.S. The vaccine, which also protects against mumps and rubella (German measles), is known as MMR II. Each 0.5-milliliter dose contains 10 ingredients. We spoke with Vincent Racaniello, a microbiology and immunology professor at Columbia University, to understand the specific components and their purposes. Racaniello has been studying viruses for over 35 years.

Ingredients

Measles Virus To create a vaccine for a virus-caused disease, scientists begin by growing the virus in a laboratory. 'Every vaccine varies, but the process generally starts with cells growing in a plastic dish with a liquid medium on top,' explains Racaniello. 'The cells become infected with the virus, and after a few days, the virus multiplies. The liquid medium, where the virus resides, is then collected and used for the vaccine.'

The measles strain used in the vaccine, called Edmonston, is derived from the original 1960s version. Scientists cultivate the virus using chick embryo cells. The growth medium, called Medium 199, is a salt solution enriched with vitamins, amino acids, fetal bovine serum, sucrose, phosphate, glutamate, neomycin, and recombinant human albumin (more details on these ingredients below).

Mumps Virus Mumps is cultivated in the same way as measles: using chick embryo cell cultures and the Medium 199 liquid medium for growth.

Rubella Virus Unlike measles and mumps, rubella is cultivated using human diploid lung fibroblast cells known as WI-38. 'This cell line has been around for decades,' says Racaniello. 'It was created once, and these cells continue to grow in cultures indefinitely. They are stored in the lab freezer, so there’s no need to collect human lungs every time a vaccine is made.'

Rubella is cultured in Minimum Essential Medium, a salt solution containing vitamins, amino acids, fetal bovine serum, recombinant human albumin, and neomycin.

Sorbitol Sorbitol serves as a stabilizer and is commonly used as an artificial sweetener in food. 'It’s included in the vaccine to prevent the viruses from breaking down during handling,' explains Racaniello.

Sodium Phosphate Sodium phosphate, a type of salt, acts as a buffer to stabilize the vaccine’s pH level when it is frozen or thawed. 'Vaccines are delivered frozen to hospitals and doctors,' says Racaniello. 'When thawed, the pH can shift, which could affect the virus’s ability to infect. Sodium phosphate helps maintain the vaccine’s pH at 7, the desired level.'

Sucrose Sucrose, or sugar, is an ingredient in the liquid growth medium used to cultivate the cells. It provides energy for the cells. 'The growth medium supplies the cells with necessary nutrients,' Racaniello says. 'Since the vaccine is derived from this medium, those components are also present in the vaccine.'

Sodium Chloride Sodium chloride, another form of salt, is also sourced from the cell culture medium. 'It ensures the medium is isotonic,' Racaniello explains. 'Cells contain a specific amount of salt, and the medium must match. This is similar to when you receive an intravenous drip with saline, which is matched to your body fluids. Sodium chloride ensures the composition of the culture medium aligns with the cells used to grow the viruses.'

Hydrolyzed Gelatin Hydrolyzed gelatin, like sorbitol, is a stabilizer that ensures the viruses remain infectious. 'Gelatins are long-chain molecules,' Racaniello says. 'Hydrolyzed means they’ve been broken down into smaller components, which makes them more effective as stabilizers.'

Recombinant Human Albumin This protein is another ingredient in the cell culture medium, essential for proper cell growth. 'Human albumin is naturally found in blood,' says Racaniello. 'Recombinant means it’s produced in a highly purified form, free from contaminants.' To produce it, scientists insert the human albumin gene into a cell and grow it in the lab. Once the cell generates the albumin, scientists extract and purify it directly from the cell, avoiding the need to extract it from blood, which could introduce contaminants.

Fetal Bovine Serum Fetal bovine serum, collected from cow blood, is another component carried over from the cell culture medium. 'It’s rich in growth factors,' explains Racaniello. 'We don’t fully understand all the growth factors needed for cells to thrive in culture. If we did, we could synthesize them in a lab and mix them together. That’s why we still rely on animal-derived serum for this purpose.'

The ingredients in the vaccine support its growth in the lab and help maintain its stability in the vial. But what happens to these ingredients once the vaccine is injected into your body?

The MMR vaccine is usually administered subcutaneously, where it begins to diffuse into the tissues and reach the lymphatic system. 'The lymphatic system consists of highly permeable capillaries that absorb anything circulating in the tissues,' says Racaniello. The vaccine then travels to a lymph node, which houses immune cells. When these cells detect a foreign substance, such as the viruses in the vaccine, an immune response is triggered. 'If you get a sore arm after the shot, that’s a sign your immune system is reacting to the vaccine's components,' says Racaniello. 'This is a good sign because it shows that the vaccine is working.'

Eventually, the virus spreads throughout your body. 'These are live viruses, so they replicate in specific cells, producing more viruses and prompting a strong immune response,' Racaniello explains. 'That’s why vaccines are so effective: because they use infectious viruses.' The viruses your body produces won’t cause measles, mumps, or rubella, but they will stimulate your immune system to produce antibodies that can fight off future infections. If you ever encounter measles, mumps, or rubella, your body will already be prepared to defend against them.

The other components of the vaccine quickly spread throughout your body within minutes. 'All of these elements are rapidly diluted, so you won’t even notice they’re there,' says Racaniello. 'Vaccines are a powerful tool in preventing diseases. This particular vaccine has been in use for many years, and it’s unfortunate that more people aren’t taking advantage of them as they should. These infections can be deadly.'

Sources: CDC, Merck, Dr. Vincent Racaniello, Higgins Professor in the Department of Microbiology & Immunology, Columbia University