Attenuated vaccine

An attenuated vaccine is a special kind of vaccine made by weakening a germ so it can’t make you sick anymore, but it’s still alive enough to teach your body to fight it. This process of weakening the germ is called attenuation. Unlike other vaccines that use a germ that has been completely killed, attenuated vaccines use a germ that is still alive but much weaker.

These vaccines are very good at helping your body build strong and lasting protection. They often work faster and better than vaccines made from killed germs. However, they are not given to people who are pregnant or who have weak immune systems, because their bodies might not handle the live germ safely.

Attenuated vaccines work by prompting your body to make special defense cells called antibodies and memory immune cells. These cells remember the germ and can fight it off quickly if you are exposed to it later. Some common attenuated vaccines protect against diseases like measles, mumps, rubella, yellow fever, varicella, and certain types of influenza.

Development

Viruses can be made weaker but still alive to create vaccines. This is done by passing the virus through a different host, like chicken eggs or lab-grown tissue. Over time, the virus changes and becomes less harmful, helping the body build protection without causing sickness.

Bacteria can also be weakened in a similar way, sometimes by changing their genes to make them safer. This helps the body learn to fight the bacteria without getting very ill.

Administration

Attenuated vaccines can be given in different ways. They can be injected under the skin or into the skin for diseases like measles, mumps, rubella, varicella, tuberculosis, and smallpox. They can also be given through the nose for influenza or through the mouth for diseases like polio, cholera, typhoid, and rotavirus.

These vaccines are usually given to people older than 12 months, except for the rotavirus vaccine, which can be given at 6 weeks old.

Mechanism

Vaccines help our bodies fight germs by creating special cells and molecules, like CD8+ and CD4+ T lymphocytes, or antibodies. These can stop or lessen infections by removing infected cells or making interleukins.

Attenuated vaccines are weaker versions of germs, such as viruses or bacteria. They are changed so they can't make us sick but still tell our immune system there's a problem. This helps our body prepare to fight the real germ. This type of vaccine gets our immune system ready in two ways, helping both parts of our defenses work well.

Safety

Live-attenuated vaccines are safe and help the body build a strong, lasting defense against diseases. Because the germs in these vaccines are weakened, it is very unlikely for them to become strong again and make someone sick. For the five main live-attenuated vaccines recommended by the World Health Organization — tuberculosis, oral polio, measles, rotavirus, and yellow fever — serious side effects are very rare.

People whose bodies have trouble fighting off infections, such as those with certain health conditions, usually should not get live-attenuated vaccines. However, family members of these individuals can still get the vaccines, except for the oral polio vaccine. As a extra safety step, these vaccines are not usually given to women who are pregnant, to protect the baby. Some vaccines, like the nasal flu vaccine, might cause mild issues like a runny nose.

Live-attenuated vaccines need special care to stay effective, such as being kept cool during travel and handling.

History

The history of vaccines began with Edward Jenner in the late 1700s. He found that using a harmless version of a virus from animals could protect people from the deadly smallpox disease. Later, Louis Pasteur discovered how to weaken harmful germs and used this method to create a vaccine for anthrax. He and his team also made the first rabies vaccine.

In the early 1900s, scientists Albert Calmette and Camille Guérin developed a weakened version of the tuberculosis germ, called the BCG vaccine. Their work helped create better ways to make vaccines, such as growing germs in labs instead of animals. This led to many successful vaccines in the middle of the 20th century, including ones for polio, measles, mumps, and rubella.

Advantages and disadvantages

Attenuated vaccines have many good points. They act a lot like real infections, helping the body learn to fight off the disease. They can create strong protection that lasts a long time, sometimes for life, and often just one or two doses are needed. They are also usually cheaper than other health treatments.

But there are some downsides too. Very rarely, the weakened virus might change back to a stronger form, especially if not many people are vaccinated. They aren’t usually suggested for women who are pregnant or for people whose bodies can’t fight off infections well. Also, these vaccines often need special care, like being kept cool, which can make it hard to get them to places far away.

List of attenuated vaccines

Currently in-use

Bacterial vaccines

• Anthrax vaccine
• Cholera vaccine
• Plague vaccine
• Salmonella vaccine
• Tuberculosis vaccine
• Typhoid vaccine

Viral vaccines

• Live attenuated influenza vaccine (LAIV)
• Japanese encephalitis vaccine
• Measles vaccine
• Mumps vaccine
• Measles and rubella (MR) vaccine
• Measles, mumps, and rubella (MMR) vaccine
• Measles, mumps, rubella and varicella (MMRV) vaccine
• Polio vaccine
• Rotavirus vaccine
• Rubella vaccine
• Smallpox vaccine
• Varicella vaccine
• Yellow fever vaccine
• Zoster/shingles vaccine

In development

Bacterial vaccines

• Enterotoxigenic Escherichia coli vaccine

Viral vaccines

• Tick-borne encephalitis vaccine
• COVID-19