There are several types of HPV, including the type 16 is the strain that causes almost 50% of cervical cancer and four other strains can also cause cancer. Cervical cancer may occur after cells in the cervix undergo changes due to persistent HPV infection by a single strain of the virus.
Vaccines have made important historic strides in public health, nearly eradicating devastating diseases such as smallpox and polio. The new HPV vaccine is the first approved anticancer vaccine and is currently under much scrutiny.
This vaccine, called Gardasil or Cervarix, has been aggressively marketed and even proposed as mandatory vaccination for females between the ages of nine and 26 years. It protects against four types of HPVs that may cause 70 percent of cervical cancers; however, the vaccine's long term effects are not yet known. Protection is thought to last up to four years and further studies are required to assess whether booster shots are needed after this period.
The vaccine does not provide immunisation against other HPV strains that can cause 30 percent of cervical cancers and it cannot cure existing infections. Females still require regular pelvic exams and Pap screen tests even after vaccination. Doctors are concerned that this vaccination may deter females from getting Pap tests, which is a tried and tested method of preventing cervical cancer.
Like all medication, vaccines carry some risks. Though extremely rare, these risks include complications such as potentially fatal blood clots. The HPV vaccine is also painful and side effects may include nausea and dizziness. Though it has been successful in preventing HPV infections, long term studies done over time are needed to determine whether the HPV vaccine prevents cervical cancer. Individuals with underlying medical conditions should be assessed by their doctor before receiving the HPV vaccination.
The HPV vaccine is an inactivated or killed vaccine. Noninfectious killed virus vaccines are designed to work without causing infection in the recipient. The polio vaccine is an example of this type. This method of making vaccines was first developed by treating the polio virus with formaldehyde to disable it, so that it cannot infect the body but still appears to be a live virus to the immune system. The common flu vaccine and vaccines against bacterial infections such as typhoid and pertussis or whooping cough are made with a similar process.
Another method to make non-infectious vaccines uses parts of the pathogens. A vaccine made with this method contains only the part of the virus or bacteria that the immune system recognizes such as the cell wall. In this way the immune system still builds up antibodies for immunity against the disease even though the body is not actually infected.
Written by Mark Riegel, MD
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