Benefits outweigh risks of HPV vaccination

Benefits outweigh risks of HPV vaccination

Vaccination has been medicine's boon for mankind as it has virtually eradicated many infectious diseases. The classical example is smallpox, which now only exists in certain laboratories.

The incidence of some infectious diseases have decreased considerably with vaccination, for example, since the World Health Organization (WHO)'s launching of the Global Polio Eradication Initiative in 1998, infections have decreased by about 99%, saving about five million people from paralysis.

Newer vaccines have contributed to protection against more infectious diseases, eg the hepatitis B vaccine introduced about two decades ago helped in the prevention of liver cirrhosis and cancer.

The human papilloma virus (HPV) vaccine which helps in the prevention of HPV infection, a leading causative factor of genital warts and cervical cancer, became available in 2006.

Although Malaysia started its national HPV vaccination programme in 2010, certain quarters still have reservations. This article was written to enable parents and vaccinees to make an informed decision.

Human papilloma virus

Human papilloma virus (HPV), a DNA virus, is a common sexually transmitted infection. There are different HPV types. The cutaneous types cause non-cancerous warts (papillomas), which affect the hands and feet. These types differ from the mucosal types that affect the mouth, respiratory tract, and genitalia, ie penis, vulva, vagina, cervix and anus.

Many HPV types are transmitted sexually. The low risk types, eg HPV 6 and 11, cause benign genital warts and recurrent respiratory papillomas, while persistent infection with high-risk types, eg HPV 16 & 18, is associated with an increased risk of developing high grade cervical intraepithelial neoplasia (CIN), which is a precursor of cervical cancer.

HPV is a major cause of genital warts and cervical cancer. HPV infections by the high risk types are common in young, sexually active women and men. Most clear spontaneously without ever causing CIN, while some develop a persistent infection.

Hence, cervical cancer is considered a rare consequence of persistent infection with one or more high risk types, with other factors playing a role.

HPV 16 and 18 together account for up to 70% of cervical cancers across the world. Other high risk types like HPV 31, 33 and 45, are also associated with cervical cancer.

HPV infections are more likely to occur in people who have more than one sexual partner or whose sexual partner has more than one partner.

Factors like smoking, multiple sexual partners, having many children, oral contraceptive use and HIV infection are associated with an increase in the risk of developing cervical cancer.

HPV also causes cancers of the vulva, vagina and anus.

It is also a cause of recurrent respiratory papillomas (RRP), which is uncommon but potentially life threatening, with serious risk of airway obstruction, particularly in children. Some RRP may become cancerous, especially those due to HPV type 11.

As HPV may have no symptoms, it may be more common than is thought.

There is no published data on the prevalence of HPV infection in the country although the infection is diagnosed sufficiently often enough for such studies to be carried out.

However, there is data on cervical cancer, which is the second most common cancer in women. According to the National Cancer Register for 2003, the overall incidence in Peninsular Malaysia is 16.5 per 100,000 women, with an incidence of 14.6 and 57.8 per 100,000 women in the age groups 30 to 49 and 50 to 69 years respectively.

HPV vaccines

HPB vaccines

Women who had previously been infected by a particular HPV type are unlikely to get re-infected by the same type. This is because the antibodies produced are targeted against the major HPV protein, blocking the interaction between infectious HPV and their epithelial receptors, thereby preventing viral access to the epithelium.

There are two types HPV vaccines, ie bivalent (HPV 16 and 18) and quadrivalent vaccines (HPV 6, 11, 16 and 18). Both contain inactivated extracts from HPV. This means that it does not cause HPV or any conditions that HPV causes. Both vaccines provide protection against 70% of the HPV types that cause cervical cancer.

In addition, the quadrivalent vaccine also provides protection against 90% of the HPV types that cause genital warts, and HPV types that cause cancers of the vulva, vagina and anus.

HPV vaccines do not provide protection against the HPV types that a person has been exposed to. However, a person who has had HPV may still benefit from the vaccine because most people are not infected with all the types of HPV contained in the vaccine.

HPV vaccines also do not provide protection against other sexually transmitted infections (STI). This means that even after vaccination, safe sexual practices, including the use of condoms, are needed to prevent STIs.

HPV vaccination is no substitute for cervical screening. Those who have received HPV vaccines should continue cervical screening.

Safety

Safety

Close monitoring by drug regulatory authorities worldwide have reported that both vaccines are safe. They are generally well tolerated and reactions are minimal.

The Centre for Disease Control (CDC) and the Food and Drug Administration (FDA) of the United States monitor closely the safety of HPV vaccines with three systems that monitor adverse events already known to be caused by vaccines and detect rare adverse events that were not identified during pre-licensure clinical trials.

The systems are the Vaccine Adverse Event Reporting System (VAERS), an early warning public health system that helps CDC and FDA detect possible side effects or adverse events following vaccination, the Vaccine Safety Datalink Project, and the Clinical Immunization Safety Assessment Network, which are collaborations with health care organisations in the US that monitor, evaluate and conduct research on adverse events that might be caused by vaccines.

As of June 22, 2011, approximately 35 million doses of the quadrivalent vaccine were distributed in the US and VAERS received a total of 18,727 reports of adverse events i.e. 0.0535%, following vaccination.

Of the total number of VAERS reports, 92% were considered non-serious, and 8% (i.e. 0.00428% of the total) were considered serious, ie reports of hospitalisation, permanent disability, life-threatening illness, congenital anomaly, or death.

Of the 32 death reports confirmed, there was no unusual pattern or clustering to the deaths that would suggest that they were caused by the vaccine and some reports indicated a cause of death unrelated to vaccination. (www.cdc.gov/vaccinesafety/vaccines/hpv accessed 1 September 2011)

There is a similar statement from the medicines and health care products regulatory agency (MHRA) of the United Kingdom about the bivalent vaccine, ie "To date, the vast majority of suspected adverse reactions reported to the MHRA ... have related to recognised side effects already listed in the product information, were due to the injection process and not the vaccine itself (i.e. 'psychogenic' in nature), or were events that occur commonly in the population receiving the vaccine (adolescent females)." (www.mhra.gov.uk accessed September 1, 2011)

Effectiveness

Effectiveness

Reports on the effectiveness of the vaccine on cervical abnormalities and genital warts have emanated from Australia, which was the first country in the world to introduce a nationally funded HPV vaccination programme with mass vaccination of adolescent girls in 2007 using the quadrivalent HPV vaccine.

Brotherton et al's study on the "Early effect of the HPV vaccination programme on cervical abnormalities in Victoria" reported: "Our study is the first to report the effect of a national human papillomavirus vaccination programme on cervical abnormalities at a population level. With data from a state-based cervical screening register, we have shown a decrease in high-grade cervical abnormalities in young women after the implementation of the vaccination programme." (Lancet 2011; 2085-2092)

Donovan et al's study on "Quadrivalent HPV vaccination and trends in genital warts in Australia" reported: "Before the vaccine programme started, there was no change in the proportion of women or heterosexual men diagnosed with genital warts.

After vaccination began, a decline in number of diagnoses of genital warts was noted for young female residents (59%). No significant decline was noted in female non-residents, women older than 26 years in July 2007, or in men who have sex with men. However, proportionally fewer heterosexual men were diagnosed with genital warts during the vaccine period (28%), and this effect was more pronounced in young men." (Lancet Inf Dis 2011; 39-44)

Vaccination of males

Both HPV vaccines were initially licensed for females. In October 2009, the FDA also licensed the quadrivalent vaccine for males and the American Advisory Committee on Immunization Practices made a recommendation for its use in males.

These decisions were based on studies which showed that the quadrivalent HPV vaccine is highly effective in reducing external genital lesions in young men.

Although the protective efficacy of HPV vaccination in males depends on the outcome of public policy discussions and cost-effectiveness studies, there may be a sound rationale for vaccinating adolescent boys, similar to adolescent girls, at an age when they have had limited or no prior sexual activity.

Sexual activity

Sexual activity

Another argument against HPV vaccines is that they may encourage sexual activity in adolescents or to engage in unsafe sexual practices, and that abstinence is a better solution. This argument is not supported by evidence.

Data from the confidential enquiries into maternal deaths reveal that there are about 67,000 to 75,000 babies born to mothers under 15 years of age annually.

A survey of 4,500 students aged 12 to 19 years in Negri Sembilan reported that 5.4% reported that they have had sexual intercourse and that the mean age of first sexual intercourse was 15 years. (Singapore Med J 2006; 47(6):476-481)

Decisions about sexually activity are complex with multiple influences. The argument that the HPV vaccine will tip the scales toward sexual debut is not only simplistic but naive. Vaccination provides protection against specific diseases. Like all things in life, there may be side effects and risks, which are very much less than that of the disease itself. Based on current evidence, the benefits of HPV immunisation far outweigh the risks, which are minimal.

As HPV infection is a major cause of genital warts and cervical cancer, vaccination offers the hope of a reduction in the incidence of both conditions. However, other measures are needed to eradicate cervical cancer. They include widespread cervical screening and safe sexual practices.

Reports on the reduced frequency of genital warts and high-grade cervical abnormalities following HPV vaccination are very encouraging. Readers can seek further clarifications from their regular doctor.

Dr Milton Lum is a member of the board of Medical Defence Malaysia. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organization the writer is associated with.

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