Christmas party revelry is only weeks away - and with it the high spirits that contribute every year to a marked increase in sexually transmitted diseases. Even during the Second World War seasonal jollity resulted in a rise in the (already increased) rate of STDs.

Doctors are wondering what the effect of the credit crunch will be on new year queues at genito-urinary clinics. Specialists in this area have noticed that some City workers, the first to feel the effects of recession, have suffered physically as well as financially. The pattern of graphs showing the decline in share prices could be mirrored by another showing the increase in sexually transmitted infections. Will more anxiety - induced by fear of unemployment, forced house sales, unpaid school fees and rocketing fuel bills - drive the depressed and insecure to escape grim reality with an exciting if transient affair and a visit to the clinic?

When people think of sexually transmitted infections they generally take the term to mean gonorrhoea, chlamydia, herpes and, for a very unfortunate few, HIV or syphilis. Other problems may also be spread sexually but, as they can be transmitted in various other ways, they tend to be overlooked. Trichomonas vaginalis, bacterial vaginitis, genital warts and even thrush and cystitis may be linked to relatively innocent sexual behaviour and treated in GPs' surgeries rather than specialist clinics, but it is undeniable that these troubles are uncommon in dutiful nuns.

One sexually transmitted infection with which about 70 per cent of sexually active people are, often unknowingly, confronted at some time, but usually throw off without lasting complications, is HPV, the human papillomavirus. HPV is popularly known as the genital wart virus, but this term irritates doctors who specialise in cervical cytology. They always refer to it as HPV and emphasise that although there are 80 HPV strains only two of these - HPV 16 and 18 - are responsible for about 75 per cent of cervical cancer cases. Another 11 strains of HPV have been shown to cause such tumours occasionally. Two other strains of HPV - 6 and 11 - result in unsightly genital warts, an affliction that frequently necessitates regular attendance at hospital clinics.

Once a cervical smear has been taken by the doctor or nurse at a clinic or surgery it is analysed for any abnormalities in its cells. These changes will be classified into three groups, CIN1, CIN2 and CIN3, depending on the severity of the problem. The last category, CIN3, is officially recorded as carcinoma in situ - pre-cancerous changes confined to the cell. Each year about 3,000 cases of cancer of the cervix that has become embedded and is beginning to spread are diagnosed; of these patients, about 1,000 die as a result of the condition. Some 17,000 cases of CIN3 are detected during routine screening and two thirds of these would progress to cancer if not treated. The remarkable success of screening and treatment is reflected in these figures, but the number of women attending to have smears taken is falling.

As 99.7 per cent of all cases of cervical cancer can be shown to have resulted from HPV infection, and more than 75 per cent of sexually active women have at some time been infected by HPV, the search for a vaccine that would spare women this hazard was intense.

Two vaccines have been licensed for use in this country. The one selected for the government vaccination campaign - and for the private scheme at Boots - is Cervarix. This protects against HPV strains 16 and 18, the two types usually responsible for cancer. The other vaccine is Gardasil, which not only protects against HPV 16 and 18 but also guards against 6 and 11, the strains that cause genital warts. There has been a suggestion that possibly it won't provide quite such lasting protection as Cervarix against 16 and 18.

Vaccination is offered early to girls, at about 12 or 13, as by that age 10 per cent of them are sexually active. Realism, and the results of immunity tests, have persuaded the authorities and most parents and doctors that to wait longer is unwise. Once a girl is infected, vaccination gives no extra protection against cancer but may prevent infection from the other strain of HPV.

As no steps are being taken to vaccinate men, there is a danger that HPV could come to be regarded as solely a female problem. But HPV is also responsible for penile cancer, anal cancer and - importantly - 47 per cent of cases of head, neck and mouth cancer.

The incidence of these cancers is rising alarmingly. Vaccinating boys as well as girls would protect both sexes not only from nasty below-the-belt cancers but from some unpleasant tumours above the collar. Vaccination of boys would also probably reduce the risk of men later handing on HPV to their sexual partners.