Women in Hong Kong are facing months of delay in getting vaccinated against human papilloma virus, or HPV, because of a drug shortage, and authorities are receiving a flood of complaints. The virus is a major cause of cervical cancer.

Private clinics in the city have been canceling appointments and blocking new patients looking to get vaccinated, some since April.

The shortage has triggered a raft of complaints to the Hong Kong Department of Health and the Consumer Council, the city's consumer rights watchdog, mostly from mainland residents who have traveled to the city only to find they can no longer get an injection.

As of Oct 18, the Consumer Council had recorded 281 complaints about vaccine services, 11 times more than last year. Most were related to the HPV vaccines.

The vaccines - Cervarix and Gardasil - are administered in a series of three shots, and manufacturers recommend that a full course be completed within six months. However, the shortage means many women will have to wait much longer.

Xu Cen, 30, from Shenzhen, Guangdong province, got her first injection in Hong Kong in May, but when she returned for her second in July she was told it had been postponed until mid-October. "Many people are waiting to get vaccinated," she said. "It's impossible to get fully vaccinated within the time frame suggested by the pharmaceutical companies."

She has been told she will not be able to receive her third and final shot until March, about 10 months after her first injection.

Although HPV vaccines are available on the mainland, some women prefer to travel to Hong Kong to receive Gardasil-9, a secondgeneration product from Merck Sharp & Dohme that protects against nine strains of HPV, which combined are responsible for an estimated 90 percent of cervical cancer cases. Gardasil-9 is not approved for the mainland market.

Xu booked her appointment via WeChat with MJ Life, a private clinic, and was asked to pay in full after her first shot. However, the clinic released a notice on Oct 10 saying it would be unable to administer any more Gardasil-9 shots until Dec 1.

Patients were advised to either delay their bookings, fly to Kuala Lumpur in Malaysia at extra expense to get the shot or switch to Gardasil, the first-generation product that protects against only two major HPV strains.

According to media reports, the shortage of Gardasil-9 was caused by a cyberattack on the pharmaceutical company that affected production. The company has not responded to those reports.

Kun Ka-yan, a doctor specializing in obstetrics, said delaying the second or third shots for more than a month could lower the effectiveness of the vaccine. However, he added, no HPV vaccine offers 100 percent protection against cancer, so women should ensure they receive regular cervical screenings.

According to the Hong Kong Hospital Authority, cervical cancer was the city's eighth-deadliest cancer in 2015, causing 169 deaths.