Expert Group views on serious adverse events with history of HSI vaccination

28 Jan 2010

Members of the Expert Group on Serious Adverse Events with History of Human Swine Influenza (HSI) vaccination, at its meeting today (January 28), reached consensus views on reported cases of Guillain-Barre Syndrome (GBS) and intrauterine deaths (IUD) with history of HSI vaccination.

On the GBS compatible case reported on January 6, 2010, the expert group noted that to date, the World Health Organization (WHO) has found no evidence suggesting a causal relationship between GBS and HSI vaccination and that the reported number of GBS cases worldwide has been in line with usual background rates prior to the introduction of such vaccines.

It was also noted that recent incidences of GBS after the start of HSI vaccination programme in Hong Kong does not increase over the baseline, which is about 40 to 60 cases per year.

"While it is always difficult to completely rule out a rare, idiosyncratic response to any vaccine or drug for an individual patient, literature review shows that the majority of GBS cases that are temporally associated with vaccination occurred from the second to third week, with a median latency of 13 days," a spokesman said.

On the two reported cases of intrauterine deaths with history of human swine influenza vaccination, it was noted that the Department of Health received the reports on January 20 and January 23, 2010 respectively. Both cases had known risk factors, namely, advanced maternal age and long-term medication in one case and gestational diabetes mellitus in the other.

About 150 to 220 cases of IUD occur in Hong Kong every year. A significant proportion, 15 to 70 per cent, of the cases do not have identifiable causes.

It was noted that as at January 27, 2010, a total of 1,375 pregnant women have received HSI vaccine. "Currently, the proportion of IUD among vaccinated women have not exceeded the local baseline incidence of IUD, i.e., around 0.15 per cent versus 0.2 to 0.4 per cent," the spokesman said.

"The rate of stillbirths among vaccinated pregnant women is therefore at the low end of usual background levels."

More extensive overseas experience and recommendations from the World Health Organization (WHO) on the use of human swine influenza (HSI) vaccine in pregnant women have confirmed the safety profile of HSI vaccine including the lack of any demonstrable association with IUD.

"There is currently no evidence that HSI vaccines increase the chance of IUD based on both local data and international experience," the spokesman said.

"It is unlikely that the two observed IUD cases were caused by previous HSI vaccination."