25 Feb 2010
The Expert Group on Serious Adverse Events With History of Human Swine Influenza (HSI) Vaccination today (February 25) discussed four cases reported to the Centre for Health Protection recently.
The first case was one of intrauterine death (IUD) affecting a 28-year-old pregnant woman at 39 weeks of gestation. The expert group noted that the patient received HSI vaccine on December 21, 2009, more than seven weeks before the diagnosis of IUD, at a Maternal and Child Health Centre.
Pathological examinations on the placenta and fetus have been done, pending final results.
The expert group noted that about 150 to 220 cases of IUD occur in Hong Kong every year. A significant proportion (15 to 70 per cent) of them does not have identifiable causes.
As of February 22, 2010, a total of 1,423 pregnant women have received HSI vaccine. So far, the proportion of IUD among vaccinated women has not exceeded the local baseline incidence of IUD which is about 0.2 to 0.4 per cent of total deliveries (including live births and stillbirths). Monitoring of hospital records of IUD from the Hospital Authority (HA) showed that incidence of IUD is within the background level in Hong Kong.
"Extensive overseas experience and the World Health Organization (WHO) have confirmed the lack of any demonstrable association of HSI vaccination with IUD. There is currently no evidence that HSI vaccines increase the chance of IUD based on both local data and international experience," a spokesman for the expert group said.
"It is unlikely that this IUD case was caused by HSI vaccination."
In the second case, the patient was a 75-year-old woman who presented with bilateral lower limb weakness on February 8, 2010 and was admitted to Queen Elizabeth Hospital. The clinical picture and laboratory investigations of this patient are compatible with Guillain-Barre Syndrome (GBS). Tracheal aspirate taken on February 17, 2010 grew Haemophilus Influenzae.
The patient received HSI vaccine on 31 December 2009 at a public outpatient clinic, more than five weeks before the onset of symptoms.
"Literature review revealed that the majority of GBS cases that were temporally associated with seasonal influenza vaccination occur between the second and the third week, with a median latency of 13 days," the spokesman said.
"To date, the WHO has found no evidence suggesting a causal relationship between GBS and HSI vaccination and the reported number of GBS cases worldwide has been in line with usual background rates prior to the introduction of such vaccines."
In Hong Kong, about 40 to 60 GBS cases are seen in public hospitals each year as a matter of baseline incidence.
The expert group noted that the incidence of GBS is higher among elderly persons and during the winter season. A statistical analysis was performed using local GBS data to ascertain if there is higher than expected incidence of GBS among vaccinated persons in Hong Kong.
"The observed number of two GBS cases among vaccinated persons so far lies within normal expectation of baseline incidence that would occur in a population of 170,000 (regardless of vaccination history), adjusted for age and seasonal effects," the spokesman said. "In other words, HSI vaccination is not associated with increased incidence of GBS."
The third case involved a 34-year-old man with unremarkable past health who developed headache on February 20, 2010, followed by diplopia on February 21, 2010. He received HSI vaccine on December 21, 2009, more than eight weeks before the onset of symptoms. His condition improved after treatment in hospital and he was discharged on February 24, 2010. He is now being investigated and followed up to ascertain the final diagnosis.
The expert group noted that according to medical literature, the majority of acute disseminated encephalomyelitis (ADEM) cases that were temporally associated (not necessarily causally related) with vaccination occur between five days and six weeks.
The group considered that his illness was unlikely to be caused by HSI vaccination.
The fourth case was an 80-year-old male patient with history of hypertension, ischaemic heart disease, renal impairment and asthma. He presented with sudden onset of limb paralysis and loss of voice on February 5, 2010 and was admitted to hospital on the same day. He received HSI vaccination on December 29, 2009, about six weeks before the onset of symptoms. He is now in critical condition.
The expert group considered that the patient's current clinical features are compatible with ADEM.
"Based on discharge records of HA, preliminary data shows that between some 40 and 70 cases of ADEM, transverse myelitis and encephalomyelitis are recorded every year in Hong Kong.
"To date, the WHO has found no evidence suggesting a causal relationship between these neurological conditions and HSI vaccination," the spokesman said.