Japan's health ministry has suspended two widely-used vaccines made by drugs giants Pfizer and Sanofi-Aventis as it investigates whether they are linked to the recent deaths of four infants.
The infants, aged from around six months to under two years old, died over a three-day period this month after receiving the vaccinations or in combination with other drugs, the health ministry said in a statement.
The two drugs -- used to prevent forms of pneumonia and meningitis -- are Prevenar made by New York-based Pfizer and ActHIB, a drug made by the Sanofi Pasteur wing of Paris-headquartered Sanofi-Aventis.
Sanofi's ActHIB is used in over 120 countries, according to the company.
The two vaccines have been administered to an estimated 1.5 million children in Japan, the ministry said.
There have been no reports so far from the doctors who treated the children that establish a causal relationship between the vaccines and their deaths, according to the Ministry of Health, Labor and Welfare.
In Japan the precautionary suspension remain until at least Tuesday pending the results of an investigation by a group of medical experts.
The ministry reported that three infants under the age of two died within three days of receiving the two vaccine shots, with two of the children also receiving DPT shots for diphtheria, whooping cough and tetanus.
A one year-old died a day after being administered Prevenar and a DPT shot, the ministry said, adding that some of the infants had underlying illnesses.
Prevenar and ActHIB became available in Japan around two years ago.
Authorities decided to suspend them after the four deaths occurred between March 2-4, the ministry said.
"Sanofi Pasteur would like to express its sincere condolences to the families affected by these losses", a spokesman told AFP.
"An investigation is underway to which Sanofi Pasteur intends to fully cooperate with health authorities by providing all data available regarding HIB."
In a statement Pfizer said it was fully cooperating with the ministry's suspension and was in the process of gathering information.
"Our company, taking the safety of patients as its top priority, has studied and assessed accumulated information, including that on causal relationships, with regard to the side effects of all products including Prevenar."
The suspension follows the deaths of two infants in southwest France in late February who had been administered Prevenar.
Health authorities on Thursday said the deaths were not linked to the drug.
In 2009, US firm Wyeth, which was later bought by Pfizer, suspended distribution and quarantined a batch of Prevenar in the Netherlands following reports of the deaths of three infants around the time of vaccination.
Dutch authorities and Wyeth in February 2010 determined there was no correlation between the three deaths and the vaccine injections.
In addition to the four cases, Japan's health ministry said another infant also died in November after receiving his second shot of the ActHIB vaccine, a ministry official said.
Explore further: Survey: Knowledge about HPV vaccine effectiveness lacking