Tokyo (CNN) -- A safety panel convenes in Japan Tuesday to examine whether two vaccines widely used around the world contributed to the deaths of five children in the past month.
Japan's health ministry ordered doctors to stop immunizing infants with the vaccines while authorities investigate Pfizer's Prevenar vaccine and Sanofi Pasteur's ActHIB vaccine -- commonly given to infants in the United States and other developed nations.
The health ministry said it suspended the vaccines because the children all died within a short period of time; four died last week and one died in February.
Three of the infants had underlying medical conditions, the health ministry said. Authorities are investigating the medical history of one of the children, and the fifth child had no apparent illness at the time of vaccination, according to the ministry.
Both companies maintain that their vaccines -- which are aimed at stopping bacteria that can cause meningitis, pneumonia and other serious infections -- are safe.
"Pfizer thoroughly reviews and continually monitors all of its medicines and vaccines, as safety is our top priority," Pfizer said in a statement. "No causal relationship has been established between the events reported in Japan and vaccination to date. We are conducting a thorough evaluation of these cases in cooperation with the relevant regulatory health authorities."
Sanofi Pasteur said that the company expresses condolences to the families who had lost children, but also said that no causal relationship between the deaths and the ActHIB vaccine had been established.
"We have been and will be providing all data of ActHIB and will fully collaborate with the ministry of health and welfare," the company said.
Prevenar prevents illnesses caused by pneumococcal bacteria and ActHIB prevents infection with the Haemophilius influenza.
Pediatrician Michiko Suwa said Japan's medical community hopes the suspension is temporary and fears the government is overreacting to the deaths.
"I'm concerned that this will impact the future of these critical vaccines," she said, noting that she has been receiving concerned calls from parents since the government announced the suspension.
The World Health Organization has backed the inclusion of Prevenar in national childhood immunization programs, especially in developing nations where infant mortality remains high.
Pfizer estimates it has distributed more than 360 million doses of the vaccine, which is available in more than 100 countries around the world and part of the routine childhood immunization schedule in more than 50 countries. In Japan, 2 million doses have been administered.
The U.S. Food and Drug administration said it was aware of the suspensions in Japan, but "physicians assessing vaccine safety at the FDA and CDC have not detected new safety concerns" related to the vaccines.