Japan’s rollout of COVID-19 vaccines began belatedly in mid-February, months behind the United States and many other countries. Officials blamed a shortage of Pfizer Inc. vaccine from Europe as the main culprit in the delay. But three months later, with shipments stabilized and officials attempting to accelerate vaccinations, Japan remains one of the world’s least protected.

Officials say there is a critical shortage of trained staff to give shots. Despite Prime Minister Yoshihide Suga’s pledge to have all eligible people fully vaccinated by the end of September, some officials say it could take until next year. It will be impossible for Japan to achieve protective “herd immunity” in the two months before the Tokyo Olympics are to begin.

It’s uncertain whether Japan’s already-strained healthcare system can treat extra visitors during the games as it struggles to handle local patients and mass inoculations.

Suga’s government is facing heavy pressure from a public increasingly frustrated by the slow vaccine rollout and repeated declarations of states of emergency. Many now oppose hosting the Olympics.

WHY THE VACCINE DELAY?

The slow start was because Japan requested domestic clinical trials in addition to Pfizer Inc.’s testing in other countries.

Dozens of nations accepted the results of Pfizer’s multinational tests released in November and began vaccinations. The additional testing in Japan took extra months, though the government then took just two months to grant its approval for the vaccine, much faster than the typical one year.

The vaccine made by Moderna Inc. is to be approved later this month after a similar process for use at two large-scale inoculation centers in Tokyo and Osaka. Approval for a third, AstraZeneca, is pending.

WHY DID JAPAN ASK FOR MORE DATA?

People in Japan are often skeptical about foreign-made drugs, especially vaccines, and officials say they needed to thoroughly address safety concerns.

Pfizer’s international tests were conducted from July to November on about 44,000 people in six countries, including about 2,000 Asians. Japan requested tests on 160 Japanese people, triggering criticism that testing such a small number added little but delay.

Japanese health officials have defended the delay as necessary to build confidence in the vaccine. But Suga has recently acknowledged a need to adapt rules to cope with the emergency.

WHY IS VACCINE CONFIDENCE LOW?

Japan’s mistrust of vaccines is decades old, partly because side effects have often been played up.

In the 1990s, the government scrapped mandatory inoculations after a court ruling held it responsible for side effects linked to several vaccines.

More recently, Japan stopped recommending the human papillomavirus, or HPV, vaccine after media reports of alleged side effects, renewing concerns despite its widespread use overseas as protection against cervical cancer.

WHAT IS JAPAN’S VACCINE TIMELINE?

Inoculations started in Japan in mid-February and only about 1 percent of the population has been fully vaccinated. Less than one-third of the 4.8 million prioritized medical workers have received their second shots as of Wednesday.

Vaccinations for 36 million elderly people began in mid-April, and about half a million have received their initial shots. The government aims to finish their second shots by the end of July, at least a month behind the original schedule, but about 15 percent of municipalities say they still need more time, according to a government survey this week. Health experts and some officials say it may take until next spring for the rest of the population to be vaccinated.

DOES JAPAN HAVE ENOUGH VACCINE?

Japan has secured the supply of 344 million doses, enough to cover its entire population, through the end of this year. That includes 194 million doses from Pfizer, 120 million from AstraZeneca and 50 million from Moderna.

Vaccine shipments picked up in May, and health ministry data show that about 7 million doses are currently sitting unused in freezers, despite initial concerns of supply shortages.

Officials say their bigger concern is a shortage of medical staff to administer the shots. Only doctors and nurses are allowed to give them in Japan’s conservative medical culture.

Dentists are willing to help and are authorized but have not been called upon. Getting shots from pharmacists at drug stores as in the U.S. or from volunteers with no medical background other than brief training as in Britain remain unthinkable in Japan.

IS JAPAN DEVELOPING ITS OWN VACCINES?

Several Japanese companies and research organizations are developing possible coronavirus vaccines, including some that are being clinically tested. Shionogi and Co. said recently it hopes to get its vaccine candidate approved by the end of this year.

Takeda Pharmaceutical Co. will distribute the Moderna vaccine and produce the Novavax vaccine in Japan, and JCR Pharmaceuticals Co. will produce the AstraZeneca vaccine under a licensing deal.

Experts say vaccine development is unpopular in Japan because of its risks, the time-consuming process and a lack of government funding.