The three cases of meningococcal disease that have appeared in northern Hobart in the past two weeks can be described as an outbreak, even though there were no direct links between them, an infectious diseases expert says.

"We can call it an outbreak because it's geographical, not because of physical contact between people," said Professor Robert Booy, head of clinical research at the National Centre for Immunisation Research and Surveillance in Sydney.

Professor Booy said the disease worked through chains of transmission in the community.

"So the infection goes in one person's throat, they cough or kiss someone, it passes to another person, then to another person, then to another," he said.

"And after about five passages, you can get to someone who gets the disease.

"So you cant make a direct linkage between one case and another because there's been all these asymptomatic colonising events in between people who didn't get diseased but were still carrying the germ."

Professor Booy said an example of someone who might develop a severe case of the infection was someone who had had a viral infection that damaged their throat.

"And the bug goes from sitting there quietly to invading the blood stream or causing meningitis," he said.

Vaccine rollout announced

Vaccines covering the A, C, W and Y meningococcal strains will be available free for under-21s in response to the five recent cases of the disease in Tasmania, the Government has confirmed.

The announcement came a day after the ABC reported the fourth case for the year had presented at the Royal Hobart Hospital without the public being made aware.

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The Tasmanian Health Service announced there were in fact two new cases, making it five in less than two weeks.

The outbreak has already claimed the life of 16-year-old Sarah Beltz last week.

Health Minister Michael Ferguson said the rollout would be a "special expansion of our state-funded program", with the aim to "vaccinate every Tasmanian under the age of 21 and over six weeks old".

He said the outbreak was causing a "particular problem in Hobart's northern suburbs" and that the Government would "be prioritising delivery of this program in the northern suburbs for young people".

Mr Ferguson said the State Government would buy 100,000 vaccinations for dispensing over "the next three months" through public clinics, including allowing in-pharmacy vaccinations for children aged over 10.

The Minister used the press conference to address criticisms from the community, the Labor Opposition and health professionals over the handling of the details of the disease cases, saying the Liberal Government "[rejects] the politics surrounding this and accusations that the Government isn't listening".

"Our priority throughout this entire period has been the welfare of Tasmania's health and also sensitive to the needs of a particular family who have been grieving the loss of their dear loved daughter."

In-pharmacy jabs for kids over 10

Mr Ferguson said there had been a "specific issue here around meningococcal disease strain W".

"This includes one person who tragically died and there has been once confirmed case of strain B, a 20-year-old man who has been released from hospital."

He said advice from the Tasmanian director of public health Mark Veitch had been that the current vaccination program needed to be extended, adding "we have a particular problem in the Hobart area, in the Hobart northern suburbs".

"We will be offering in-pharmacy vaccines for children aged over 10," Mr Ferguson announced.

"I want to say thank you for the Tasmanian media for being very helpful in communicating messages. We need to maintain that, we need to encourage people to keep an eye on their children and keep an eye out for key symptoms."

Program not comprehensive enough

Dr Bastian Seidel urged the Government to communicate the news more quickly. ( ABC News )

Dr Seidel welcomed the program but said it was a "stop gap" that is not comprehensive enough.

"It's very clear if we consult with the national immunisation handbook — that's the authoritative guide that applies to all Australians — and it's very clear in there that the vaccinations against all strains are recommended to all Australians from the age of six weeks," he said.

"Our advice does not change — if you want to protect yourself from meningococcal disease you need to have vaccinations for all strains."

The five recent cases include a three-month-old baby boy, a 36-year-old man and a 70-year-old man, who are all in a stable condition in the Royal Hobart Hospital and are believed to have the W strain.