Explainer: How well is the COVID-19 vaccine working overseas?

As Australia begins its program some countries have already vaccinated millions in their population.

The early signs are good with numbers trending down in some countries, but infectious diseases experts say it is too soon to tell whether that is a result of the jab, or restrictions on movement.

Experts say Australia can learn from mistakes and avoid issues faced by other nations rushing to distribute doses and control ballooning case numbers.

Almost 70 countries have begun to roll out a COVID-19 vaccine, with the Pfizer and Moderna vaccines primarily being used.

Israel is leading the world, as almost 45 per cent of its population of around nine million have received at least one dose of the vaccine since late December.

In comparison, about 20 per cent of the United Kingdom's population have had at least one shot and almost 12 per cent of the United States.

Early results are positive. According to Israeli healthcare provider, Maccabi Healthcare Services, the effectiveness rate is 93 per cent.

Maccabi reported last week of 523,000 fully vaccinated people, 544 or 0.1 per cent subsequently contracted COVID-19 and 15 of those required hospitalisation. Four of those cases were severe.

Dr Lesley Russell from the University of Sydney said geography and a strong healthcare system were key to Israel's success.

Israel is a small country which doesn't have the barriers of distance faced by the United States and Australia.

Israel also has a universal healthcare system which means every citizen has a digital record and is easily contactable.

This has led Pfizer to sign an agreement with the nation to receive anonymous data on people receiving the vaccine which may be able to help provide a better picture of how well the vaccine is performing.

In larger countries including the United Kingdom, case numbers and deaths have dropped since vaccine distribution began, however Professor Peter Collingnon from the Australian National University Medical School said it was too early to know why.

"There are good signs of decreasing numbers of cases and decreasing deaths, but equally in some countries where they haven't had such a big vaccine rollout, Sweden and other European countries, are also seeing that," he said.

"It's going to be hard unravelling how much of the decrease in deaths and disease is due to restrictions on movement and people, compared to the actual benefit of the vaccine itself.

"That will unfold with time, but we may not have that answer for another month or two or three."

Professor Collingnon said signs across the world were good so far, but the Pfizer vaccine in particular has caused significant logistical issues.

"What we have learned is the Pfizer vaccine seems to be more effective than the AstraZeneca vaccine, and particularly in protecting against mild and moderate disease, although all of them seem to be good," he said.

"So far, it's stopping people dying and getting serious infections, which is good news. And also so far, there really isn't a lot of frequent unexpected side effects."

The Pfizer vaccine requires specialised storage and comes in multi-dose vials. That means the correct number of patients must be ready to receive a dose when a vial is used or doses will be wasted.

Staff must also be correctly trained in how to use special syringes required for the vaccine.

There have been numerous reports from across the world of vaccine doses going to waste after people failed to show up to appointments or delays in the vaccination getting to the destination.

Professor Collingnon said it was too soon to know the difference between each vaccine but it remained clear they were better at preventing serious disease rather than mild disease and although it would decrease transmission, it would not eliminate it.

"That's one of the issues for Australia ... with the current [strategy] of no transmission at all or lockdown, that's going to be with us for some time."

As Australia prepares to start rolling out the AstraZeneca vaccine next week, Professor Collingnon is hopeful authorities can learn from countries which have been forced to rush vaccine delivery in a bid to control transmission.

"We shouldn't rush this, we need to do it purposefully and in an efficient and rapid way, but not take shortcuts because there's a lot of unknowns," he said.

"We are in the fortunate position, where we can learn from others where they have had to rush it ... by doing it slowly and methodically, making sure everybody is trained, seeing what mistakes have been made overseas."

Professor Collingnon said as vaccination is taken up more broadly overseas it would lessen the chances of returned travellers bringing it back to Australia but that risk could not be eliminated.

"We are always going to have the risk of transmission when people come back, even if they're vaccinated, because it doesn't 100 per cent decrease your chance of having the virus," he said.

"People coming back from areas where there is a lot of virus ... a proportion of them are going to carry the virus, even if they may not be sick themselves."

Sanjaya Senanayake from the ANU Medical School said at the current rate it would be six years before the world was fully vaccinated against COVID-19.

Dr Senanayake told the National Press Club last week, as part of an expert panel, it would be imperative to share the vaccine with developing countries to protect against new more "sinister" strains.

"If we continue this global vaccine rollout while in other parts of the world infection continues unchecked, then we will see more sinister strains emerge which might have further impacts on vaccine efficacy," he said.

Professor Collingnon echoed Dr Senanayake, saying Australia was in the privledged position of having no uncontrolled transmission.

He said doses should be sent to countries in the region at higer risk of the virus before the general Australian population is immunised.