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Explained: What does Covid-19 vaccine effectiveness mean?

Two vaccine manufacturers are optimistic about their experimental vaccines after the latest studies, but what does Covid-19 vaccine effectiveness mean?

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More than 180 nations have signed up to the pact, which was started with the idea that none of us will be safe until all of us are safe. Source: 1 NEWS

Vaccine effectiveness refers to the likelihood that a coronavirus shot will work in people.

Two vaccine makers have said that preliminary results from their late-stage studies suggest their experimental vaccines are strongly protective. Moderna this week said its vaccine appears nearly 95 per cent effective. This comes on the heels of Pfizer’s announcement that its shot appeared similarly effective.

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The first batch of coronavirus vaccines could be available in New Zealand by early in the new year, Chris Hipkins said. Source: 1 NEWS

Those numbers raised hopes around the world that vaccines could help put an end to the pandemic sometime next year if they continue to show that they prevent disease and are safe.

Effectiveness numbers will change as the vaccine studies continue since the early calculations were based on fewer than 100 Covid-19 cases in each study. But early results provide strong signals that the vaccine could prevent a majority of disease when large groups of people are vaccinated.

Medical syringes seen at Moderna. Source: Getty

US health officials said a coronavirus vaccine would need to be at least 50 per cent effective before they would consider approving it for use. There was concern that coronavirus vaccines might be only as effective as flu vaccines, which have ranged from 20 per cent to 60 per cent effective in recent years.

The broad, early effectiveness figures don’t tell the whole story. Scientists also need to understand how well the vaccine protects people in different age groups and demographic categories.

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A US company’s Covid-19 vaccine which it says is nearly 95 percent effective is “about as good as you can get”, says Professor Graham Le Gros. Source: Breakfast

For both vaccines, the interim results were based on people who had Covid-19 symptoms that prompted a virus test. That means we don’t know yet whether someone who’s vaccinated might still get infected - even if they show no symptoms - and spread the virus.

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New US Covid-19 vaccine almost 95 per cent effective, tests show

Also unknown is whether the shots will give lasting protection, or whether boosters will be required.