Does the vaccine actually work - what’s the evidence from one of the world’s most vaccinated countries?

By Stuff reporter

The Whole Truth: Covid-19 Vaccination
By Stuff senior writer Nikki Macdonald

In April, a fully vaccinated New Zealand border worker contracted Covid-19, raising questions about the vaccine’s effectiveness.

The Pfizer/BioNTech jab that’s used here has already been widely used in other countries. Israel has vaccinated more than half its population with the vaccine.

The evidence from Israel, then, gives a strong insight into what the Pfizer/BioNTech vaccine can do.

A study in The Lancet medical journal found the two-dose vaccine was 97%  effective at preventing fully vaccinated people from getting symptomatic Covid-19. Two weeks after the second jab, it provided 98% protection against hospitalisation and death.

Those are crucial statistics, as the most important thing is to stop the virus from putting people in hospital or killing them. Remember the flatten-the-curve graph? The priority was reducing the number of people with a serious disease, so hospital intensive care units would not be overwhelmed.

To what extent vaccines prevent people from getting silent infections, without developing Covid-19 symptoms, and how well they prevent vaccinated people from spreading the virus, is less certain.

Designing vaccines to prevent Covid-19 is complicated by the fact the disease has two distinct phases. The first is a more mild but infectious early phase, which affects the nose and throat. In the second phase, which only affects some people, the infection spreads to the lungs, causing breathing problems and organ failure.

So a vaccine aimed at stopping serious disease might not be as effective at preventing that milder but infectious first phase. Preventing serious disease prevents the health crisis of overflowing hospitals. But to kill off the pandemic completely, vaccines need to also prevent more mild infection.

Preventing silent infection

The Israel data looks hopeful. It found that one week after the second dose, the Pfizer/BioNTech jab was 92% effective at preventing silent infection with SARS-CoV-2, the virus that causes Covid-19. That increased to 94% after 14 days.

Even if an immunised person does become infected, such as the managed isolation worker who tested positive for Covid-19 after having one vaccine dose, they are still less likely to pass the virus on.

That’s because there’s some evidence vaccinated people who become infected have a smaller level of virus or viral load. Another study from Israel (not yet peer-reviewed) suggested the average viral load was four times lower after only one dose of the two-jab vaccine. 

One thing that could hinder the ongoing effectiveness of Covid vaccines is the emergence of new, more infectious virus variants. If the virus keeps changing, booster shots or regular update jabs might be needed, such as with the annual flu vaccine.

The Lancet study authors concluded that Israel’s experience showed two doses of the Pfizer BioNTech vaccine were “highly effective” and corresponded to a marked drop in SARS-CoV-2 infections and severe disease.

“These findings suggest that high vaccine uptake can meaningfully stem the pandemic and offers hope for eventual control of the SARS-CoV-2 outbreak.”

Reporting disclosure statement: Immunisation Advisory Centre director Nikki Turner provided expert advice for this post.