What’s happened in one of the most vaccinated countries?

In April, a fully vaccinated border worker contracted Covid19, 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 that vaccine can do.

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

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

To what extent vaccines prevent people getting silent infections, without developing Covid-19 symptoms, and how well they prevent vaccinated people 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 affects only 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 crisis of overflowing hospitals. But to kill off the pandemic completely, vaccines need to also prevent more mild infection.

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

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

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 Another study from Israel (not yet peer-reviewed) suggested the average viral load was four times lower after only one dose of the twojab vaccine.

One thing that could hinder the ongoing effectiveness of Covid vaccines is the emergence of 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-CoV2 outbreak.’’

Vaccines need to also prevent more mild infection.