The coronavirus is a lazy disease - it goes for the people with least resistance.
Unfortunately for New Zealand, that's a lot of us as the vast majority are yet to be vaccinated - and that matters hugely.
Wellington's exposure to the contagious Delta variant via a traveller from Sydney, and moving to alert level 2, highlights the danger as the country's vaccination rollout stretches on.
However, New Zealanders still have tools of protection at their disposal - chief among them mask-wearing.
This variant is a particular wake-up call because it has been known to infect people sharing the same immediate airspace as happened with this current Australian cluster.
It is 40 to 60 per cent more transmissible than the Alpha strain, which was about 50 per cent more infectious than the original virus.
Wearing a mask when you go out to shop, keeping your distance, washing your hands, turning on your phone's Bluetooth and remembering to scan with the Covid app, will help keep yourself and others safe. Anyone who suspects they have symptoms should get a test and isolate.
Overseas, the main vaccines are mostly coping with the variants, although both doses are needed of the Pfizer vaccine being used here for high protection against Delta, which a World Health Organisation official described as "faster" and "fitter" than other variants.
Although Delta is causing an increase in UK infections, the vaccines are keeping people out of hospital and preventing deaths. About 50 per cent of adults there are fully vaccinated. Nearly 80 per cent have had at least one dose.
Most of those impacted by Delta there are either unvaccinated or have had only one vaccine shot. Which is the reason for renewed emphasis in Britain on getting second doses to people and vaccinating younger teens.
Even so, deaths associated with Covid keep falling. The Telegraph reports that: "In the most recent week, there were just 66 deaths where Covid was the primary cause, compared to 292 for flu and pneumonia".
Newcastle is a hotspot for Delta but the city's director of public health, Professor Eugene Milne, told The Telegraph "we are seeing early signs that vaccines are successfully breaking the chain between infection and serious illness".
The infected traveller from Sydney had received one dose of the AstraZeneca vaccine, but this offers just 33 per cent protection against Delta symptomatic infection, according to a Public Health England study.
Israel, which has a high level of vaccination, has found Delta clusters around schools. It has found, mostly mild, infections among fully vaccinated individuals including teachers.
This points to New Zealand needing a very high level of vaccination for enough protection, to starve variants of opportunities to spread. Younger people will need vaccination, and occasional mask-wearing will be something we will have to get used to.
Another overseas consideration is booster shots of different vaccines. European Medicines Agency head of vaccine strategy Marco Cavaleri said "mixing and matching" has proven successful and "often ends up in a better immune response".
Here, we are in a position of getting by with traditional protective measures and getting vaccinated when it becomes available.