There's plenty to show that islands (New Zealand and Iceland showing up in the ) are better at blocking pandemics jvia quarantines and blocking traffic. You can look at the
outcome of 1918 influenza pandemic in that region. The islands with strict naval quarantines got it later and with substantially less severity then the ones who did not have a strict quarantine. By contrast, New Zealand at the time did not have a quarantine or border control measures in place and so was infected immediately and at greater severity. Iceland meanwhile initially failed to impose quarantines but managed to with later quarantines protect a portion of
their population. (Full text is behind paywall, abstract is sufficient). You can look at studies that show that just
reducing the number of travelers into the low hundreds alone would be enough to give a pacific island around a 50% chance of not having a disease outbreak outright, that's without further measures by the way. The idea is valuable enough to justify
studies on the subject (using NZ as the example amusingly). There are other historical examples such as the cholera outbreak in Italy back in 1835-1836 where Sardinia was the only part which evaded the plague by virtue threatening to shoot anyone who attempted to land there. The concept is not a new one.
It even bears out on modern cases,
the countries with low rates are typically either islands, remote African nations or warzones, all of which are factors which make it easier to keep travelers and thereby Corona out. (Well barring China and Vietnam but frankly I'd sooner take the Africans' numbers at face value then those two.)