Vaccines and testing

The current NZ Covid restrictions happened because someone at risk of infection in their job developed symptoms consistent with Covid and got tested.   With the first load of Pfizer vaccines arriving today, that raises a question about testing.

All the current vaccines seem to do best at preventing serious illness and death, and slightly less well at preventing mild illness. We don’t have really good data on preventing asymptomatic illness, but the information we have suggests that the trend continues and they’re somewhat less effective at preventing asymptomatic illness.  For most purposes that’s a great tradeoff — Covid is a global catastrophe only because people get sick and die, that’s how it’s different from the common colds caused by other coronaviruses.  For preventing border incursions things are more complicated.

When we vaccinate the first target group — people working at the border, the highest-risk healthcare workers, and their household contacts — we dramatically reduce the chance they will get sick or die from Covid, and we reduce, less dramatically, the chance they will get infected and pass the virus on.  We should expect fewer cases of the virus getting past the regular workplace testing — but when it does, it’s less likely to be stopped by someone stepping up and getting a test on their own.  Outbreaks are likely to be bigger by the time we see them, with a higher risk of needing lockdowns.

This doesn’t mean we shouldn’t vaccinate border workers. The whole point of the vaccine is to stop people getting sick and dying, and that’s how we should use it. The answer isn’t to use MIQ workers as coal-mine canaries. We do need to think about how to change testing to respond to the new circumstances.  Many experts have already been calling for more frequent testing of high-risk workers, ideally using new saliva-based tests to reduce the ouch factor.  The case for more-frequent tests will be much stronger as we progressively vaccinate the people at highest risk and become less likely to pick up outbreaks by waiting for people to get sick.