The number of reported cases depends on how many people actually test when they feel unwell. The true number of infections is likely to be significantly higher. But there is no reason to think testing has dropped off significantly in the past two weeks, or even in the past few months.
The levelling off and subsequent decline of cases fits with the wave naturally reaching a peak. The amount of virus being听听has also decreased in the past week. Altogether this means the fall in cases is likely to be real.
Importantly, cases have been falling in all age groups, including over-70s. This is particularly good news because the听听had been a key driver of the steep rise in hospitalisations and deaths in this wave.
We may yet see an increase in cases in families with school-age children as they returned to school this week after the winter holiday break. But this is unlikely to be enough to reverse the falling trend, and hopefully won鈥檛 affect older age groups to the same extent.
Hospitalisations typically lag behind cases by a week or two. Consistent with this pattern, the number of people in hospital with COVID has recently shown听. It will probably start to fall in the coming week.
Immunity from the first Omicron wave
The BA.5 variant is driving the current wave. BA.5 has taken over from BA.2 as the听, as it has in听.
The leading hypothesis for why BA.5 has been able to outcompete BA.2 is its increased ability to evade immunity 鈥 whether that was acquired through vaccination or previous infection with a different variant.
However, new evidence from听听补苍诲听听(both yet to be peer-reviewed) suggests people who鈥檝e had a previous Omicron infection have relatively strong immunity against BA.5. Qatar and Denmark both have听听and this is evidence of the strength of hybrid immunity.
In England, it is estimated people who haven鈥檛 had COVID previously听听of new cases, despite being听听of the population.
The strength of hybrid immunity induced by high vaccination rates and the large and relatively recent BA.2 wave in Aotearoa likely means this BA.5 wave is smaller than it would have been otherwise.
How long could it go on?
Following the first Omicron wave in March, cases dropped relatively slowly and plateaued at case numbers between 5,000 and 8,000 for several months. It鈥檚 possible we will again see a relatively slow decline in cases.
But there are also grounds for optimism that hospitalisations and deaths could drop lower than they did between the BA.2 and BA.5 waves. Although immunity isn鈥檛 perfect and wanes over time, those who haven鈥檛 yet been infected with Omicron are the easiest targets for the virus. But they鈥檙e getting harder to find as the number of people in New Zealand who haven鈥檛 yet been infected dwindles.
罢丑别听听for eligible people more than six months after their last dose, coupled with building evidence for the strength of hybrid immunity, suggest New Zealand鈥檚 population is increasingly well protected against currently circulating variants.
Tracking reinfections and future waves
Currently, New Zealand is reporting around 500 potential reinfections per day, making up about听. Reinfections will certainly grow over time as immunity wanes.
The true number of reinfections is almost certainly a lot higher because cases can鈥檛 be classified as reinfections if the first infection wasn鈥檛 reported. And it鈥檚 possible people who know they鈥檝e had COVID before are less likely to test, especially since their symptoms are likely to be听听the second time around.
But the fact reinfections are still a small proportion of cases is consistent with evidence that prior Omicron infection provides strong, albeit imperfect, protection against getting reinfected with BA.5.
Continuing to rely solely on people getting tested to keep track of where the virus is spreading will lead to greater and greater uncertainty, particularly if access to free testing becomes restricted in the future.
础听听of a representative sample of the population would be a much more reliable indicator of the true prevalence of the virus in the community.
Another new variant is likely to trigger the next wave. It鈥檚 impossible to predict its timing or exact characteristics with any certainty. The Ministry of Health plans to听听to determine the true community prevalence of the virus.
Having a prevalence survey in place before the next variant takes over would enable us to estimate the size and severity of the next wave more accurately. Combined with听听补苍诲听, this would give us a world-class COVID surveillance system that could provide a blueprint for managing other existing or newly emergent pathogens.
This article was originally published on听.
