Experts are concerned the Ministry of Health's internal and public health advice isn't aligned with the latest science, Marc Daalder reports
Ministry of Health officials advised the Government to distribute less effective surgical masks to vulnerable communities because they were concerned people might become complacent if given highly effective N95 respirators.
This is one of a handful of recent decisions experts say aren't fully aligned with the latest science on Covid-19. The ministry has been urged to provide clearer advice both on mask use and what a positive RAT result means at the end of a Covid-19 case's isolation period.
Better masks may erode compliance, MoH advised
The advice on masks came in a late April briefing to then-Covid-19 Minister Chris Hipkins and the current Covid-19 Minister Ayesha Verrall. In the briefing, which was released under the Official Information Act, officials provided three types of masks that could be given to "clinically vulnerable and at-risk populations".
Those included the gold standard N95 or P2 respirators, alternative respirators like the Chinese KN95 or Korean KF94 which are almost as good, and typical surgical masks.
Officials conceded that "P2/N95 particulate respirators ... are likely to provide the greatest level of respiratory protection of the three options considered. It is estimated that the fitted filtration efficiency of such a respirator is up to 98 percent, compared with around 38.5 percent for a [surgical mask]."
At a population level, however, the Ministry of Health thought surgical masks were "likely to be more effective than particulate respirators in reducing transmission of Covid-19 (and other respiratory illnesses), serious illness and death".
That's because they were concerned people would not know how to wear a respirator properly and because "a possible perception by some individuals that they are 'protected' by a higher grade of mask may increase complacency and reduce compliance with fundamental infection prevention and control practices: the benefits of increased respiratory protection may be offset by reduced compliance with basic practices, such as staying home when sick, physical distancing or hand washing."
Amanda Kvalsvig, an epidemiologist at the University of Otago and one of the earliest advocates for mask use in New Zealand during the pandemic, said there was no reason to think respirators would be less effective at a population level than surgical masks.
"The two main factors that determine mask effectiveness are filtration efficacy (how good the mask is at filtering out particles, in this case virus) and fit quality (how well the mask fits on the face). Filtration efficacy is well-studied and respirator masks are clearly much more effective virus filters than medical masks," she said.
"For effectiveness at the population level you need to add in one more factor, wide coverage. The more people that are wearing masks, the better the system works because you then have two-way protection: source control (people wearing masks are breathing less virus into the air around them) and respiratory protection (people wearing masks are breathing in lower amounts of virus). You can see that this system works better both ways when people are wearing good-quality masks.
"There’s no basis for recommending that New Zealanders should wear less effective masks in the hope that this would make them more worried about Covid infection and more likely to take other precautions. The evidence definitely does not support this approach."
A study in Nature Scientific Reports from earlier this year said there was no evidence people who wear masks are less likely to follow other health advice.
A spokesperson defended the ministry's view that more effective masks might reduce compliance with other measures.
"This comment was part of a discussion of the real world efficacy of PPE and is a valid concern based on observations of individuals' behaviour. The Ministry of Health undertakes regular behavioural insights surveys to address issues around mask wearing."
This is only the latest time the ministry has been found to be behind the ball on masks. In December 2020, Director-General of Health Ashley Bloomfield told Cabinet mask mandates on public transport should be repealed after summer. A draft paper prepared for Bloomfield in February 2021 similarly recommended a repeal of the requirement to wear masks on public transport.
RAT result debate
Another Official Information Act request has raised further concerns about the evidence base for ministry advice.
As recently as May, official advice said Covid-19 cases who return a positive RAT test after their seven days of isolation are not infectious.
"If you did take a RAT, the result would likely show as positive but that does not mean you are infectious," the Government's Covid-19 website read in May.
When asked in an OIA request to provide the evidence behind these statements, the Ministry of Health responded with a range of links that didn't address the question.
That's because, experts say, the ministry is wrong. RAT results correlate very closely with infectiousness in the latter stages of an infection. And between 12 and 25 percent of Covid-19 cases are still infectious beyond seven days - so a week is a decent rule of thumb but doesn't suit everybody.
"Between 30 and 60 percent of people who are testing positive on a rapid antigen test are still infectious after that seven-day period. And of those who aren't still infectious but did test positive, they were still infectious yesterday," Emily Harvey, the co-lead of the Contagion Network modelling programme at Covid-19 Modelling Aotearoa, told Newsroom.
In other words, even after seven days of isolation, a positive test result could well mean you're still infectious. That's why experts like Harvey have advocated for a test-to-release policy, in which isolation ends once you test negative, in lieu of the seven-day isolation timeframe.
"If you shorten the minimum isolation period but require test-to-release - especially two negatives in a row - you can actually shorten the average isolation period without increasing onward risk," Harvey said.
This could let more people out of isolation sooner, while preventing others from going on to infect people because they were still infectious after seven days.
"The latest evidence on testing methods and strategies for limiting transmission of Covid-19, including the isolation periods, evolves quickly," the ministry spokesperson said, when asked whether any changes to isolation advice were being considered.
"We continue to monitor and evaluate data on a regular basis to inform our approach to testing and isolation. Any changes need to ensure a balance between effective outbreak control, minimising the impact on vulnerable communities and the health system, and the impacts that isolation/quarantine has on wider society."
New advice, communications needed
Even putting aside specific policy changes, both Kvalsvig and Harvey say health communication more closely aligned with the science is crucial.
"I’d like to see the Ministry of Health give a really clear message about how strongly the evidence supports a protective effect of masks. I’d like them to be straightforward with the public about the challenges we face this winter and the important role of wearing masks to dampen the spread of Covid, flu, and many other infections," Kvalsvig said.
"Often, government communications on masks during the pandemic have seemed to suggest that people wanting to wear masks are being over-anxious. That is highly problematic public health messaging for all sorts of reasons. None of us wants to be the one that caused a beloved friend or family member to become seriously ill, and mask wearing can be a key protection for the people around us."
For Harvey, better communication looks like clearer explanations of what a positive test result after seven days means and advice to take extra precautions for a few days even after those seven days are up.
"I think the message hasn't gotten through that these antigen tests are actually detecting live virus. They will only test positive for a day or two after you stop being infectious," she said.
"Some of the earlier messaging about not worrying about positive tests has been removed, but it hasn't been strongly counteracted. The revisions have not been clearly communicated to the wider public."
Ministry webpages currently just advise people not to take a test after their seven days of isolation. But the Ministry of Health spokesperson said the evidence on how to interpret a positive RAT result was still mixed.
"The Ministry of Health acknowledges that a small number of people will remain infectious for more than seven days after they have had a positive RAT result but as time progresses and an individual recovers, a positive RAT is less likely to indicate infectiousness," the spokesperson said.
"The evidence to date on what a RAT result at the end of a seven-day isolation period can tell us about infectiousness is difficult to interpret ... For these reasons, we don’t routinely recommend testing at day seven as it is not a reliable process."
