Getty Images / WIRED / cdc.gov
A couple of breaths is all it takes to catch Covid-19. It sounds obvious – all viruses have to slip inside our bodies in some way or another – but despite the 129 million (and counting) confirmed cases, there are few examples where we can point to the precise moment that someone crossed the razor-thin line between being infected or not.
In New Zealand, authorities investigating a tiny outbreak in September 2020 traced this moment to a 50-second window of time when one infected person likely breathed infectious particles into a hotel corridor, leading to two people in the room next door contracting Covid-19. Even more proof that, given the right conditions, Sars-CoV-2 only needs a tiny window of opportunity to create an outbreak.
This single transmission poses a dilemma for public health authorities in countries where case rates are falling and lockdown measures are easing. When cases are low enough, should we track the source of each outbreak and do everything we can to stamp out every ember of infection, or do we decide that some transmission is inevitable and accept future deaths and hospitalisations as the price of normality?
New Zealand has emphatically chosen the first approach. The country, with a population of 4.9 million, has recorded just 26 Covid-19 deaths. In the last six months, almost all of the country’s reported cases have been imported by travellers, who must spend 14 days in mandatory quarantine in one of the dozens of converted hotels across New Zealand. A single case outside of these facilities is a huge deal. “If [a coronavirus case] is in the communities, it is national news for a week – one case is that newsworthy,” says Jemma Geoghegan, a virologist at the University of Otago who investigated the September outbreak.
One instance of community transmission in New Zealand is enough to send regions into lockdown. On February 14, 2021, when three cases of community transmission were discovered in Auckland, shops were closed, non-local travel banned and socialising restricted to household bubbles. This is why health authorities go to such lengths to pinpoint the source of every infection. “When there is a community case […] this is the level of detail we have to go into to determine where it came from, because if we can’t link it to the border we have to determine where it came from,” says Geoghegan.
On September 18, 2020, New Zealand health authorities were alerted to a positive case of Covid-19 in a person who had flown to Christchurch from Delhi, completed their 14 day mandatory quarantine (including two negative Covid-19 test results), then flown on to Auckland where they later tested positive for the virus. Working backwards from this person – who investigators called case-patient G – officials identified two other linked cases, D and E, who shared a flight with patient G and likely passed the virus on to them.
But identifying D and E posed another question. How did these two people get infected? Before taking their flight to Auckland, D and E hadn’t left their hotel for the 14 days of their mandatory quarantine, and had tested negative for Covid-19 twice. The only time they left their shared hotel room was to put their rubbish in a communal bin left in the hotel corridor. The person in the hotel room next door to D and E, case-patient C, did have Covid-19 and although the three people had never come into contact, investigators hypothesised that C had left virus particles on the bin lid which were then picked up by D or E. In the national press, the bin quickly became the prime suspect behind the new outbreak.
It wasn’t until much later that the mystery was finally solved. An analysis of CCTV footage from the hotel showed that on the twelfth day of their quarantine, there was a 50-second window where patient C’s door was open while they were tested for Covid-19. Although the two adjacent doors were never open at the same time, researchers think that this was enough time for viral particles emitted by C to blow into the corridor and linger in the air long enough to be breathed in by D or E, who were next in line to be tested.
In response, public health officials in New Zealand have changed how people in mandatory quarantine are tested for Covid-19. Instead of going door-to-door, officials now jump between rooms on different floors to complete their tests. The bins, too, have been changed so people can drop their rubbish without touching the lid.
The rigour with which New Zealand officials tracked down every person in the Auckland cluster demonstrates the country’s dedication to a zero-Covid approach. Since the country has no ongoing community transmission, it can direct all of its attention to intercepting cases at the border. But in England, where as of March 13 there were still around 10,900 new positive cases each day and the government’s plan for easing lockdown continues apace, reaching zero-Covid seems unlikely.
The UK government has set the target of offering all adults a first vaccine dose by the end of July 2021, but even then there will be pockets of people who are still vulnerable to the disease. Although the vaccines we have are extremely effective, they do not protect absolutely everyone against infection or illness, and there are some people who can’t get a vaccine because they are severely immunocompromised. Vaccine uptake is also lower among certain minority ethnic groups and the UK government has still not said when, or if, children will be vaccinated against the virus.
A more realistic approach to completely eliminating Covid-19 might be eliminating it as a public health problem, says Kathleen O’Reilly, an epidemiologist at the London School of Hygiene and Tropical Medicine. “It’s bringing transmission down to sufficiently low levels where it has a pretty minimal impact on the public health system. That’s really low hospitalisations, but you’re accepting that there’s some level of transmission that will happen in the population.” Although very low transmission is still a world away from no transmission at all, it will still mean a big shift in the way that outbreaks are handled. If transmission rates get low enough, it’s likely that outbreaks will be dealt with at a local level – more like the way that local health authorities deal with influenza and norovirus outbreaks.
We’ll also need to get to grips with how vaccines are influencing outbreaks. “First we need to understand the role of these vaccines in controlling transmission,” O’Reilly says. We know vaccines are very effective at stopping serious illness and death from Covid-19, but we know much less about how good they are at stopping infections. Future outbreaks in mostly-vaccinated populations will throw up all kinds of questions: are vaccinated people transmitting the disease? Or are there unvaccinated people we’re overlooking?
There’s also the border problem. New Zealand has among the strictest border measures in the world, but it has only vaccinated 1.2 per cent of its population. That’s partly because it has no transmission, says Geoghegan, pointing out that the country has bought 15 million doses of the Pfizer vaccine – enough to vaccinate its entire population more than twice over. In a country like the UK, that has had much looser border restrictions, there’s the risk that even in a mostly-vaccinated population, importing lots of new cases from other parts of the world will spark new outbreaks. “It becomes more of a challenge when people coming from abroad or going on holiday and then coming back have a higher probability of being infected than the local population,” says O’Reilly.
In the long run, the best way to handle ongoing transmission might just be to make sure that hospitals are well-resourced enough to help anyone who does get a serious case of Covid-19. “If you enhance the healthcare system, they can cope with any variant that comes in.” says Julian Tang, a professor of respiratory sciences at the University of Leicester. More intensive care beds and nursing staff will mean the sickest people get the best care possible, although it won’t help the one in seven people who reportedly have symptoms of long Covid.
For countries where new infections are declining to levels last seen in the summer of 2020 it’s tempting to think that the pandemic is almost over. But with most of the world unvaccinated and the threat of new variants still lingering, it’s possible that the pandemic is just moving into its next – potentially most drawn-out – stage. After more than a year spent fighting against Covid-19, do we now need to find a way to live with it?
Matt Reynolds is WIRED’s science editor. He tweets from @mattsreynolds1
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