WHEN the first trial results for covid-19 vaccines were announced back in November, it seemed that the end of the coronavirus pandemic was in sight. But then came news of first one dangerous new virus variant and then another. So where does that leave us? Will new variants scupper efforts to get life back to normal?
No one can say for sure what will happen next, of course. But many researchers are optimistic that in countries that get hold of enough vaccine, life could mostly return to normal in around a year or less. And in the long run, rather than us facing a never-ending battle with increasingly dangerous new variants, the expectation is still for covid-19 to turn into a mild disease.
鈥淚f it becomes endemic and mild in the way our studies predict, it really wouldn鈥檛 be any worse than the common cold,鈥� says Jennie Lavine at Emory University in Atlanta, Georgia. 鈥淚鈥檓 not saying we know that鈥檚 going to happen but even with what鈥檚 going on now that鈥檚 not an unreasonable prediction for the longer-term future.鈥�
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Key questions
What happens over the next few months depends on the answers to two questions, says .
Firstly, even if vaccines or a previous infection don鈥檛 prevent infection with a new variant, will they prevent severe disease? And secondly, can a country vaccinate a large enough proportion of its population?
鈥淚f the answer to both these questions is yes, then I think a much more normal life is possible in [around six months鈥� time],鈥� says Kilpatrick.
Most countries aren鈥檛 going to get hold of enough vaccine any time soon, says Kilpatrick. 鈥淪o 鈥榥ormal鈥� life won鈥檛 be possible except through infection, which would likely be terrible for many countries.鈥�
For countries where vaccination is happening, there is encouraging news from Israel, which by early February had given at least one dose of the Pfizer/BioNTech vaccine to 90 per cent of people aged over 60. Even before then, by mid-January, the number of people hospitalised with covid-19 had begun to decline, with suggesting that this is an effect of vaccines.
Unfortunately, even vaccinating most of a population doesn鈥檛 necessarily guarantee an end to the pandemic. 鈥淎 significant outbreak with many hospital admissions is still possible after the completion of the vaccination programme, if controls are lifted too quickly,鈥� says Matt Keeling at the University of Warwick, UK.
The problem is that not everybody will get vaccinated and even some of those who do may not be protected against severe disease. That means many could still be vulnerable.
The issue then becomes preventing the virus reaching these vulnerable people. If enough people have enough immunity 鈥� the herd immunity threshold 鈥� the virus cannot spread.
鈥淚n countries that can get hold of enough vaccine, life could mostly get back to normal in a year or less鈥�
The new variants make this harder to achieve. The B.1.1.7 variant first detected in the UK is around 50 per cent more transmissible, for instance, which might raise the herd immunity threshold from 67 per cent of the overall population to 80 or 90 per cent.
鈥淭he emergence of more transmissible variants makes achieving herd immunity very unlikely with the AstraZeneca vaccine, although it should still be achievable with high-efficacy vaccines like the Pfizer, Moderna and Novavax products,鈥� says Zo毛 Hyde at the University of Western Australia.
Even though the Oxford/AstraZeneca vaccine has a lower efficacy than these other vaccines, , so countries battling outbreaks should roll it out as soon as possible, says Hyde.
For countries that have pretty much eliminated the virus, such as Australia and New Zealand, one downside is that few people have natural immunity. By contrast, as many as a third of people in the UK may have been infected, so reaching the herd immunity threshold via vaccination will be easier.
Then we have B.1.351, the variant first detected in South Africa, and the P.1 variant first seen in Brazil, both of which can, to some extent, evade antibodies created in response to previous infections and vaccination. This means people infected with these variants are more likely to pass them on, which again makes reaching the herd immunity threshold harder.
The big worry with B.1.351 and P.1 is that they might evade these antibodies to such an extent that they cause severe covid-19. We still don鈥檛 know how seriously ill someone would get if they were reinfected with one of these variants, says Lavine. 鈥淚鈥檓 still hopeful, but I think this is a really important question to answer.鈥�
There is reason to be optimistic. Trials of a vaccine from Johnson & Johnson show that while it was less effective at preventing mild or moderate disease in people infected with P.1 or B.1.351 than with past variants, it was just as effective at preventing severe disease, with no hospitalisations or deaths in anyone given the vaccine.
This may be due to how immunity works in the body. Antibodies are crucial for preventing infection in the first place. They work by binding to and blocking the part of the coronavirus spike protein that helps it get into cells. B.1.351 and P.1 have several mutations, including one called E484K, that change the shape of this part, which will help it to evade those antibodies and could cause mild or moderate illness.
Once people are infected, however, T-cells, which form part of another branch of the immune system, help mop up infected cells, preventing severe disease. Crucially, T-cells are effective as long as they can recognise any part of the spike protein. This means it is much harder for the coronavirus to evolve to evade T-cells.
The Pfizer/BioNTech vaccine to B.1.351, suggesting that it will remain effective at preventing severe disease even if it is less effective at preventing infections.
Another reason for optimism is that there is a limit to how much the virus can evolve and still function, says Lavine. For instance, the virus won鈥檛 be able to enter human cells if the part of the spike protein that binds to them changes too much.
What鈥檚 more, one study looking at which mutations could help the virus evade antibodies found that made the biggest difference. So it may be that we have already seen the single worst mutation.
If so, we might not need to tweak vaccines more than once or twice, although of course we cannot be sure of this. There is still a chance that something unpredictable could happen, such as the virus, known as SARS-CoV-2, recombining with another coronavirus to produce a more dangerous strain.
鈥�67%
Herd immunity threshold with previous variants鈥�
鈥�80-90%
Probable herd immunity threshold with B.1.1.7, the current dominant variant in the UK鈥�
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Cautious optimism
What we do know is that the four human coronaviruses that have long circulated in people cause only mild illnesses. This is because pretty much everyone is exposed to them in childhood, and they don鈥檛 cause severe illness in children.
Since SARS-CoV-2 is also very unlikely to make children seriously ill, Lavine鈥檚 work suggests that it will end up doing the same.
It might be undergoing a period of rapid evolution as it adapts to a new host that is starting to become immune, says Lavine, but things should settle down in the longer run. 鈥淭he prediction of it being mild in the long term doesn鈥檛 change because of the variants, it just pushes out the time frame.鈥�
Others are more cautious. 鈥淐ertainly, I think we can hope this can be the case,鈥� says Emma Hodcroft at the University of Basel in Switzerland. 鈥淏ut even if this does become an endemic, relatively harmless virus, how long will that take? I think we should prepare for optimistic and slightly less-so scenarios.鈥�
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