IN EARLY 2020, with the coronavirus pandemic tearing across the world, most people thought it unlikely that a vaccine would arrive any time soon. And as work to develop vaccines began, there were dire warnings of the difficulties ahead. That is why it is so remarkable that, heading into 2021, it seems likely that one or more working vaccines will soon be available. That this can be said with such certainty reflects the number and diversity of approaches being taken.

Scientists have developed many different ways of making vaccines. The oldest method is to take the virus, in this case SARS-CoV-2, and hobble it in some way so it does not cause disease when it is given. This can be done by weakening it, or even killing it entirely. Codagenix, a biotech startup, is making a “live-attenuated” vaccine of this kind. The virus is alive, but its ability to replicate has been restricted. TwoChinese efforts—one from Sinovac and another from Sinopharm—are using inactivated versions of SARS-CoV-2.

In recent times genetic engineering has greatly increased the range of possible vaccines. A popular technique is to take a different, harmless virus and use it as a sort of transport system to deliver a key portion of the SARS-CoV-2 virus. This “sheep in wolf’s clothing” approach is being used by one of the leading vaccines, being made by AstraZeneca, a drugs giant. Based on a chimpanzee adenovirus, it infects cells and delivers instructions to make the SARS-CoV-2 spike protein, thus priming the immune system to recognise the real virus.

Most exciting of all are the nucleic-acid vaccines, where a gene that codes for a bit of the virus is injected directly into the body. That bit of the virus is then manufactured inside the body from the instructions provided, again priming the immune system. Two leading vaccine-makers, Pfizer and Moderna, are pursuing this novel approach, with promising results. It would allow easier manufacturing at scale than other kinds of vaccine.

Stanley Plotkin of the University of Pennsylvania, inventor of the rubella vaccine, says that what he has seen so far of covid-19 vaccines suggests that those which generate responses to the spike protein will be able to protect people exposed to the virus from developing covid-19, at least in the short term. What remains less clear, though, is whether these vaccines will be able to prevent people from carrying the virus and spreading it to others.

Emergency authorisation of vaccines is likely in late 2020 but supply will be extremely restricted. In the first quarter of 2021, vaccine-makers will have more data that will allow regulators to widen the use of these novel vaccines. Demand will still vastly outstrip supply—a problem that will continue throughout 2021.

The coming year will see difficult political and public debates about how to prioritise the use of this supply. Although there are fears about vaccine nationalism, one of the surprising features of 2021 will be how many countries work out how to work together well to produce and distribute these. The COVAX initiative, to which more than 180 countries have signed up, hopes to avoid the ugly and self-defeating situation in 2020 that saw countries trying to outbid each other for limited supplies of PPE and ventilators. The scheme allows rich countries to subsidise vaccines for poorer countries, with the initial aim of vaccinating 3% of the population in all member countries, starting with front-line health workers. The hope is that coverage can be expanded to 20% by the end of the year, focusing on those at highest risk.

A few countries that look likely to be oversupplied with vaccines, such as America and Britain, will try to vaccinate as many people as possible before the winter of 2021. That will raise ethical questions, as most countries will have to be more strategic. The pandemic could be brought under control without vaccinating everyone. UNESCO, the main UN agency organising the global distribution of vaccines, says universal vaccination will not happen in the “initial years” of the outbreak.

Nada Sanders, a professor of supply-chain management at Northeastern University, says the availability of a vaccine will not lead immediately to vaccinations, because so much else needs to be organised. There are concerns about the availability of everything from medical glass to needles. She says the supply chain needs to be designed and mapped at a global scale, and worries that this will take longer than expected. Analysts at ubs, a bank, warn that “fill and finish”, where the vaccine is put into vials and packaged for distribution, is one of the most significant bottlenecks, followed by shipping. All these issues will pose problems in 2021.

And there is one final complexity. The first vaccines to arrive will need to be kept cold during distribution. Currently at least 25% of vaccines arrive in a degraded state due to problems with the cold chain.

One thing is clear: vaccines will arrive, but they will be distributed unevenly, within countries and among them, simply because of the scale of the distribution problem. In the coming year, many people will struggle to understand why loved ones have been lost to a disease for which there is a vaccine. In 2020 heroic efforts have produced vaccines in months, rather than years. In 2021 further heroic efforts will be needed to get them from the laboratory to the clinic.

This article appeared in the Science and Technology section of the print edition of The World in 2021 under the headline “A shot in the arm”

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