The emergency-use authorisation followed quickly after a panel of external advisers to the US Food and Drug Administration (FDA) voted unanimously, with one abstention, to recommend use of the vaccine on 17 December. One week earlier, the agency authorised a similar vaccine made by Pfizer of New York City and BioNTech of Mainz, Germany, about a week after UK regulatory authorities did the same, a report in Nature said.

The speed of these authorisations reflects the urgency of the pandemic, and is a testament to the scientific advances that made rapid vaccine development possible, said immunologist James Hildreth, president of Meharry Medical College in Nashville, Tennessee, at the panel meeting on Thursday. “To go from having a sequence of a virus in January to having two vaccines available in December is a remarkable achievement.”

The authorisation is a first for Moderna, a ten-year-old biotechnology company that had long pledged to revolutionize medicine by harnessing RNA as a therapeutic agent, but had yet to push a drug or vaccine all the way through to the clinic. It will join a growing list of organizations with coronavirus vaccines that are being deployed around the world, including teams in China and Russia.

In the United States, the vaccines offer a glimmer of hope amid the prospect of a tough winter. The country is logging thousands of deaths from COVID-19 each day, and this is expected to rise over the winter holiday season. Coronavirus infections are so rampant that Moderna was able to reach the primary endpoint of its trial five months earlier than expected, said Jacqueline Miller, senior vice-president and head of infectious diseases at the company.

RNA vaccine
Moderna’s vaccine, which was developed in collaboration with the US National Institute of Allergy and Infectious Diseases, works in the same way as the one produced by Pfizer and BioNTech. Both consist of RNA molecules encased in lipid nanoparticles. The RNA in both vaccines encodes a slightly modified form of the SARS-CoV-2 protein known as spike, which enables the virus to infect human cells.

Once taken up by cells, the RNA is used to produce the protein, which then triggers an immune response. The RNA does not enter the nucleus where the cell’s genome resides, and is degraded by the cell within a day of the injection.

COVID vaccine excitement builds as Moderna reports third positive result
Like Pfizer’s vaccine, Moderna’s seems to be highly effective — about 94% — at preventing symptomatic SARS-CoV-2 infections. Its safety profile is also similar to Pfizer’s, with fatigue, headaches and pain at the site of injection among the most often cited side effects.

Since the Pfizer vaccine was rolled out in the United Kingdom and the United States, there have been occasional reports of recipients experiencing severe allergic reactions called anaphylaxis after being injected. There have been no signs of such reactions so far in the Moderna trial, which excluded people who have had anaphylactic reactions to previous vaccines, but not those with other allergies, such as reactions to food.

The two vaccines differ in the composition of the lipid nanoparticle that encases the RNA, and Moderna’s formulation allows the vaccine to be stored at higher temperature than Pfizer’s, which must be kept at −70 °C, much colder than a normal freezer. Moderna’s vaccine can be stored in a −20 °C freezer for 6 months, and in a refrigerator (at about 4 °C) for 30 days. This promises to streamline the logistics of deploying the vaccine, particularly in rural areas and in countries with limited health-care infrastructure.

FDA advisers spent much of the 17 December committee meeting discussing when and how to offer a vaccine to participants in the placebo arm of Moderna’s trial after an emergency-use authorization is granted. Once a coronavirus vaccine becomes available, participants might choose to leave the trial to guarantee that they can get a jab. Maintaining the integrity of clinical trials after vaccine authorization — to collect data on long-term safety and the duration of protection — is a looming challenge for developers.

Last week, Pfizer proposed that when its participants become eligible to receive a vaccine as part of a national roll-out, study investigators will tell them whether they received the vaccine or a placebo. Moderna has instead proposed to ‘unblind’ its whole trial at once after it receives an emergency-use authorization, telling all of its participants which treatment they have received, and offering to vaccinate those in the placebo arm using doses that had already been set aside for the clinical trial.

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Winter is fast approaching in the Northern Hemisphere, and researchers warn that COVID-19 outbreaks are likely to get worse, especially in regions that don’t have the virus’s spread under control, according to a report in Nature.

“This virus is going to have a heyday,” David Relman, a microbiologist at Stanford University in California, was quoted as saying. “We are looking at some pretty sobering and difficult months ahead.”

Infections caused by many respiratory viruses, including influenza and some coronaviruses, swell in winter and drop in summer. Researchers say it’s too early in the COVID-19 pandemic to say whether SARS-CoV-2 will become a seasonal virus. But growing evidence suggests that a small seasonal effect will probably contribute to bigger outbreaks in winter, on the basis of what is known about how the virus spreads and how people behave in colder months, the world’s leading multidisciplinary science journal said.

People will be interacting more often indoors in places with poor ventilation, which will increase the risk of transmission, according to Mauricio Santillana, a mathematician at Harvard Medical School in Boston, Massachusetts, who models disease spread.

But even if there is a small seasonal effect, the main driver of increased spread will be the vast number of people who are still susceptible to infection, says Rachel Baker, an epidemiologist at Princeton University in New Jersey. That means people in places that are going into summer shouldn’t be complacent either, say researchers.

“By far the biggest factor that will affect the size of an outbreak will be control measures such as social distancing and mask wearing,” says Baker.

Seasonal trends in viral infection are driven by multiple factors, including people’s behaviour and the properties of the virus — some don’t like hot, humid conditions.

Laboratory experiments reveal that SARS-CoV-2 favours cold, dry conditions, particularly out of direct sunlight. For instance, artificial ultraviolet radiation can inactivate SARS-CoV-2 particles on surfaces and in aerosols, especially in temperatures of around 40 °C. Infectious virus also degrades faster on surfaces in warmer and more humid environments3. In winter, people tend to heat their houses to around 20 °C, and the air is dry and not well ventilated, says Dylan Morris, a mathematical biologist at Princeton. “Indoor conditions in the winter are pretty favourable to viral stability.”

To assess whether infections with a particular virus rise and fall with the seasons, researchers typically study its spread in a specific location, multiple times a year, over many years. But without the benefit of time, they have tried to study the seasonal contribution to SARS-CoV-2 transmission by looking at infection rates in various places worldwide.

A study published on October 13 looked at the growth in SARS-CoV-2 infections in the first four months of the pandemic, before most countries introduced controls. It found that infections rose fastest in places with less UV light, and predicted that, without any interventions, cases would dip in summer and peak in winter. In winter, “the risk goes up, but you can still dramatically reduce your risk by good personal behaviour”, says Cory Merow, an ecologist at the University of Connecticut in Storrs, and a co-author of the study. “The weather is a small drop in the pan.”
But Francois Cohen, an environmental economist at the University of Barcelona in Spain, says that testing was also quite limited early in the pandemic, and continues to be unreliable, so it is impossible to determine the effect of weather on the spread of the virus so far.

Baker has tried to tease apart the effect of climate on the seasonal pattern of cases during the course of a pandemic, using data about the humidity sensitivity of another coronavirus. She and her colleagues modelled the rise and fall in infection rates over several years for New York City with and without a climate effect, and with different levels of control measures. They found that a small climate effect can result in substantial outbreaks when the seasons change if control measures are only just managing to contain the virus. “That could be a location where climate might nudge you over,” Baker says. The team posted its results on the preprint server medRxiv on September 10; the authors suggest that stricter control measures might be needed during winter to reduce the risk of outbreaks.

If SARS-CoV-2 can survive better in cold conditions, it’s still difficult to disentangle that contribution from the effect of people’s behaviour, says Kathleen O’Reilly, a mathematical epidemiologist at the London School of Hygiene and Tropical Medicine. “Flu has been around for hundreds of years and the specific mechanism as to why you have peaks of flu in the winter is still poorly understood,” says O’Reilly.

And even if researchers had more reliable data for SARS-CoV-2, they would see only small or negligible seasonal effects so early in the pandemic, when much of the population is still susceptible, says Relman.

Over time, however, seasonal effects could play a more important part in driving infection trends, as more people build up immunity to the virus. This could take up to five years through natural infection, or less if people are vaccinated, says Baker.

But whether a seasonal pattern emerges at all, and what it will look like, will depend on many factors that are yet to be understood, including how long immunity lasts, how long recovery takes and how likely it is that people can be re-infected, says Colin Carlson, a biologist who studies emerging diseases at Georgetown University in Washington DC, the report in Nature concluded.

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