Questions and answers about vaccines against COVID-19

Coronaviruses are a family of viruses that can cause diseases such as the common cold, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). In 2019, a new coronavirus was identified as the cause of a disease originating in China. It is known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The disease it causes is called coronavirus disease 2019 (COVID-19).

According to the World Health Organization (WHO), about 200 vaccines against Covid-19 are being developed worldwide. The United States and the European Union are expected to approve one or more vaccines in December 2020. Meanwhile, Chinese and Russian authorities have already approved vaccines developed by their countries for “emergency use”.

Three are leading candidates for approval by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). These are the vaccines from BioNtech/Pfizer, Oxford University/AstraZeneca and Moderna.

How do these vaccines work?

Moderna and BioNtech/Pfizer are developing matrix RNA (mRNA)-based vaccines. They are a new type of vaccines that instruct our cells to produce so-called. “spike protein”, which is part of the structure of SARS-CoV-2. Our immune system recognizes this protein as foreign to the body, and as a result begins to produce antibodies that protect us from infection if the real virus enters our bodies. RNA vaccine has never before been approved for use in humans, although people have received them in clinical trials for other diseases.

Oxford University/AstraZeneca are developing a vaccine that is a weakened version of the adenovirus that causes colds in chimpanzees. The same adenovirus was used to make the Ebola vaccine. To combat the coronavirus, the virus is designed to infect but not replicate in human cells. When it enters the nucleus of cells, the engineered virus gives instructions to create the aforementioned “spike protein”, which triggers an immune response by stimulating the body to produce antibodies. This prepares the immune system to attack the coronavirus if the person encounters it later.

What efficacy and safety do candidates demonstrate for approval?

The BioNtech/Pfizer vaccine showed 95% effectiveness in preventing disease measured one week after the second dose. Around 43 000 people were vaccinated in two doses, three weeks apart. The final analysis is based on 170 confirmed cases of symptomatic SARS-CoV-2 infection. The company said 162 of those cases were in people receiving placebo, while eight were in the vaccinated group. Ten cases of severe COVID-19 occurred among study participants, with nine in the placebo group and one in the vaccinated group. No serious adverse events were observed among vaccinated study participants. The only side effects were fatigue, which occurred in 3.8% of people after the first or second dose, and headache, which occurred in 2% of people after the second dose. Adults experienced fewer and milder side effects, the company says. On 2 December, the UK became the first country in the world to approve the vaccine for widespread use. The approval is based on data from only 170 infections, and the actual efficacy may be lower than in the trial.

Moderna’s vaccine showed effectiveness in 94.5% of patients, the company says. It is administered in two doses with an interval of four weeks between them. 30,000 people participated in the trials, with half receiving the vaccine and half receiving placebo injections. During the trials, 185 people in the placebo group got sick from Covid-19, and some of them severely. In comparison, there were 11 cases of Covid-19 in the vaccinated group, none severe.

The Oxford University/AstraZeneca vaccine is being tested in two groups in its current trials – in the UK and in Brazil. In the UK trial group, patients were given half a dose at the first vaccination, followed by a full dose 28 days later, resulting in 90% effectiveness. In the Brazilian group, participants were given two full doses 28 days apart and efficacy was 62%. The data also show a strong immune response in the elderly. The press releases did not circulate details of what side effects the study participants experienced. The company reports only that no serious safety events have been confirmed to date and that the vaccine is “well tolerated on both dosing regimens.” The UK study was paused in July and again in September after two volunteers reported neurological problems. Later investigations found no link between the vaccine and those symptoms, and regulators allowed the trial to resume in October. Although we know the number of participants enrolled in each of the trials in the UK and Brazil (2,741 in the UK versus 8,895 in Brazil), we do not know how many received the vaccine (placebo or meningococcal vaccine), which raises the question of how many people were infected with the virus in the UK group that demonstrated 90% efficacy. A factor to bear in mind is that Oxford University/AstraZeneca measure their results differently from their two main competitors. The Moderna and Pfizer/BioNTech studies only caught Covid-19 infections that had progressed enough to cause symptoms, while the AstraZeneca studies conducted weekly tests among participants, allowing them to detect much milder cases – including potentially asymptomatic infections. Trials are still ongoing with over 20 000 volunteers.

How are vaccines stored?

The BioNtech/Pfizer vaccine should be stored at a temperature of approximately -70°C. It will be transported in a special box packed in dry ice and with GPS trackers installed. The vaccine is shipped to countries in special dry ice containers, each containing 5,000 doses. Countries may choose to store vaccines in a “freezer farm” for up to 6 months at -70°C. In unopened dry ice containers, the vaccine has 10 days to reach vaccination centres. Once delivered, the vaccine can be stored for up to 5 days in a refrigerator at 2 to 8°C.

Moderna’s vaccine requires long-term storage at minus 20°C and is stable for 30 days at refrigerator temperatures between 2 and 8°C.

The Oxford University/AstraZeneca vaccine may be one of the easiest vaccines to distribute because it does not need to be stored at very low temperatures. It can be stored in a normal refrigerator, at temperatures between 2 and 8°C, for at least six months. This is why it has become a leading contender in lower-income countries that cannot afford the costly storage chambers of mRNA-based vaccines.

Do vaccines prevent transmission of COVID-19?

No one so far has demonstrated that it prevents infection entirely or reduces the spread of disease in the population. This leaves open the possibility that those who are vaccinated may remain susceptible to asymptomatic infection and transmit this infection to others who remain vulnerable. Pfizer said their scientists are looking at ways to assess disease transmission in future studies. AstraZeneca and Oxford University may be the first to establish whether the vaccine can prevent transmission. Although they have yet to publish the full results, early indications are that the vaccine may have reduced infection rates. This suggests that disease transmission may also be reduced.

How long will immunity last after vaccination?

There is no quick way to determine how long immunity to SARS-CoV-2 will last, and researchers will need to monitor this closely over the coming months and years. There have been some reports of reinfection and declining antibody levels months after initial infection with COVID-19, but it is not yet clear how prevalent reinfection is. There are also signs that the immune system is building up specialised T memory cells that can kick into action quickly if the virus is encountered again. Tracking infections among people who are vaccinated is necessary, with antibody and immune cell levels assessed periodically.

How much will the vaccines cost?

Moderna has received just under $1 billion in funding from the Biomedical Advanced Research and Development Authority (BARDA) and has committed to deliver 100 million doses to the U.S. in a deal worth up to $1.525 billion, making the cost about $50 per patient, or $25 per dose (since each patient requires two doses).

Pfizer and BioNTech have set an initial price of $19.50 per dose, which equates to $39 per patient, in their $1.95 billion contract with the U.S. federal government. This money will pay for the first 100 million doses, pending regulatory approval. Pfizer and BioNTech last month struck a distribution deal with the European Union to supply more than 300 million doses at an undisclosed cost.

In May 2020, BARDA committed up to $1.2 billion to support the Oxford University/AstraZeneca vaccine, aiming to provide 300 million doses to Americans. AstraZeneca, unlike Moderna and Pfizer/BioNTech, has promised to sell its vaccine at around $3 to $4 and not make a profit on the vaccine while the pandemic lasts.

Together, all of the above highlights that there is still much to learn about the new vaccines, although they are all ready to launch immediately. The Moderna, Pfizer/BioNTech and Oxford/AstraZeneca teams have committed to publishing the results of their experiments in peer-reviewed journals. But, distribution under restricted use could begin as early as next month pending regulatory approval.

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