Policy & Global Development

FAQs on COVID-19 Vaccines

We answer some of the questions you may have regarding vaccine safety and efficacy

COVID-19 Vaccine
Photo: Thirdman / Pexels

Thanks to remarkable scientific progress and previous experience with other coronaviruses, a number of COVID-19 vaccines may soon be approved and rolled out in many countries. On this page we will try to answer the questions you may have regarding these vaccines. The initial list of questions will be gradually expanded.

[Last update: 22 January 2021]






Which are the most advanced vaccines against COVID-19?

The following table shows the vaccines against COVID-19 which are on phase III of clinical trials or have finished it.

What are the differences between the vaccines currently tested?

Among the COVID-19 vaccines currently in development, we can distinguish different types according to the technology they use. On one hand, there are the "classic vaccines" that use whole inactivated virus or viral proteins. On the other hand, there are those using more innovative technologies to introduce a gene sequence with the instructions so our body can produce a given viral protein. This genetic information can be introduced directly into the cell (messenger RNA vaccines) or via a viral vector that infects the cell. The vaccine candidates by Pfizer-BioNTech and Moderna are among these "last generation" vaccines. All of them have been tested in people to prove their safety and efficacy throughout the three phases of clinical trials.

Recording date: 26-27 November 2020. 

How do the new mRNA vaccines work?

What messenger RNA vaccines do is introduce into our cells a gene sequence that codes for protein S, which is a SARS-CoV-2 specific protein. It uses somehow the machinery of our cells to make copies of this protein. Afterwards our immune system recognizes protein S as foreign and responds by generating specific antibodies, therefore, when this coronavirus enters our body, we already have immunity and we will not get sick.

Being so new, are they safe?

Yes. We are, without a doubt, before a most promising and innovative technology in the field of vaccines, but not unknown. Although it has not been approved for vaccines in humans before, it is the result of more than a decade of advances in the biomedical field. Furthermore, its safety has been tested throughout all three phases of clinical trials.

Can they give us disease?

No, because they do not introduce the attenuated virus into the body, but genetic material. Furthermore, this messenger RNA involves the synthesis of a protein of the virus, but not of the entire virus. What can happen is that we have some side effects the day after having been vaccinated, such as pain in the arm, headache or fatigue. This is normal, it is a sign that our immune system is responding.

Do they modify our DNA?

Not at all because messenger RNA does not access the nucleus of our cells, so it cannot be incorporated into our DNA.

Do they have advantages over other vaccines?

Yes, they are easier to design and do not involve the handling of infectious material during development.

Recording date: 26-27 November 2020.


Can we trust vaccines that have been developed so quickly?

Vaccines against COVID-19 have been developed in record time thanks to important technological advances and experience gained with the SARS and MERS coronaviruses. However, this does not imply that the process was not rigorous and that the usual steps were not followed. Clinical trials have three phases: the first one consists precisely in confirming the safety of the drug, a fundamental aspect that is also confirmed in phases II and III of the trial, which involve the participation of thousands of people.

The main unknown that remains to be answered as a result of the speed with which clinical trials have been carried out is for how long will these vaccines protect, since at the time they get on the market, their effectiveness will only have been followed for 6-8 months. If their efficacy is observed to decline over time, it will probably be necessary to re-vaccinate.

Recording date: 26-27 November 2020.

Is it safe to be one of the first people to be vaccinated?

All vaccines approved by the regulatory agencies will be absolutely safe, since they will have previously completed the three phases established in the clinical trials. This means that before vaccination campaigns begin, tens of thousands of people will already have received the vaccine during clinical trials.

Recording date: 26-27 November 2020.

What are the risks of COVID-19 vaccines? Can there be side effects?

There is no such thing as zero risk, and this is true for these new vaccines and with other vaccines that are already in the market.

Many vaccines, including COVID-19 vaccines, may have a series of mild and short-term effects such as pain at the injection site, fatigue or headache. This is normal - it measns the immune response is kicking in.

There can also be serious adverse events. But if a vaccine is approved, it means that it has shown to have a good safety profile, which means that the risk of this type of events is very low.

However, when hundreds of thousands of people start receiving the vaccine, one can expect to see some rare adverse events that had not been observed before, including allergic reactions. It is also true that some vaccines use new technologies with which we have little experience, and it will be important to monitor long-term safety. In fact, Pfizer plans on following-up its trial participants during two years.

Ultimately, it is a matter of evaluating benefits and risks for each vaccine. The benefits of the COVID-19 vaccine, in terms of deaths and cases averted, largely outweigh the risks associated to vaccination.

Updated on 17 December, 2020.

Recording date: 14 December, 2020.

Can I get COVID-19 if I have been vaccinated? Can someone who has received the vaccine die of COVID-19?

Although several of the most advanced vaccines have shown an efficacy above 90%, no vaccine is 100% effective. Therefore, we may expect that some people will fall sick with COVID-19 despite being vaccinated and we cannot rule out the possibility that some may even die. But the great majority of vaccinated people will be protected against the disease, or against severe forms of the disease.

Updated on 17 December, 2020.

Are commercialized vaccines subject to surveillance mechanisms?

Of course. This is what we call phase IV trials. In other words, from the moment vaccines are authorized to be distributed and jump to the market, their safety and effectiveness are continuously assessed. It is a phase as strict as the previous that besides monitoring the current vaccines, it will contribute to improving the development of future vaccines.

Updated on 18 December, 2020.

Recording date: 26-27 November, 2020.


When can I get vaccinated?

The answer to this question varies depending on the country of residence and the group to which one belongs. People who are in high risk groups and those who have a greater exposure to the virus will, as a general rule, receive priority over those who are considered less vulnerable.

Forecasts suggest that people from priority groups will be vaccinated during the first half of 2021, while the rest of the groups will begin to be vaccinated in the second half of the year.

If a vaccine turns out to show greater effectiveness in certain population groups, it is likely that those groups will be vaccinated in priority.

Recording date: 26-27 November, 2020.

How is the COVID-19 vaccination effort going, worldwide? How many vaccine doses have been administered in different countries?

Source: Our World in Data based on public official sources.


How long will vaccine-induced immunity last?

It is still too early to give a rigorous answer to this question. Efficacy data from phase III clinical trials of each of the vaccines is beginning to be released. Later, it will be necessary to do follow-up to evaluate the effectiveness of the different vaccines over time.

Recording date: 26-27 November, 2020.

If I have been vaccinated, can I spread the virus?

It is still early to know if the vaccines that are being developed now only protect against disease or can also protect against infection, that is, prevent us from getting infected and infecting others. We will know this later, when there is enough data to examine whether vaccinated people are capable of transmitting the virus.

Recording date: 26-27 November 2020.

If I have already had the disease, do I need to get the vaccine?

Getting the COVID-19 vaccine is advisable also for the people that have already had the disease, since it is not known exactly how long the acquired immunity against the SARS-CoV-2 virus will last.

However, during the first vaccination campaigns, the number of available vaccines can be very limited and, in case of shortage, it could be decided that people who have had COVID-19 - and therefore have a certain level of immunity - are not a priority.

Recording date: 26-27 November 2020.