Skip to content
#Open journalism No news is bad news

Your contributions will help us continue to deliver the stories that are important to you

Support The Journal
Image: Shutterstock/LookerStudio

FactFind: What are Covid-19 vaccines effective at preventing?

A social media post has drawn incorrect conclusions to suggest that Covid-19 vaccines are ineffective.
Feb 24th 2021, 8:00 PM 19,630 0

A VIRAL SCREENSHOT on social media about the efficacy of Covid-19 vaccines is using misinformation and flawed logic to suggest that the vaccines are ineffective.

The screenshot says that the vaccine doesn’t give lasting immunity and doesn’t prevent someone from getting the virus or from spreading it to others – but whether the vaccines achieve these is something scientists are still investigating as part of the normal research process, not something they have found the vaccines cannot do.

It misrepresents the need for restrictions to continue while people are being vaccinated to mean that the vaccine is not effective, and asks: “What is it actually 95% effective at doing?”

The screenshot was posted to multiple social media pages in January, including on an Irish Facebook page where it has been seen 15,000 times since the start of the year.

Vaccine claims Source: Facebook

The three vaccines against Covid-19 that have been approved for use in Ireland are Pfizer/BioNTech, Moderna, and Oxford/AstraZeneca.

The European Medicines Agency (EMA), which is responsible for recommending to the European Commission whether or not a vaccine should be authorised, considers efficacy to be “the measurement of a medicine’s desired effect under ideal conditions, such as in a clinical trial”.

For vaccines, this means the efficacy rate is based on the risk a vaccinated person is at of getting the disease that the vaccine targets compared to someone who is unvaccinated.

As such, a 95% efficacy rate means that people who have received the vaccine have a 95% lower risk compared to those who haven’t.

Among a population where 1% would have contracted a disease without a vaccine, a vaccine with 95% efficacy would mean that only 0.05% – twenty times fewer – would get the disease. Instead of 1,000 cases in a population of 100,000, there would be 50.

In a clinical trial of the Pfizer vaccine with 44,000 people, half received the vaccine and half were given a control injection with no vaccine, which neither knowing which they had received.

Of those who received the vaccine, eight people later reported symptoms of Covid-19. Among people who did not receive the vaccine, there were 162 cases of Covid-19 symptoms – twenty times more.

For the Moderna vaccine, a trial of 28,000 people gave the vaccine to half the participants and a control injection to the other half.

11 of the people vaccinated with the Moderna jab experienced Covid-19 symptoms, and 185 of those received the control.

The trial found the Moderna vaccine had a 94.1% efficacy overall, and 90.9% efficacy in people at risk of severe Covid-19, such as people with chronic lung disease, heart disease, obesity, liver disease, diabetes or HIV infection.

Similarly, in an AstraZeneca trial, cases were lower among the group that were given the vaccine compared to those who didn’t – 64 cases of symptoms in those who received the vaccine and 154 in those who didn’t, giving it an efficacy of 59.5%.

The World Health Organisation (WHO) has outlined the protection the vaccines give and why restrictions are still needed while people are being vaccinated.

In January, the Director of the WHO’s Department of Immunisation, Vaccines and Biologicals Dr Katherine O’Brien said that the “vaccines that we have right now are all two-dose vaccines”.

“After the first dose, we see a good immune response that kicks in within two weeks of the first dose, and it’s the second dose that then boosts that immune response and we see immunity get even stronger after that second dose,” Dr O’Brien said.

Source: World Health Organization (WHO)/YouTube

“We don’t know yet how long immunity lasts from the vaccines we have at hand. We’re following people who have received vaccines to find out whether or not their immune response is durable over time and the length of time for which they’re protected against disease,” she said.

“The clinical trials demonstrated that these vaccines protect people against disease. What we don’t know yet is whether or not the vaccines also protect people against just getting infected with the SARS-CoV-2 virus, and whether or not it protects against transmitting to somebody else.”

SARS-CoV-2 is the virus that causes the Covid-19 disease.

What this means is that researchers know the vaccines can prevent Covid-19 disease, but it is not known with certainty yet whether they can prevent a person being infected with SARS-CoV-2 and then passing that virus on.

#Open journalism No news is bad news Support The Journal

Your contributions will help us continue to deliver the stories that are important to you

Support us now

A person who has been vaccinated could come into contact with SARS-CoV-2 and not become sick with Covid-19 because of the vaccine’s protection. However, if the vaccine does not prevent against transmission, that person could pass the virus on to someone else who, if they have not been vaccinated, could then become sick.

The most common symptoms experienced by people with Covid-19 are a fever, a cough, and tiredness. Some other symptoms are aches and pains, a sore throat, diarrhoea, and loss of taste or smell, and serious symptoms include difficulty breathing, chest pain, and loss of speech or movement.

The benefit of the approved vaccines that is known for certain is that they can significantly reduce the risk of a person becoming sick from Covid-19 and experiencing those symptoms.

“We really need to continue precautions while we’re still learning about what the vaccines can do; can they protect against getting infected and transmitting to someone else,” Dr O’Brien said.

“Right now, we’re in a situation where there’s still very broad transmission. In many countries, the transmission is just out of control and so for how long we need to continue these precautions is really going to depend on what communities and countries can do to crush this virus, to crush the transmission, and in that way the vaccines can do their best job at preventing disease.”

The three Covid-19 vaccines available in Ireland – from Pfizer/BioNTech, Moderna, and Oxford/AstraZeneca – have all been put through clinical trials to determine their efficacy.

Their ability to prevent people from getting sick with the Covid-19 disease is their key benefit, and scientists are still researching whether they can prevent the transmission of the SARS-CoV-2 virus that causes Covid-19. 

For the European Union, the European Medicine Agency’s evaluation of the vaccines found that they were safe and effective against Covid-19, and the agency will continue to monitor them as further studies are conducted.

Restrictions are remaining in place as vaccines are rolled out to protect people while transmission is still high.

As a result, we rate the claim that the vaccines are not effective: FALSE.

As per our verdict guide, this means: The claim is inaccurate.’s FactCheck is a signatory to the International Fact-Checking Network’s Code of Principles. You can read it here. For information on how FactCheck works, what the verdicts mean, and how you can take part, check out our Reader’s Guide here. You can read about the team of editors and reporters who work on the factchecks here.

Have you gotten a message on WhatsApp or Facebook or Twitter about coronavirus that you’re not sure about and want us to check it out? Message or mail us and we’ll look into debunking it. WhatsApp: 085 221 4696 or Email:

Send a tip to the author

Lauren Boland


    Back to top