Are the vaccines working? What after effects are people experiencing? We reveal our first findings

February 9, 2021

This article has not been updated recently

To find out how the vaccines are affecting people, we asked you our ZOE COVID Symptom Study contributors to log their vaccines in the app along with daily health reports.

In our latest expert webinar, Professor Tim Spector, ZOE COVID Symptom Study lead, and Dr Anna Goodman, Infectious Diseases Consultant at Guy's and St Thomas' Hospital in London, share our initial data about how well the vaccines are working, and the after effects that people are experiencing. 

Most people would have a COVID-19 vaccine

A few weeks ago, we added a new question to the ZOE COVID Symptom Study app to find out what proportion of users would be willing to accept a COVID-19 vaccine. 

Nearly 95% of respondents said that they would take a vaccine if offered, but around 5% said they would be unwilling or unsure about accepting a vaccine. 

The top three reasons for being hesitant were concerns about adverse reactions, worries about long-term after effects, and not knowing enough about the vaccine.

“We tend to be very scared of things that are new to us and things that we haven't been exposed to before, but in this context, we have to think about the risk of not having the vaccine and that’s a very real risk,” says Anna.

“People forget just how many people have become very ill with COVID-19 or died of it… You could still catch it next week.”

Our data also showed that people in BAME groups and those living in areas with higher levels of social deprivation were more likely to be hesitant about accepting a vaccine.

“This is an important problem that we need to address because these groups often have two or three times more risk of from COVID compared with the rest of the population,” says Tim, highlighting the need to use alternative routes to reach these groups and reassure them. 

“It is important that everybody gets equal access to the vaccine.”

Read more about our findings on vaccine hesitancy in the app here.

How well are COVID-19 vaccines working so far?

To find out whether vaccination is reducing rates of COVID-19, we compared the rates of COVID positive tests in vaccinated and unvaccinated healthcare workers using the app, many of whom are undergoing regular testing. 

Although the rates of infection are going down in both groups in response to lockdown measures, we saw that rates of COVID-19 were reduced by 50% in vaccinated healthcare workers compared with unvaccinated healthcare workers. 

“It’s fantastic news that we’re seeing this without having to wait for three months to see this result,” says Tim. “I think this data gives us the first impression of the effects of single vaccine doses in real life outside of clinical trials.”

Our results echo those announced by the Oxford/AstraZeneca team, which appear to confirm that one dose of the vaccine gives 76% protection against COVID-19 for 12 weeks

With all this positive news, people are asking how soon after their vaccination they can stop shielding or meet up with others who may be more at risk, such as elderly relatives. 

“Even if you’ve had the vaccine, keep your behaviour the same until we hear otherwise,” says Anna. She stresses that no vaccine gives 100% protection, so people must continue to take precautions to protect themselves and others after being vaccinated while infection rates in the UK remain high.

What effects do people experience after vaccination?

After getting the Pfizer jab, around four in ten people experienced some local after effects, including pain and swelling on the arm where they received the injection. 

Around one in seven also recorded systemic after effects including headache and fatigue, which are in line with the after effects reported in the clinical trial. The reported after effects were short-lived, lasting just a day or two, and we haven’t seen any evidence of longer term health effects.

Interestingly, people recorded more symptoms after the second dose of the vaccine compared with the first. And people who had previously had COVID-19 were also more likely to have after effects following a single jab, compared with those who had never had the disease.

“This is expected,” says Anna. “When your immune system has seen the virus before you tend to have a bit more of a response when you then see the antigen again, which can cause more side effects.”

Click here to read more about the Pfizer vaccine after effects recorded in the app. We don’t yet have separate data about the Oxford/AstraZeneca vaccine.

Help us to monitor the effects of COVID-19 vaccination on health and the progress of the pandemic

We are continuing to collect data about the efficacy and after effects of the vaccines. We’re also digging into the data to understand how the vaccines affect different groups, such as people suffering from Long COVID, and those with underlying health conditions. And we’re watching carefully to see if people who have been vaccinated can still catch emerging new strains of the coronavirus. 

“This is a really exciting area of research that our app is uniquely situated to investigate because we already know so much exactly what's happened to the people who have been logging since the pandemic began back in March,” says Tim.

You can play your part in contributing to vital research about vaccine safety and efficacy by downloading the ZOE COVID Symptom Study app, logging your jab when you get it, and taking just a minute every day to log your health.

Watch the latest expert webinar here:

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