Is COVID vaccine protection fading?

August 25, 2021

This article has not been updated recently

The UK’s COVID vaccine rollout has been a triumph, with nearly 42 million people receiving both doses in less than eight months. However, some research studies are now suggesting that the protection provided by the vaccines may start to wear off over time, especially against the now-dominant Delta variant.

Our latest analysis of data from the ZOE COVID Study supports this observation, showing that the protection provided by two doses of either the Pfizer or AstraZeneca vaccine wanes over a number of months.

Here’s what we found.

Protection provided by COVID vaccines fades over time

This work builds on our previous analysis of vaccine effectiveness and after effects following the initial vaccine rollout, which we published back in April in the journal Lancet Infectious Diseases

This time, we analysed data recorded by ZOE COVID Study app contributors who logged their COVID vaccinations between December 8, 2020 and July 31, 2021. We then looked to see whether any of these people reported a positive COVID test result between May 26 this year, when the Delta variant became dominant in the UK, and the end of July.

This analysis included:

  • 411,642 test results from users who were doubly vaccinated with the Pfizer mRNA vaccine at the time of the infection 
  • 709,486 test results from users who were doubly vaccinated with the AstraZeneca vaccine
  • 76,051 test results from users who were not yet vaccinated at the time of the infection

We found that initial protection against infection a month after the second dose of the Pfizer vaccine was 88%, while after five to six months this fell to 74%. 

For the AstraZeneca vaccine, there was around 77% protection a month after the second dose, falling to 67% after four to five months.

These graphs show the reduction in the risk of infection since May 2021 for the AstraZeneca and Pfizer vaccines, from two weeks to a month after vaccination (top bars) down to 5-6 months (bottom bars). The shorter the bar, the lower the protection.

Bar graph showing infection risk reduction decreasing over time in COVID vaccines

It’s important to note that these figures have been adjusted to give an average risk of infection reduction across the population. But because we are all unique and our immune systems may respond in different ways to the vaccine, there will be variation in individual levels of immunity and infection risk.

What do these findings mean?

With more than 1.2 million test results and participants, this is one of the largest real-life vaccine effectiveness studies on record. 

It’s only possible through the work of all our contributors who logged their jabs and test results in the app - thank you!

The data from the ZOE COVID Study provides vital information about how COVID vaccines are performing ‘in the wild’, outside the controlled confines of clinical trials.

The six month safety and effectiveness trial of the Pfizer vaccine, which were carried out when the original Alpha variant was dominant, showed that the jab provided a 96.2% reduction in infection risk up to 2 months after the second dose, with an 83.7% reduction after more than 4 months. 

Our findings show that in the real world there is a slightly lower level of protection to start with, as well as a more pronounced wane over time. 

This could be for many reasons, including a greater number of people with underlying health conditions in the general population compared to trial participants and variability in how the vaccines were stored and administered.

This means that the majority of people who had their second dose five to six months ago will be older or vulnerable due to other health reasons, placing them at increased risk of COVID-19 compared to those vaccinated more recently.

Should we be concerned about waning protection from COVID vaccines?

Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to get fully vaccinated.

Importantly, not only does your vaccine help to protect you, it also protects those around you who aren’t yet vaccinated. This includes children and people with weakened immune systems who don’t respond as well to the vaccine. 

The discovery that vaccine-induced immunity against COVID-19 fades over time is not unexpected, although it might require a new vaccination strategy over the coming months.

Professor Tim Spector, lead scientist at the ZOE COVID Study, says:
“A reasonable worst-case scenario could see protection below 50 percent for the elderly and healthcare workers by winter. With high levels of infection in the UK, driven by loosened social restrictions and a highly transmissible variant, this scenario could mean increased hospitalisations and deaths. 

“We urgently need to make plans for vaccine boosters, and based on vaccine resources, decide if a strategy to vaccinate children is sensible if our aim is to reduce deaths and hospital admissions.” 

You can hear more from Tim and other experts discussing these findings and the potential need for vaccine boosters in our latest expert webinar. 

You can help with vital COVID vaccine research

We still need to gather more data to know for sure how vaccine effectiveness changes over time in different age groups, particularly in younger people and those who have had two doses of the AstraZeneca jab. 

To do this, we need as many people as possible of all ages to download the ZOE COVID Study app, log your vaccines and do a daily health report. It only takes a minute, but you’ll be contributing to life-saving research. 

Stay safe and keep logging.

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