Coronavirus latest: Two risk factors for catching Covid post-vaccination – study finding


Whilst approved vaccines have demonstrated their effectiveness in clinical trials and global data, they are not a 100 percent shield when coming into contact with COVID-19. According to, Adeel A. Butt, professor of medicine at Weill Medical College, real-world studies confirm that the Pfizer-BioNTech and Moderna vaccines are 95 percent effective in preventing infection after two doses.

The study, published in MedRxiv, identifies risk factors associated with COVID-19 infection at least 14 days after first vaccination and outlines characteristics of post-vaccination disease.

The King’s College London team looked at adults from the UK who had reported post-vaccination coronavirus infection between 8th December 2020 and 1st May 2021 via the COVID Symptom Study app.

By assessing the demographics of age, frailty, lifestyle factors and geographical locations with infection, the researchers revealed that “post-vaccination infection risk was substantially higher in older adults with frailty and in individuals living in most deprived areas.”

Risk was found to be lower in individuals with a healthy diet and without obesity.

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Professor Penny Ward, visiting professor in pharmaceutical medicine at King’s College London, said of the research: “This report is one of the first to provide information on breakthrough cases of COVID detected post vaccination drawn from the 4.5million respondents that provide daily data using the COVID Symptom Study app.”

Ward alluded to the fact that the app is a self reporting tool, meaning that the data provided was not always daily, with a relative excess of female participants, so it is not completely representative of the UK.

On this, Ward said this does “not detract from the usefulness of the information provided, and we know from past experience that information provided by this group can be very helpful in providing early insight into public health policies.”

“In this case, the information provided is helpful in understanding the potential need for booster vaccinations in a proportion of the frail elderly as we approach winter,” Ward explained.

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Other findings in the study concluded:

  • Vaccination was associated with reduced odds of hospitalisation and high acute-symptom burden.
  • In the 60+ age group, risk of more then 28 days illness was lower following vaccination.
  • Most symptoms were reported less in positive-vaccinated vs. positive-unvaccinated individuals, except sneezing, which was more common post-vaccination.

The research team found that their discoveries call attention to the reduced symptom burden and duration in people infected in post-vaccination.

Whilst the research is reassuring, the team said that the paper’s data should also prompt efforts to boost vaccine effectiveness in at-risk populations.

Furthermore, the team also suggested that targeting infection control measures will still be an appropriate way to minimise COVID-19 infections.

Persistent symptoms lasting more than 28 days were not much affected in cases occurring after a single dose of vaccine, but the incidence was in fact halved (from 11.4 to 5.2 percent) among the double vaccinated.

According to War, this suggests “for the first time that vaccination can protect against Long Covid both by preventing infection and then ameliorating illness experienced following breakthrough infection.”

Regrettably the study did not contain information on illness associated with different variants, and the duration of the study (Dec 2020 to early July 2021) covered the alpha and early delta variant waves in the UK, Ward explained.

Long Covid is assessed in the study by analysing the proportion of cases with symptoms persisting for more than 28 days.

However Long Covid is still poorly understood and the persistence of symptoms post infection, and their severity, remains to be explored.

However, Ward insists that it is “encouraging that the overall proportion of cases with persistent symptoms is reduced in patients that were previously fully vaccinated, which taken together with the milder overall illness and reduction in need for hospital care demonstrates the additional worth of vaccination in reducing severity of illness for individuals and reducing the burden on the NHS by lowering the number of people needing hospital care.”

While the study is unable to draw robust conclusions such as “fully vaccinated people are almost twice as likely to have no symptoms than unvaccinated if they catch COVID-19” as the app is not completely representative of the UK, one can gain insightful results as to who is most at risk of COVID-19 post-vaccination.



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