Vaccines reduce the severity, length and viral load of Covid-19 in those who still get infected

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  • A new study assessed how effective mRNA vaccines are in real-life healthcare settings.
  • The study found that the vaccines scored highly in preventing Covid-19 infection.
  • People who still had 'breakthrough' infections had milder symptoms and shorter recovery times compared to unvaccinated people.

A new study found that the mRNA vaccines, i.e. the Pfizer and Moderna vaccines, significantly prevented symptomatic and asymptomatic SARS-CoV-2 (the virus that causes Covid-19) infections in healthcare workers.

The research published in the New England Journal of Medicine sought to find out how effective these vaccines were in high-risk settings like healthcare facilities.

Healthcare workers 

The researchers enrolled almost 4 000 healthcare personnel, first responders, and other essential and frontline workers. The study participants were tested weekly for SARS-CoV-2 from 14 December 2020 to 10 April 2021.

The authors of the study then calculated vaccine effectiveness and Covid-19 infection rates in vaccinated and unvaccinated participants. They took readiness to be vaccinated, study site, occupation, and local viral circulation into consideration.

A total of 3 179 participants had received at least one dose of an authorized mRNA vaccine by 10 April 2021 (84% received both recommended doses). 67% were given the Pfizer vaccine and 33% received the Moderna jab.

Effectively combating Covid-19 infection

The findings of the study show that both mRNA vaccines are effective in preventing symptomatic and asymptomatic SARS-CoV-2 infection. The vaccines were found to be 91% effective with full vaccination and  81% with partial vaccination. 

The study found that there was a small number of breakthrough infections (infection despite having received a vaccine). Healthcare personnel who were partially or fully vaccinated at the time of infection had a 40% lower viral load and a 66% lower risk of viral detection for more than one week than participants who were unvaccinated when infected.

Partially or fully vaccinated participants also had a 58% lower risk of feverish symptoms and a shorter duration of illness, with approximately six fewer days of symptoms and two fewer days spent sick in bed than unvaccinated participants. 

"We are still seeing the same high levels of vaccine effectiveness, so we feel good about that. But more importantly, we've added a number of measures of the severity of infection among individuals who have been vaccinated as a comparison to those who haven't, and we measured how much virus there is and for how long," says study co-author Prof Jeff Burgess.

*For more Covid-19 research, science and news, click here. You can also sign up for our Daily Dose newsletter here.

WATCH | Getting to know: Vaccines – the origins

READ | Covid-19: Will vaccinated people in South Africa need booster shots?

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