Covid-19: the effectiveness of the Pfizer vaccine proven against severe forms over at least 6 months

Published on : 10/05/2021 – 08:17

“Extremely effective against severe forms”. Two doses of Pfizer / BioNTech vaccine are effective against the risks of hospitalization linked to Covid-19 and all its variants for at least six months, indicates a study published Tuesday, October 5 in the journal The Lancet, confirming previous estimates.

The study by Pfizer and the U.S. health network Kaiser Permanente analyzed the medical data of 3.4 million people in Southern California between December 4, 2020 and August 8, 2021.

The vaccine, a bulwark against variants

It shows that the effectiveness of the vaccine against the risk of infection decreases over time, from 88% in the month following the injection of the second dose to 47% after six months.

On the other hand, the vaccine remains 90% effective against the risks of hospitalizations linked to Covid-19, including in the event of infection with the Delta variant, for at least six months, she underlines.

These results confirm those of previous estimates from the US Centers for Disease Control and Prevention (CDC) and the Israeli Ministry of Health, The Lancet said in a statement.

“Our study confirms that vaccines are a central tool in controlling the epidemic and remain extremely effective in preventing severe forms and hospitalizations, including against Delta or other variants of concern,” summarized Sara Tartof, lead author of the study, in the Lancet press release.

Loss of efficiency over time

“A specific analysis of the variants clearly shows that the vaccine is effective against all kinds of variants. People infected with Covid-19 who had received two doses of the vaccine were most often affected due to loss of effectiveness of the vaccine over time and not because a particular variant escapes the protection of the vaccine “, also underlined Luis Jodar, vice-president and chief medical officer at Pfizer.

The researchers recognize some biases in their survey: for example, they did not have data on the respect of wearing a mask, social interactions or the profession of the populations studied, which could have an impact on the probability of contracting the Covid. -19.

According to the study’s authors, these results show the importance of scaling up global immunization and analyzing vaccine effectiveness over time to decide which populations should be prioritized for booster doses.

With AFP