Flu Vaccine Loses Efficiency in a Matter of Weeks


While the US Center for Disease Control guidelines advises the administration of the flu vaccine before October ends, a recently published study notes that vaccine efficacy may start to drop in a few weeks after it was administered, reinforcing the idea that one shot is not enough to protect you during the entire flu season.

The research showed that the chance of contacting flu rises to 16% every 28 days after the vaccination. People that took the vaccine at the end of September would be more vulnerable in the long run.

Several flu seasons were observed between 2010 and 2017. The tests included patients that took the inactive influenza vaccine and they were tested for both flu and respiratory syncytial virus, which were used as a control group.

The aim of the study was to find out if patients had a higher risk of getting sick if they took the vaccine before the flu season started. Almost 45,000 patients tested positive for influenza. Out of them, the persons that took the vaccine in a timeframe of 43 to 69 days before being tested were up to 50% more prone to having a positive result when tested. The numbers reached almost 95% for people that were vaccine 154 before the testing period started.

The decrease in efficacy was linked to influenza A protection, as the particular virus strain caused over 80% of the cases that were observed during the study. No conclusive evidence was found for RSV.

The authors gingerly recommended a change of the vaccination schedule towards the end of November. While the results showed that the vaccine could be more effective if it was administered later, any change must be analyzed before it is imposed.

If people opted to get the vaccine before the season started, it would be more effective in theory. But better ways to improve the way in vaccines work and are evaluated are also needed.


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