King's College London

Researchers from King’s College London, together with partners from The Voluntary Health Services, Chennai, India, studied healthcare workers who received the Covishield vaccine (similar to the AstraZeneca vaccine). They looked at both blood and saliva samples to understand how the body responds to the vaccine over time.

What Did They Find?

• Your mouth matters: COVID-19 usually starts in the nose and mouth, but most vaccine studies only look at blood. This study shows that saliva contains important immune signals that may help fight the virus.

• Previous infection changes your response: People who had already had COVID-19 before getting vaccinated responded differently. Their antibody levels didn’t rise as much after the vaccine, possibly because their bodies were already prepared.

• Breakthrough infections are common: Nearly half of those who hadn’t had COVID-19 before got infected after vaccination. But those who had already been infected were less likely to catch it again.

• Long-lasting protection in the mouth: Certain immune molecules stayed active in saliva for months, even when those in blood dropped. This could help explain why some people stay protected longer.

• Memory cells kick in fast: Even when antibodies faded, the body was able to respond quickly to new exposures—thanks to immune memory.

Why Is This Important?

This research shows that vaccines don’t just work in the bloodstream—they also help build protection in the mouth, which could be key to stopping the virus from spreading. It also suggests that people who’ve had COVID-19 may respond differently to vaccines, which could help guide future booster strategies.

Understanding how our immune system works in different parts of the body can help scientists design better vaccines—not just for COVID-19, but for other viruses too.

Find out more and access the paper here: https://www.mdpi.com/2076-393X/13/9/967