Booster longevity: Data reveals how long a third shot protects

A resident gets a vaccine at a health center in Jakarta, Indonesia. The elderly and people at risk of severe disease will be given booster shots in Indonesia.

The images were taken by Dimas Ardian.

A third shot of the vaccine is critical for protecting against the omicron variant and keeping people out of the hospital.

The first estimates for how long a third shot of the Pfizer vaccine will last have been given by researchers in the U.K. The findings are mixed.

The U.K. Health Security Agency reported Friday that protection against severe disease appears to be more robust than protection against infections.

The researchers found that after the third shot of the Pfizer vaccine, the protection against a symptom is pretty good. The booster reduces the risk by 70% two weeks after the shot.

But it falls quickly. The booster reduces the risk of a symptom by 50%.

The U.K. researchers think the protection will fall to 40% after the third shot.

The vaccine's efficacy against infections depends on the level of antibodies we have, which is the first line of defense against the disease, says immunologist Jennifer Gommerman at the University of Toronto.

After a vaccine shot, the level of antibodies increases quickly and then decreases over time. She says that it's normal and expected, but that protection against infections will diminish with time.

The original version of SARS-CoV-2 is different to the omicron version. Our protection takes a hit in terms of how well those antibodies can recognize omicron.

She says that protection against severe disease doesn't depend on antibodies. The vaccine causes other parts of the immune system to fight off infections.

You might be vulnerable to an infection, but not necessarily vulnerable to disease, because of the decline in antibody levels.

The study from the U.K. found that the booster is more effective against severe disease than it is against infections. After a third shot of Pfizer, the researchers found that the protection against hospitalizations starts out above 80% and lasts for four months.

Protection against severe disease decreases to 40% after six months with only two shots of any vaccine.

The results of the Moderna vaccine study are likely to echo the Pfizer numbers given the similarities of the Moderna vaccine and the delta variant.

The findings from the study raises the question of what the future holds for these vaccines, says immunologist Deepta Bhattacharya at the University of Arizona.

I don't think it's a good idea to ask people to get boosters of the same vaccine every few months. He says that people aren't going to do it. After I got the second of the third shots, I felt terrible.

The goal may need to shift from stopping infections to making sure everyone is protected against disease over the long-term.

"Could we get to the point where public health officials recommend a shot once a year?" I think that is likely. We'll have to wait for the data to see if everyone will need that shot to prevent disease. It's possible that yearly shots won't be essential for everyone.

He hopes that the periodic COVID surge will be a bit more predictable so that people can get a booster before the flu season starts so that they don't get sick.