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Can vaccines bring herd immunity? It's doubtful

A lot of stock is being placed in COVID-19 vaccines bringing about "herd immunity”.

Some governments and officials hope they could suppress the pandemic altogether.

But the concept comes with caveats, and experts say such expectations are misplaced.

Reuters’ health correspondent Kate Kelland:

"Some scientists are worried that the concept of herd immunity is being misunderstood. They worry that people wrongly believe that it would be something that they can rely on as individuals to protect them even if they don't get vaccinated. And they also think there was a misconception about what's involved in achieving herd immunity."

Estimations of the threshold we'd need to reach for herd immunity varies - depending on who you ask.

Most estimates say between 60 to 70 percent of the population needs to have immunity - either through vaccination, or from previous infection.

But that hinges on the elusive reproduction rate - or “R value".

the measure of how much the virus is being transmitted and how much it is circulating.

"The R value is really important when it comes to trying to figure out what percentage coverage we need to get herd immunity with vaccines. The problem is that we can't calculate the R value of this disease. That's partly because it's a new virus and partly because we are not living in normal times."

Another unknown is whether vaccines will stop the transmission of the virus.

Evidence so far suggests they will at least stop people developing the disease.

But it cannot be ruled out that people will still catch and spread the virus.

"The data we've seen so far from the front line of vaccines from Pfizer, BioNtech and from MODERNA do suggest that they are very good at preventing disease. So there's a 90 to 95 percent efficacy rate in preventing disease [...] this doesn't however mean they will stop transmission of the virus."

So some say aiming for herd immunity is fruitless.

Instead, vaccine deployment should be focused on protecting the vulnerable.

"In terms of herd immunity, the vaccines that we're seeing, the data for now the front runners, aren't going to do the job [...] What some of the experts that I've spoken to are saying is that what we should be focusing on is protecting the most vulnerable people. So vaccinating the most vulnerable people, the old and those with co-morbidities and not trying to chase off to this idea, this elusive idea, of herd immunity."