Explained: Why has Denmark given up on achieving herd immunity via vaccines?

Denmark's SSI infectious diseases agency has said that it no longer believes it will be possible to achieve herd immunity in the country through vaccination, meaning Covid-19 could continue to circulate for years to come.

Explained: Why has Denmark given up on achieving herd immunity via vaccines?
Tyra Grove Krause, the SSI's acting academic director, believes that achieving herd immunity is no longer realistic. Photo: Mads Claus Rasmussen/Ritzau Scanpix

“It is not realistic to achieve herd immunity, understood as meaning that we will not see any spread of infection at all,'” Tyra Grove Krause, the SSI’s acting academic director, told the Ritzau newswire.  “We will still see infections with Covid-19, but we will not see serious complications to the extent that we have seen in the past, because the vaccine will protect us so well against serious disease.” 

Why is herd immunity now a near-unattainable goal? 

Herd immunity takes place when enough people are immune to infection to an illness that its reproduction number (the number of people each infected person in turn goes on to infects falls below one, without any other anti-infection measures in place. The number of infections will then gradually decline until the disease dies out of its own accord.  

Before the emergence of more infectious variants such as the Alpha and Delta variants, most estimates had placed the threshold for herd immunity at between 60 to 70 percent of the population.

The growing dominance of the Delta variant, which is both more infectious and better able to infect people who are vaccinated, has now pushed that threshold to well over 80 percent, and even to as high as 90 percent.

“If the vaccines were 100 percent effective against the variants that are in play now, and we had a 100 percent vaccination coverage among those who are 12 years and older, then we could talk about achieving actual herd immunity against the delta variant,” Krause told BT. “But unfortunately this is not the reality, we can not achieve that.” 

So does that mean we will see more and more outbreaks of the pandemic? 

Perhaps, although future waves will look very different from what we saw last year and this year. 

Krause said that even if Denmark does, as she expects, see a new wave of infections after people return to work and school at the end of this summer, that should not in itself be cause for alarm. 

“We are going into a period where we will be able to tolerate much higher infection rates than we did previously because those who get infected will not become seriously ill,” she said. “Our threshold for when an infection rate counts as “high” has been shifted upwards.” 

This means that it now actually does make sense to treat Covid-19 in the same way as we treat seasonal flu, and not respond to waves of infection with tight restrictions. 

It will be more reminiscent of the flu than before,” she told Ritzau.


Is herd immunity absolutely impossible? 

Not quite. 

Krause said it was still possible that new, more effective vaccines, and a vaccination program involving children under the age of 12, could lead to genuine herd immunity in Denmark, but she said it was possible that even then, new variants would mean continued infections. 

“We are dealing with a virus which is constantly changing a little bit, so you would expect there to be a variant that will dodge this new vaccine a bit.”  

So does this mean Denmark’s vaccination program has failed? 

Not at all. 

Even though the Delta variant has shown itself able to spread even among largely vaccinated populations, this has not been accompanied with significant numbers of hospitalisations and deaths. 

“The Delta variant also does not seriously threaten our vaccination program, because there is still a high level of protection against disease,” Krause said. “And that is the purpose [of the vaccines]: to prevent serious disease. It is not to eliminate viruses.” 

The big question which will determine whether the Covid-19 crisis is finally over, she told BT, will be how long vaccines remain effective. 

“The essential thing is the effectiveness of the vaccines and how long the effect lasts. These two factors will determine how the pandemic develops. We must keep a close eye on this and study it. It is too early to just let the infection run free because we have not yet reached a high enough number of vaccinated.”

Member comments

  1. American here, I’m curious if it’s true that kids in Denmark didn’t wear masks in school last year?

    If they did was it based on location? Age? I can’t seem to find a clear answer, just curious what it was like in Denmark.

    Are there plans to mask kids this coming school year? (Most in US are advocating mandatory masks for aged 2+ all school day except when eating)

    Appreciate any feedback!

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Recent Covid-19 booster jab offers good protection: Danish agency

The number of new registered cases of Covid-19 in Denmark is currently declining despite the cold weather providing more favourable conditions for the virus.

Recent Covid-19 booster jab offers good protection: Danish agency

A weekly trend report from the national infectious disease control agency, State Serum Institute (SSI) shows that 3,781 people returned positive PCR tests for the coronavirus last week, compared to 4,247 the preceding week.

It should be noted that Denmark does not generally advise Covid-19 tests for those not at risk of severe illness from the virus.

READ ALSO: What is Denmark’s Covid-19 testing strategy for the winter?

Going further back, the number has almost halved, with 9,015 positive PCR tests registered during the week beginning October 10th.

The number of people with Covid-19 newly admitted to hospitals has also fallen, from 275 two weeks ago to 245 last week.

SSI has begun to include vaccine effectiveness as a new parameter in its weekly trend report.

According to the agency, people who have recently received a booster against Covid-19 are better protected against the virus than those who have not received a booster.

“Our analyses of the effect of the booster show that persons who received the fourth dose [second booster, ed.] prior to September 15th are well protected against hospital admission as a result of Covid-19,” SSI senior medical consultant Bolette Søborg said in a statement on the agency’s website.

The latest booster provides “around 75 percent better” protection against hospital admission compared to people who have received three doses,” she said.

READ ALSO: Can you get a Covid-19 booster in Denmark if you are not in a risk group?