Herd Immunity in Sweden Shows No Sign of Success
Ever since the first case of novel coronavirus was confirmed in Sweden, the country adopted a more relaxed approach to prevent and control the spread of the virus. Instead of reenforcing social distancing and adopting strict lockdowns measure, the country is placing emphasis on personal responsibility. Many saw it as an attempt by the country to achieve herd immunity, but authorities denied that achieving herd immunity was their goal.
▲ The country has not enforced strict lockdown measures and most restaurants, bars and stores have remained open.
In April, news were reported that Sweden was on its way to achieve herd immunity, but recent studies have shown that Sweden's percentage of people with antibodies is not far off that of other countries that enforced lockdowns.
Herd immunity is reached when the majority of a given population becomes immune to an infectious disease. This is achieved when people become infected then recover from the disease, or through vaccination.
At this point, the majority of the population are considered to have developed antibodies which are effective in eliminating the virus (assuming those who have contracted the virus retain enough protection and the virus does not mutate into a distinct strain). The disease is less likely to spread to people who aren't immune, because there just aren't enough infectious carriers to reach them.
Vaccination is usually the fastest way towards achieving herd immunity, alas, novel coronavirus has no vaccine yet.
▲ The country has not enforced strict lockdown measures and most restaurants, bars and stores have remained open.
Random seroprevalence testing have not yet been undertaken nationwide, but plans are afoot. Nevertheless, the national public health agency, Folkhälsomyndigheten, and Swedish military sampled 738 Stockholmers and found that 2.5 percent were infected between March 26 and April 3 with SARS-CoV-2, by late April the number grew to 7.3 percent.
This number is close to the mathematical model's estimate of the community spread of the virus. According to the analysis conducted by a leading UK group, 3.1 percent of the Swedish population was estimated to be infected by March 28.
But the numbers contrast with the much higher proportions estimated for Stockholm by Tom Britton, a leading Swedish academic working with Folkhälsomyndigheten, who suggested that up to half of the capital’s population will be infected by the beginning of May – and the rest of the country may follow suit quickly.
▲ A healthcare worker cleans and disinfects an ambulance after dropping a patient at the Intensive Care Unit (ICU) at Danderyd Hospital near Stockholm on May 13.
It is estimated that for a population to achieve herd immunity for Sars-Cov-2, sixty to seventy percent of the population need to be infected and develop antibodies.
There are many factors that may prevent the population to reach this rate of infection, for example despite the fact that Sweden didn’t lock things down to the same extent other countries did, individuals in Sweden do not want to get infected, so they are taking some precautions that slows the spread of the virus.
A country like Spain recorded 5 percent of its population had developed coronavirus antibodies by May 14, following preliminary results of an epidemiological study by the government.
The number is not much lower than that of Sweden suggesting no concrete evidence of natural herd immunity developed for Sars-Cov-2, and recent reports showed that Sweden has one of the highest fatality rates in the world.
▲ Scandinavian countries Covid 19 data | Image Credit: Blue Map
What now?
Dr. Marybeth Sexton, an infectious disease expert, hospital epidemiologist and assistant professor of medicine at Emory University in Atlanta, said that achieving herd immunity is a slow process. In fact, the time it will take to achieve it may be a year or so, and by the time it has been achieved, a vaccine will have already been developed long before that.
"The problem is we still don’t know if having antibodies makes you immune — it probably does based on our prior experiences with coronavirus, but we don’t actually know that for sure. And if you do have immunity, we don’t know how long it lasts. For the other coronaviruses, it’s been estimated anywhere from 40 weeks to two years, but this is not permanent protection.
So even if today, you had 60-70% of your population that was immune, that might not be the case a year from now. Herd immunity might not last if you achieved it through natural infection." She concluded.
Source: Interview with Dr. Marybeth Sexton
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