Credit ACIP/CDC
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Based on everything we've seen so far, COVID vaccines - and most particularly the mRNA vaccines - provide significant (some would say remarkable) protection against symptomatic, particularly severe, COVID infection.
One of the reasons why the United States, and parts of Europe, are seeing major reductions in cases - even in the face of rising variants - is their relatively high uptake of the COVID vaccine.
But alas, no vaccine is 100% effective across 100% of the population. A very good vaccine - one that provides 90% protection against infection - still leaves 10% vulnerable, albeit usually for milder disease.
When someone is fully vaccinated against a specific disease, and still becomes infected with that disease, it is called a vaccine breakthrough infection (see The CDC's Revamped Vaccine Breakthrough Report).
While we don't know how long vaccine protection will last, or how much of an impact emerging variants will have on the vaccine's efficiency, early data strongly suggests that the vaccines are providing excellent protection in the first few months after receiving them.
Yesterday Denmark's SSI (Staten Serum Institut) released a report on vaccine breakthrough infections in that country since vaccinations began a little over 5 months ago.
One of the advantages of a having s relatively small population (5.8 million), and a universal healthcare system, is their ability to track both who is vaccinated (partially & fully) - and who subsequently contracts the virus - with considerable accuracy.
While they cannot address the duration of protection from the vaccine, or accurately gauge the impact of recently emerged variants, their initial results are promising. Of the (roughly 1 million) people who have been fully vaccinated, only 972 were subsequently confirmed infected (< .01%).
First the (translated) news release from Denmark's SSI, then I'll return with a postscript.
Covid-19 infections after vaccination
The Statens Serum Institut has looked at how many people have been infected with covid-19 after being vaccinated.
Last edited June 7, 2021
On Sunday 27 December 2020, the first Dane was vaccinated against covid-19. Ever since, the roll-out of vaccines has been going on all over the country, and the Statens Serum Institut (SSI) has been closely following the process.
One of the key questions is whether one can get covid-19 after being vaccinated against the disease?
SSI has therefore looked at everyone who has been covid-19 vaccinated in Denmark from 27 December to 1 June.
Infected after 1st vaccination
In the period 27 December to 1 June, there have been a total of 123,179 covid-19 cases in Denmark.
Out of them, there have been 5,801 covid-19 cases among people who have been vaccinated for the first time, but before the person has received another bite. This corresponds to approximately 4.7% of the cases.
Among these 5,891 covid-19 cases, there have been 585 admissions within 14 days of the person receiving a positive PCR test. 312 deaths were recorded within 30 days after the positive PCR test.
Infected after 2nd vaccination
SSI figures also show that 1,334 covid-19 cases were found after a person was vaccinated a second time. This corresponds to almost 1% of the total number of covid-19 cases.
972 out of the 1,334 cases (72.8%) were found after the full effect of the vaccine was introduced. They are therefore called breakthrough infections. That is, infections that "break through" the full effect of the vaccine. The proportion of breakthrough infections corresponds to 0.1% of people with the expected full effect of the vaccines.
Among these 1,334 covid-19 cases, 147 have been hospitalized within 14 days after positive PCR testing, and there have been 40 deaths within 30 days after the positive PCR test. Of those, the 107 admissions and 22 deaths occurred among people with breakthrough infections.
Vaccines are not comparable
SSI has also looked at what covid-19 vaccine people have been given. And whether the number of breakthrough infections is evenly distributed across the various vaccines.
“Since the vaccines have been given to different target groups, it is not possible to compare data for the different vaccines directly. At the same time, there is a difference in when the individual vaccines were rolled out, and thus how large an infection pressure was at the time in question, ”says ward doctor Rebecca Legarth from SSI.
Not certain that death is due to covid-19
According to SSI's figures, the number of hospitalizations and deaths has been fairly stable throughout the period when looking at the people who have received 2nd doses.
"We do not know the details of why the individuals have been hospitalized or died. Therefore, the admissions and deaths cannot with certainty be attributed to covid-19, but since they happened around the time of a positive PCR test, they are classified as covid-related ", says Rebecca Legarth.
Why do people get covid-19 despite vaccination?
SSI points out that even after a long time, small amounts of viruses are excreted, which are captured by the sensitive PCR tests without them having been infected again. And of course, a positive sample can be false positive, but we expect that to be rare.
One possibility is that they have been infected with covid-19 just before they have been vaccinated and therefore only test positive after the vaccination.
"But overall, it is to be expected that a vaccine does not cover 100%, and this may mean that there will be a proportion who get a -often mild- disease course despite vaccination", says Rebecca Legarth.
Breakthrough infections and virus variants
Finally, SSI has looked at whether some of the many covid-19 virus variants increase the chance of becoming infected after being vaccinated.
“Until now, we have only seen a few cases of breakthrough infections for some of the special variants. There is some variation in the incidence of breakthrough infections for different variants, but data are very limited and therefore there is currently no evidence that particular virus variants cause breakthrough infections to a particularly high degree. But this is an area SSI follows closely ", concludes Rebecca Legarth.
See the latest inventory of Covid-19 infection after vaccination .
As good as this data is, no surveillance system is perfect. There may be asymptomatic breakthrough infections not counted, and given how `fresh' these vaccinations are, the duration of protection is still an open question as are the impacts of emerging variants.
But it is hard to argue with the short-term results, which have been impressive.
But as COVID declines (in large part due to vaccine uptake), so does the incentive for those who haven't been vaccinated to get the jab. And that dwindling uptake risks leaving us well short of where we need to be next winter to prevent a resurgence of the disease.
