This study is actually a good one, but many of the more dire interpretations being floated around in the media are definitely overblown and misleading. There is actually a lot of good news in this study, but the media chose not to focus on the positive findings. That would give people too much hope, and hey, we can’t have too much hope floating around allowing everyone to see the situation as it *really* is. (insert eye-roll emoji here if you feel so inclined)
I read the full paper that was published in the Lancet (linked below). In the first phase of this study, they sampled the blood of about 60,000 people in Spain from April 27th to May 11th and measured for the presence of antibodies. They looked for two different antibodies: one specific to the Spike (S) protein, and the one specific to the nucleocapsid protein of the virus.
The good news is that 90% of people who had a positive PCR test at least 2 weeks before their blood was drawn had antibodies in their blood. This means that the large majority of people who have been exposed to the coronavirus are mounting an immune response that involves the adaptive IgM/IgG pathway, and the antibodies are recognizing different parts of the virus. This agrees with separate studies which have drawn the same conclusion. This is good news, and it’s curious that the media articles that covered this research didn’t discuss this very encouraging result. It’s also important to note that the antibody response via memory B cells is only ONE way our immune system develops adaptive immunity to foreign invaders like viruses (more on that in a later post).
Another conclusion from the study is that the average percentage of the Spanish population that possessed antibodies was approximately 5%. What is *not* mentioned (hmm, that’s curious) in the news articles that covered this study is the fact that there was a significant range associated with this average depending on the location. In certain high population centers, the % of people who had antibodies approached >3 times this, or 17%. Many of the higher density provinces were between 12%-17% (shown in the figure below). But most of the headlines focused on the 5% number averaged across the country. Also remember that this seroprevalence data was gathered at the end of April, and it’s been almost 3 months since then.
Based on this seroprevalence data, most of the headlines read something like, “Herd Immunity Can’t Be Achieved.” Really?
If you look at the daily new cases curve, and daily deaths curve, they hit their peak on March 30th-April 1st. (See figure below). This was approximately four weeks before the seroprevalence samples were taken for this study between April 27th – May 11. Remember, on this date, the average number of infected individuals across the country was 5%, with many high-density regions in the 12-17% range. However, this is not an accurate representation of the number of people who were infected on that date, because it takes 2-3 weeks to develop antibodies. Therefore, this Spanish study is really measuring the percentage of the population that was infected 2-3 weeks before this, which is about 1 week after the peak at the end of March occurred.
Herd Immunity is defined as when the rate of new infections begins to decline due to a sufficient percentage of the population possessing immunity to the virus, thereby reducing the probability of a susceptible individual encountering an infected individual. So, looking at this data, it’s quite conceivable that Spain may have already reached herd immunity (on a global scale, not a micro-regional scale) sometime around this peak. It’s important to note that herd immunity does not mean that no new people will become infected. More people continue to become infected after herd immunity is reached, but the rate of new infections drops after herd immunity is reached. This means that the virus cannot exponentially expand through the average population like it did in the initial naïve population, and lockdown orders have increasingly smaller impact on the overall outcome.
Also, remember that herd immunity is a regional phenomenon, meaning that some pockets within Spain may have already reached herd immunity while certain geographical pockets may not. Based on the seroprevalence data, I would anticipate that this is the case. This means that you may see some bumps in the daily case rates as lockdown orders are continually relaxed.
However, to say that this study proved that “Herd Immunity Can Not Be Reached” is ludicrous. This study combined with the case rate and death data in Spain actually shows that it’s very probable that herd immunity will be reached naturally, and that it’s not going to be anywhere near 70-80% of the population to get there.
Someone might argue that this peak is not due to the herd immunity threshold being obtained, but due to the fact that Spain exercised strict lockdown measures.
To take a look at that theory, let’s look at the relaxation of the lockdown orders. Phase Zero of re-opening started on May 4th. Phase One started on May 11th for many regions and provinces. Phase Two started on May 25th. Phase Three started on Monday June 8th (over a month ago) for many regions – with 70% of Spain now in Phase Three which started on June 15th (4 weeks ago).
Now, look at the daily new cases starting on May 4th when Phase 0 began. The new cases were precipitously declining then, and continued to so until a relatively stable flat line formed from June 7th – July 7th. Daily deaths have been on a steady decline since March 31st, with a relatively stable flat-line minimum since the beginning of June.
Now, as Spain continues to relax towards normal, some micro-regional pockets within Spain may start to see increased cases. In fact, you see a little peak starting to form now. But, it’s important to know that they are now including antibody tests in new daily case data, meaning that these could be double counting of people who were already infected, or people who were not picked up on a PCR test earlier, but now have been added to the pool due to antibodies being developed at a later point in time.
Remember, Herd Immunity is really a regional phenomenon, and just looking at the average can be misleading. However, with up to 17% of people in the denser regions testing positive for antibodies to SARS-CoV-2, the mainstream media would claim that they are far from reaching herd immunity.
In a previous post I go through the mathematical models that predict that the Herd Immunity Threshold (HIT) for SARS-CoV-2 is somewhere in the 10-20% range, not the 70-80% that is being reported in the media. Remember, this radical change in the herd immunity is due to population heterogeneity. Please read that article again if you need a refresher.
Based on these mathematical models, and the fact that many of the more densely populated provinces in Spain were in the 12-17% prevalence range, it’s quite probable that some of these provinces have already reached the HIT. And this data corroborates the mathematical models that predict a much lower HIT for SARS-CoV-2.
So, while most of the media spun this report from Spain to sound negative, I’m looking at the data and seeing many positive signs. First, 90% of people are developing antibodies. Second, it’s very probably that Spain is very close to HIT, at least in certain regions of the country. Third, this validates other epidemiological mathematical models which predict that the HIT for SARS-CoV-2 is in the 10-20% range. If this holds true in the U.S. on a regional basis, this is much better news than what we are being fed.
I’ll cover the topic on “antibodies disappearing” in a separate post. Again, this is a false representation because media professionals do not understand how the immune system works.
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Pollán, Marina, et al. “Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study.” The Lancet (2020).