- A comprehensive coronavirus study from Iceland shows that patients who survive a COVID-19 infection are likely to develop antibodies that are detectable in blood tests four months after the initial infection.
- The researchers also proved that as many as 44% of the people who tested positive for antibodies did not have a positive COVID-19 test when they experienced the illness or were placed in isolation. Two-thirds of those people never showed any symptoms.
- This might be one of the most relevant COVID-19 immunity studies so far, considering Iceland’s aggressive testing and contact tracing campaign at the start of the pandemic, which allowed the country to contain the spread of the illness quickly.
The coronavirus immunity topic is quite possibly one of the most important things happening right now. A variety of studies have already detailed various aspects of COVID-19 immunity, and the news hasn’t necessarily been good across the board. We learned that antibodies might disappear three months after the initial infection if they can even be detected to begin with. Recent guidance said that some antibody tests aren’t good enough to meet requirements, and might deliver false negatives. On the other hand, researchers showed that immunity isn’t limited to the antibody response. The immune system remembers the infection with the help of T cells, which can then deal with the same pathogen in case a second infection occurs. Others showed T cells that remember other human coronaviruses that cause common colds could also work against COVID-19. Some of the vaccine candidates that have produced good results induced both the production of neutralizing antibodies and T cells, which is a promising development. Finally, recent reports have shown that a second infection is possible in less than two months, and the second bout of COVID-19 can be as bad or worse than the first one.
This brings us to what may be the most comprehensive coronavirus immunity study so far, which reveals plenty of details about the evolution of the illness inside a community. Among other things, the study says antibodies will typically survive and continue to patrol the body for more than four months after the initial infection.
Iceland may be a tiny nation in the middle of the ocean, but local scientists and health officials gave the world an impressive example of how to contain the infection successfully. As early as early April, scientists from Iceland showed that proper testing and contact tracing campaign can help communities better manage a local COVID-19 epidemic. By knowing exactly how many people were exposed to the virus, how many were infected, and how many needed isolation, Iceland was able to curb the transmission rate and reduce deaths.
Researchers have now published a study in The New England Journal of Medicine that details the COVID-19 immune response in the country. The researchers concluded that antibodies typically last for at least four months after an infection, which is in stark contrast with previous reports that said antibodies might disappear within three months.
The researchers analyzed tests from more than 30,000 people in Iceland, which is over 8% of the country’s population. The group included people with confirmed COVID-19 infections, people who were isolated but never got PCR tests, and people who developed the illness without being detected. Some 56% of the infected persons were diagnosed via regular COVID-19 tests, 14% had been in quarantine (not tested, or tested negative), and 30% were not diagnosed or quarantined.
About 0.9% of the population was infected in the first wave, and the fatality rate was 0.3%. The numbers might differ from country to country, especially in communities where testing is or was inadequate. Iceland seems to be in a position where it has a much better idea of how many people got the illness in the first wave, thanks to that extensive testing program in the first months of the pandemic.
The researchers also noted that most people caught COVID-19 at home from a family member who was infected. “Household exposure was more likely to lead to infection than other types of exposure, which suggests that people who share a household with an infected person should not have contact during quarantine and that contacts of household members should be quarantined,” the study reads. But that’s also where extensive testing helped. “Seroprevalence in the two regional hot spots (Vestfirdir and Vestmannaeyjar) was absent or low outside quarantine, which indicates that most infections were detected by qPCR screening and that quarantine, social distancing, contact tracing, and limits on public gatherings were effective in limiting spread.”
When it comes to antibodies, the study says that over 90% of PCR-positive people remain seropositive 120 days after diagnosis. That’s to say antibody blood tests were able to pick up antibody levels after four months from the initial diagnosis. What’s even better is that “no decrease of antibody levels was detected,” as measured by two of the multi-antibody assays they used. The testers relied on six different tests, including the two assays capable of detecting multiple antibodies. Some single-antibody tests did show reductions in antibodies.
The researchers did address previous studies that said antibodies might disappear after 2-3 months. They noted that the sensitivity and specificity of the tests used might have affected the results. Differences in the patients observed in these studies might also explain the contradicting conclusions. Iceland’s ability to identify more patients than other countries may have played a role as well. “For example, because of widespread qPCR testing and screening, it is likely that the Icelandic qPCR-positive persons were healthy, as compared with the participants in other studies,” the scientists said.
The team also noted that repeated exposure to the virus is “unlikely to affect the persistence of antibody levels in Iceland, given the low prevalence of infection.”
The paper concluded that antibody levels were higher in older people and in people more severely affected by COVID-19. Women had lower antibody levels than men, and smokers also developed lower antibody counts.
Finally, the researchers indicated that coronavirus immunity is yet to be demonstrated in humans, even though studies showed that animals who were survived COVID-19 resisted a second infection. The scientists said that regardless of whether COVID-19 immunity will protect against reinfection or not, the study shows that Iceland remains vulnerable to a second wave because only a small percentage of the population has developed coronavirus antibodies.
