- Four coronavirus immunity studies released in recent days deliver several key conclusions about COVID-19.
- One study says that coronavirus antibodies stay at high levels six months after the initial infection, suggesting COVID-19 immunity might last for at least six months.
- Separate research indicated that reinfection might occur more often than we think. Reinfections are likely to be asymptomatic, but reinfected people may still spread the virus.
- Two different studies found that COVID-19 survivors might develop a strong immune response after a single-dose vaccination, suggesting new vaccination protocols for survivors may be worth considering.
About a year ago, the world began to realize that the novel coronavirus was more dangerous than initially believed, and COVID-19 was spreading across the globe. By late February 2020, it was clear the virus was highly infectious as it started ravaging Italy, Korea, and Spain. Soon after that, the coronavirus pandemic was declared. Fast forward to late January 2021, and the world has access to several vaccines that are already working. Unfortunately, the virus has been evolving as well, and there are a few key genetic changes that make new mutations highly infectious and more resistant to vaccines.
But one year later, we’re finding better answers about COVID-19 immunity that could help craft new public health policies to beat the pandemic. Four new studies indicate that COVID-19 immunity should last for at least six months after the initial infection, that the rate of reinfection might be a lot higher than we think, and that COVID-19 survivors might only need a single-shot vaccination to boost their immunity.
Coronavirus immunity duration
According to Reuters, a major study from the UK delivers great news about COVID-19 immunity. Scientists have concluded that survivors still have high levels of antibodies at least six months after the initial infection. These antibodies are likely to protect them from reinfection.
The UK Biobank measured antibodies in COVID-19 survivors and found that 99% of them had antibodies three months after the infection. After six months, 88% of them still had antibodies.
“Although we cannot be certain how this relates to immunity, the results suggest that people may be protected against subsequent infection for at least six months following natural infection,” UK Biobank chief scientist Naomi Allen said.
One limitation of the study is that it can’t determine the risk of reinfection. It’s also unclear whether any of these patients were reinfected with a coronavirus virus during those six months. Moreover, it’s unclear how mutations might impact antibodies, especially the South African strain. Israel registered one such case of reinfection with the B.1.351 mutant in a 57-year-old man who tested positive after experiencing a runny nose upon returning from abroad. He had no other symptoms, and he did not spread the virus to any other people he came in contact with.
Reuters points out that a separate study from the UK last month found that people who had COVID-19 were likely to be protected for at least five months, but the researchers noted that they were still able to get reinfected, carry the virus, and spread it to others.
COVID-19 reinfection risk was one topic that researchers from the Icahn School of Medicine at Mt. Sinai studied, CBS News reports. The researchers looked for instances of reinfection while following up on a study that looked at coronavirus transmission in a group of Marine Corps recruits. The initial study proved how efficiently the virus can spread even in a highly controlled environment.
“Our findings indicate that reinfection by SARS-CoV-2 in healthy young adults is common,” Mount Sinai’s Dr. Stuart Sealfon said in a statement.
The researchers believe the reinfection rate might be higher than we thought:
Seropositive young adults had about one-fifth the risk of subsequent infection compared with seronegative individuals. Although antibodies inducted by initial infection are largely protective, they do not guarantee effective SARS-CoV-2 neutralization activity or immunity against subsequent infection. These findings may be relevant for optimization of mass vaccination strategies.
The study did show that people who were reinfected had lower antibody titers. Even so, the reinfected had about 10-fold lower viral loads and showed a shorter duration of PCR positivity compared to those who were infected for the first time. The recruits who were reinfected were also more likely to be asymptomatic.
These are all indications that immunity can still prevent severe COVID-19, even if reinfection is more common than we think.
Vaccine efficacy after COVID-19
Icahn School of Medicine also produced a different study on Monday, concluding that one vaccination dose would suffice to boost the existing immunity in recovered COVID-19 patients. “I think one vaccination should be sufficient,” professor Florian Krammer told The New York Times. “This would also spare individuals from unnecessary pain when getting the second dose, and it would free up additional vaccine doses.”
The researchers compared the immune response of 109 people who had received one dose of either the Pfizer/BioNTech or the Moderna vaccine. Of those, 68 had never been infected with COVID-19, while 41 had already survived the illness. They observed a far “more robust” antibody response in the survivor group, with volunteers showing titers 10 to 20 times higher. In some cases, the immune response was even higher than those who had already received the two vaccine doses. The survivor group was also more likely to report side effects.
Separately, researchers from the University of Maryland in Baltimore reached the same conclusions when studying only vaccinated healthcare personnel. They identified a “statistically significant higher” antibody response in those infected with the novel coronavirus before the vaccine. They concluded that a single-dose vaccine might be enough for people who had COVID-19 and a potential delay in vaccination:
Our findings preliminarily suggest the following strategy as more evidence-based: a) a single dose of vaccine for patients already having had laboratory-confirmed Covid-19; and b) patients who have had laboratory-confirmed Covid-19 can be placed lower on the vaccination priority list.
While these are separate studies and can benefit from additional research and review, they indicate that COVID-19 immunity might be long-lasting after infection, which is good news for vaccines.
If reinfection occurs asymptotically more often than we thought in COVID-19 survivors, the same might happen after vaccination. This indicates that survivors and those immunized will have to continue respecting health measures until the pandemic ends.
Finally, if a single-dose vaccine provokes the same response in recovered COVID-19 patients as a two-dose regimen in uninfected people, new protocols might be developed to help accelerate current vaccination programs.