Knowing precisely how long COVID-19 immunity will last, however, will take some time since the novel coronavirus has only been around for under a year.
“That said, we know that people who were infected with the first SARS coronavirus, which is the most similar virus to SARS-CoV-2, are still seeing immunity 17 years after infection. If SARS-CoV-2 is anything like the first one, we expect antibodies to last at least two years, and it would be unlikely for anything much shorter,” Bhattacharya said.
In the other two studies, each of which was published last week, subjects with COVID-19 had elevated levels of antibodies, especially in severe cases. They also supported the thought that immunity could be long-lasting.
More than 300 coronavirus patients were tested by Massachusetts General Hospital researchers. Most of the patients were severely ill and hospitalized. For as long as months, their levels of IgG antibodies were elevated. The findings were published in the American Association for the Advancement of Science journal, Science Immunology.
“Knowing how long antibody responses last is essential before we can use antibody testing to track the spread of COVID-19 and identify ‘hot spots’ of the disease,” said pediatric infectious disease specialist Dr. Jason Harris, who worked on the study.
In a Canadian team’s study, also published in Science Immunology, patients' IgG antibodies lasted for as long as 115 days after their symptoms initially developed. Researchers used saliva tests in their study.
“This study confirms that serum and saliva IgG antibodies to SARS-CoV-2 are maintained in the majority of COVID-19 patients for at least 3 months [post-symptom onset],” researchers said in the abstract. “IgG responses in saliva may serve as a surrogate measure of systemic immunity to SARS-CoV-2 based on their correlation with serum IgG responses.”
It’s important to note that despite talk of herd immunity, these reports don’t support the notion that any country could get there soon via natural infection.