With cases spiking worldwide the question becomes how long will people have immunity to Covid following recovery. There is new data showing somewhat encouraging data. Two new studies show that it seems those with more severe symptoms may have longer immunity. They also show that immunity does diminish over time but may exist for up to 7 months.
The first study was done in the U.K. and was published recently in Nature Microbiology. They looked at 65 individuals who had Covid and an additional 31 healthcare workers who had tested positive. The patients had symptoms ranging from asymptomatic to critical. Antibody studies were done up to 94 days after infection. More than 95% showed antibodies to SARS-CoV-2 but the magnitude of the neutralizing antibody response appeared to depend on disease severity, with lower peak antibody levels in individuals exhibiting milder disease. This kind of antibody response is typical for other viral infections as well. Initially IgA and IgM levels were high but returned to baseline after about 60 days. IgG levels remained high 94 days out. IgA, IgM and IgG are types of antibodies our immune systems produce when there is an infection. IgG are the “long term” antibodies. In patients with mild or asymptomatic disease antibodies were undetectable after 50 days. Their conclusion was as follows: “In some individuals, SARS-CoV-2 infection generates only a transient neutralizing antibody response that rapidly wanes,” the authors suggest. In contrast, antibody levels in patients with high initial levels (ID50 > 4,000) declined but remained in the 1,000 to 3,500 range through the end of the study period.” The link to the study is here: https://www.nature.com/articles/s41564-020-00813-8
Similar findings emerged from a Portuguese study published last week in the European Journal of Immunology. They studied antibody levels in more than 500 hospitalized patients, healthcare workers, and volunteers who had recovered from COVID-19. They found that 90% of SARS-CoV-2–positive individuals had detectable antibodies from 40 days up to 7 months post-infection, with higher levels in patients with more severe disease. They also found detectable IgG antibodies for at least 6 months post infection. Their conclusion was as follows: “Although we observed a reduction in the levels of antibodies over time, the results of our neutralizing assays have shown a robust neutralisation activity for up to the seventh month post-infection in a large proportion of previously virus-positive screened subjects,” explained lead author Marc Veldhoen, PhD, Instituto de Medicina Molecular, Lisbon, Portugal. The article can be found here: https://onlinelibrary.wiley.com/doi/abs/10.1002/eji.202048970
So what happens after 6 months? It IS possible to be re-infected with Covid! In The Lancet Infectious Diseases, Richard L Tillett and colleagues described the first confirmed case of SARS-CoV-2 reinfection in the USA. In summary the 25 year old male patient had two positive tests for SARS-CoV-2, the first on April 18, 2020, and the second on June 5, 2020, separated by two negative tests done during follow-up in May, 2020. Genomic analysis of SARS-CoV-2 showed genetically significant differences between each variant associated with each instance of infection. The second infection was symptomatically more severe than the first. The article can be found here: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30764-7/fulltext
Obviously the first 2 studies are encouraging but the prospect of re-infection is also real. What does this mean for herd immunity? Herd immunity occurs when enough people become immune to a disease to make its spread unlikely. As a result, the entire community is protected, even those who are not themselves immune. Herd immunity is usually achieved through vaccination, but it can also occur through natural infection. Does this new evidence dispel that as a way we can see an end to this pandemic? In some ways yes. It may well be that herd immunity against Covid may ONLY be possible with a safe and effective vaccine. The Covid virus is in the same family of viruses that cause the common cold and we know that you can get that several times in the same year. An excellent article discussing this in greater detail is in Scientific American and can be found here: https://www.scientificamerican.com/article/what-covid-19-reinfection-means-for-vaccines/
I’ll keep you updated on the vaccines as they become more widely distributed and data can be gathered as to it’s effectiveness. In the meantime, remain safe, wear your masks and stay smart!
Your comments and those studies indicate that the bottom line answer is having an effective vaccine, coupled with medicines that reduce the severity of the virus when encountered. Without these it could be that COVID-19 continues to plague us long term.
Thankyou!
Thank you! Unfortunately you are correct or Covid will simply be one more “common” cold out there forever with a 1% mortality rate!!
One thing more, IF there is ANY chance the virus was developed in China as a potential biological weapon, which had been suggested a while back, and what we are going through is perhaps a “field test”, China must be thrilled. Who needs armies and bombs?
I actually think the early likelihood of a vaccine is because China was working on that simultaneously!! They HAD to share it after losing it from their lab!!