Unanswered questions remain
“How long this immunity lasts, we don’t know,” Dr. King said. He predicted that antibody protection could last a year to a year and a half. The duration of protection could vary. “We know some people lose their antibodies pretty quickly, and other people don’t,” he said.
Dr. Slifka said the suggestion of “a substantially reduced risk for at least 6 months ... is great news, and the timing couldn’t be better, because we’re rolling out the vaccines.”
Not all antibody responses are alike. For example, data indicate that antibody levels following immunization with the Pfizer/BioNTech or Moderna vaccines are higher on average than those of people who’ve had a natural infection, Dr. King said. He added that initial data on the AstraZeneca COVID-19 vaccine in development showed lower antibody levels compared with natural immunity.
The Centers for Disease Control and Prevention recommends immunization for those with a history of infection. “People who have gotten sick with COVID-19 may still benefit from getting vaccinated,” the CDC notes on its Facts About COVID-19 Vaccines website. “Due to the severe health risks associated with COVID-19 and the fact that re-infection with COVID-19 is possible, people may be advised to get a COVID-19 vaccine even if they have been sick with COVID-19 before,” the CDC stated.
The agency also notes that people appear to become susceptible to reinfection approximately 90 days after onset of infection. However, the new evidence from the UK study that persons have up to 6 months of immune protection might lead to a modification of recommendations, especially at a time when vaccine supplies are limited, Dr. Slifka said.
Another unanswered question is why the two study participants with antibodies subsequently tested positive for reinfection. “There are a lot of things that could have made these people more susceptible,” Dr. King said. For example, they could have been heavily exposed to SARS-CoV-2 or been immunocompromised for another reason.
Furthermore, the immune response involves more than antibody levels, Dr. King noted. Research in rhesus monkeys suggests that T cells play a role, but not as prominent a part as antibodies. “What I think is protecting us from infection is primarily the antibodies, although the T cells are probably important. Once you get infected, the T cells are probably playing a more important role in terms of whether you get very sick or not,” he said.
Multiplication + addition = more protected?
The 90% natural immunity protection in the study approaches the 95% efficacy associated with the Pfizer and Moderna vaccines, Dr. Slifka noted. Even without immunization, this could mean a portion of the U.S. population is already protected against future infection.
Furthermore, the CDC estimates that there are about 7.7 cases of COVID-19 for every case reported.
As of Sept. 30, the CDC reported that there were 6,891,764 confirmed cases. The agency estimated that overall, approximately 53 million people in the United States have been infected. More recent numbers from Johns Hopkins University’s Coronavirus Resource Center indicate that there were 18.2 million cases in the United States as of Dec. 22. If that tally is multiplied by 7.7, the total number protected could approach 140 million, Dr. Slifka said.
“That could really be a boost in terms of knocking this pandemic down in the next couple of months,” Dr. Slifka said.
“Now, if we were to modify the current recommendations and briefly defer vaccination of people with confirmed cases of COVID-19 until later on, we could start reaching herd immunity pretty quickly,” he added.