Question: If having antibodies doesn’t confer protection, then would a vaccine even work?
Answer: Great question! First, let me provide some more information on antibodies and protection, then a direct answer to your question.
Yesterday, WHO came out with some guidance on “immunity passports,” stating that “As of 24 April 2020, no study has evaluated whether the presence of antibodies to SARS-CoV-2 confers immunity to subsequent infection by this virus in humans.” Some media outlets ran with this, stating “WHO warns you may catch coronavirus more than once.” This take is, unfortunately, a bit of sensationalism (in my opinion). As the old saying goes, absence of evidence is not evidence of absence. In the case of antibodies and ongoing protection, with just 4 months into this new virus and disease, we just don’t know. And we wouldn’t want to base huge policy prescriptions — like immunity passports — on a hunch (as discussed in Q&A of 4/13 and 4/15). To my knowledge, most health experts believe, based on historic precedent, that antibodies would offer some degree of protection. Earlier this month, Dr. Fauci spoke with JAMA’s editor, stating that “It’s a reasonable assumption that this virus is not changing very much. If we get infected now and it comes back next February or March we think this person is going to be protected.” But, with lots of folks’ bodies/immune systems reacting in what seems to be different ways to the virus — with an estimated 80% of cases being mild, some people being asymptomatic, and still others having a variety of serious symptoms and outcomes, it’s even harder to make an educated guess. Moreover, having antibodies is more than a yes/no dichotomy; it’s a continuum — and the more antibodies you have, the more likely you are to be better protected. Just what level of antibodies required to protect against reinfection, however, is unknown, and just how long such immunity would last is also unknown. For other types of coronaviruses, the immunity offered against reinfection wanes after a year or two (as discussed in Q&A of 3/19).
So, what does this all mean for vaccines? The National Academies rapid expert consultation of April 8th has the best quick read on the subject that I’ve come across:
“The duration of antibody response and acquired immunity to reinfection will be critical to understanding 1) how effective vaccination is likely to be; 2) how durable immunity is; 3) whether it is possible to achieve herd immunity against COVID-19; 4) how safe it is for people who are positive in a serology test to return to work. One key uncertainty arises from the fact that we are early in the outbreak and survivors from the first weeks of infection in China are, at most, only three months since recovery….”
And copied herein is the experts’ list of gaps in knowledge. The knowledge that we’ll continue to gather will influence vaccine design and our expectations of vaccine efficacy, including how frequently vaccine boosters may need to be given.
National Academies Expert Consultation:
