With the remarkable news that at least two of the new COVID-19 vaccines are efficaciously suppressing symptoms and appear to be safe for a broad swathe of the adult population, two big questions about the vaccines themselves remain unanswered: “How well will they block transmission?” and “How long will the protection last?”
This latter property of a vaccine is called its durability. Some vaccines, such as those for Measles and Polio, remain almost completely protective for a lifetime. Others, such as for Tetanus, last about a decade. Vaccines for different strains of the flu are very short-lived—3 to 6 months, and even within that time frame the efficacy varies from strain to strain and year to year, and is typically 50% or less.
Due to how dangerous this virus is and how contagious it is, the only way to end this pandemic, save millions of lives, and enable the revival of the ever-elusive normalcy is to essentially vaccinate the whole world, 7.4 billion souls. This will be a staggering project, especially with vaccines that require two injections, as these do.
Needless to say, the less often these vaccinations must be repeated, the better. This is why durability is such an important question: durability of less than a year would require an endless epic global vaccination cycle, whereas durability of, say, five years would let the world devise a relatively efficient rhythm of virus control. We won’t know the answer to this question definitively until the vaccines and virus have been around together long enough to observe what happens, but there have been a few suggestive wisps of evidence.
The first wisp was not encouraging: this summer several people who had contracted and recovered from COVID-19 in the spring contracted the disease for a second time just a few months after recovering. This was sobering news, suggesting that natural immunity was short-lived.
However, in the ensuing months no large waves of reinfection have been detected, so perhaps this will remain a relatively rare phenomenon. In any case, it would not be surprising for natural immunity to be somewhat variable in the case of a disease like this one, where severity is also very variable, and the total number of cases is very large. Vaccine-based immunity is likely to be more consistently vigorous than the natural kind.
The next wisp, a more positive one, came in May, when scientists reported lower rates of COVID-19 infection and lower rates of severe symptoms in places where more people had received a relatively recent (10 years or so) MMR II vaccination. MMR II is the current vaccine for Measles, Mumps, and Rubella. Intrigued by this, another group of scientists did blood tests to determine whether levels of antibodies to Measles, Mumps or Rubella correlated with improved COVID-19 resistance. They reported their results in mid-November. In their small study (80 subjects), high concentrations of Mumps antibodies correlated strongly with COVID-19 resistance.
In an excellent story in South Seattle Emerald, my Post Alley colleague Kevin Schofield pulls together the details from these two scientific articles. Taken together, they suggest answers for two interesting questions: why are children so much less likely to have severe symptoms of COVID-19? Why are older people so much more likely to have severe symptoms? Children receive the MMR II vaccine at ages 1 and 5. Their resistance to COVID-19 seems to run from age 1-14. Perhaps MMR II is a factor.
MMR II was introduced in 1971. People born before that (all over 50) mostly didn’t receive that vaccine, so perhaps that absence is a factor. Kevin’s article does a good job of clearly summarizing the implications of this unexpected correlation between MMR II and COVID-19 resistance. I’ve included links below to Kevin’s story and the underlying articles.
To me, one intriguing thing to emerge from these studies so far has to do with durability, our topic for today. Durability depends on two things: first, the immune system must lock in a memory of the offending pathogen and hang onto it. Second, the pathogen must be unable to mutate around the vaccine-generated immunity, the way many pathogens can mutate around non-vaccine drug treatments (bacteria mutating to achieve resistance to antibiotics, for example).
If the Mumps vaccine is providing some protection against the SARS CoV-2 virus, that protection is coming in some cases many years after vaccination. This suggests that the immune system is capable of remembering something for a good long while that is effective against COVID-19. This is just a wisp, because the SARS CoV-2 virus which causes COVID-19 has only been infecting humans for about a year. Still, knowing that a vaccine not even developed to fight our current pandemic may create COVID-19 resistance years after injection suggests—in a whisper—that it might be possible to develop a COVID-19 vaccine that will also work for years.
We are also in early days with the new vaccines, meaning there are still ways in which the huge and borderline-shambolic vaccination programs intended for 2021 could be set back. Should that happen, it’s good to know that, possibly, there’s something of a backup plan available: Merck, the maker of MMR II, has vast production capacity and could increase the supply fast if the new vaccines stumble. Meanwhile, we need bigger studies of whether MMR II confers COVID-19 resistance. If it does, we need to know how it works, and we need to know whether it would be safe to inject a large older adult population with a vaccine primarily intended for 1- and 5-year-olds.
But enough about the Mumps. The most recent wisp came just before Thanksgiving, in an article about SARS CoV-2 mutation. The researchers were looking for evidence that the virus might be mutating in ways that would make it more transmissible. This is an important question, since the virus has just recently jumped to humans, and might be able to improve its adaptation to its new hosts. They concluded that, so far, no such mutation has occurred.
There have been plenty of small mutations—there always are with viruses—but they haven’t added up to the emergence of a strain with more advantageous contagiousness, one favored by natural selection. Given the abundant opportunities a global pandemic provides, this is also good news, of the wispy sort. It doesn’t mean that the virus can’t or won’t mutate under selection pressure from the vaccines, but it at least shows that it’s probably not the kind of virus that mutates at the drop of a hat when advantage presents itself. In other words, useful durability is still on the table for these vaccines.
Meanwhile, the greatest risk to us as the vaccines roll out is that enough of us won’t wear masks, stay home, stand back, and wash hands. Expecting our healthcare system to vaccinate 330 million people in the middle of an uncontrolled pandemic is like asking a fire department to put out a five-alarm blaze while their fire hoses are on fire. But I digress.
Links:
Kevin Schofield’s story about MMR II:
MMR II vaccine history correlates with COVID-19 resistance:
https://www.researchgate.net/publication/341354165
Mumps antibodies in the blood correlate with COVID-19 resistance:
https://mbio.asm.org/content/11/6/e02628-20
The lack of evidence for increased transmissibility from recurrent mutations:
