One year ago, Los Angeles County was well on its way to becoming the epicenter of the covid-19 pandemic. Here in the nation’s most populous county, we were averaging about 8,000 new coronavirus cases a day on our way to a peak of 16,000 on Jan. 1, 2021. Hospital capacity countywide was already severely strained, with 3,000 patients admitted with severe covid. Weary from working on the front line for nine months, we were eagerly awaiting the Food and Drug Administration to authorize the vaccine on an emergency basis.
Flash-forward to imm, and it’s a totally different situation. The seven-day average of hospitalizations due to covid hovers at around 750, considerably less than a year ago. After a seismic decline in non-covid patient visits for most of 2020 due to fear of the virus, our emergency room is back to its pre-pandemic volume of medical and surgical emergencies that have nothing to do with the coronavirus. This return to normalcy was entirely thanks to the vaccines, which were taken up enthusiastically here once authorized. Countywide, 78 percent of residents ages 5 and older and 84 percent of those 12 and older have received at least one dose of a vaccine.
Lately, discussion of the pandemic has centered on warnings about “waning immunity” and “declining antibodies,” particularly with the rise of the highly infectious omicron variant. But as we saw during the surge of the delta variant this summer, immunity is much more complex and diverse than antibodies. This biological reality undergirds our optimism that the vaccinated are still well protected from getting severe disease, and hospitals in highly vaccinated areas won’t again be overrun with covid patients.
It’s true that the neutralizing antibodies generated by the vaccines that prevent the virus from entering our cells wane over time, or can struggle against new variants like omicron. But the vaccines also generate something called cellular immunity, which is much more long lasting. Memory B cells triggered by the vaccines are able to produce new antibodies if they ever see the virus, even if it has mutated. A bout of covid is also known to generate these B cells, and B cells generated as a result of vaccination should be just as long-lasting, according to various studies. A 2008 Nature study found that survivors of the 1918 influenza pandemic were able to produce antibodies from memory B cells when their blood was exposed to the same influenza strain nine decades later.
The vaccines also trigger the production of T cells. While B cells serve as memory banks to produce antibodies when needed, T cells amplify the body’s response to a virus and help recruit cells to attack the pathogen directly. With vaccination or recovery from infection, we are likely to have covid-specific T cells that protect us against variants, including omicron. Despite omicron’s many mutations, binding sites on the virus known as epitopes can be recognized by T cells that then mark the virus for destruction. Because of this, we are unlikely to get a variant that will evade the robust response of our T cells.
While coming down with covid-19 can lead to the production of B cells and T cells, it is much safer to acquire this immunity via the two-shot mRNA vaccine, ideally followed by a booster shot. The reason, simply, is that covid-19 is a dangerous disease that can lead to death or long-term complications. In L.A. County in July, the hospitalization rate among the unvaccinated was 29 times that of fully vaccinated people during the delta variant surge. That rate has risen to 44 times in the past month. Severe illness in a fully vaccinated person remains rare even without the booster, with only those over 65 having any decline in protection against hospitalization, according to a New York state analysis.
The disease may have already ripped through some less-vaccinated parts of the country, leaving cellular immunity in its wake that will blunt the impact of an expected winter surge on hospitals. But it could still be a tough period for these regions, as we don’t yet know what proportion of the population might have had the disease, and there’s still a lot we don’t know about omicron. In less than one month, omicron has risen to become the cause of 73 percent of all new infections in the country. Even here in highly-vaccinated L.A. County, we have seen a tripling in daily reported cases. Even though early indications are that omicron may not cause more severe illness than delta, and despite the fact that we have better tools for treating covid and know so much more about the disease, both variants still pose a grave threat to the unvaccinated and could overwhelm hospitals in under-vaccinated areas.
For regions like ours that have embraced the vaccines, rising case counts shouldn’t result in the sort of emergency room crush we experienced a year ago. The cellular immune response among those who are fully vaccinated or have been previously infected with the coronavirus will persist, preventing many cases of severe illness and hospitalization. Cellular immunity is the most powerful defense we have against a pandemic. And as doctors on the front line seeing our emergency rooms and hospitals turn to other diseases, we can attest to its power.