The good news on COVID-19: Immunity seems to last and vaccines are on track

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There are over 300,000 viruses that infect mammals, but there are only seven coronaviruses that infect humans. Four of these, known by the less-than-alternative labels 229E, NL63, OC43, and HKU1 produce generally mild illnesses and are responsible for about 15% of what people refer to as the “common cold.” Exposure to these viruses generates a mild and rapidly falling immune response, meaning that people can be infected again by the same coronavirus in a matter of a few months.

Of the remaining human coronaviruses, two are SARS-CoV and MERS-COV, which generate extremely serious illness with a high rate of fatalities. And then there is SARS-CoV-2, the virus behind the disease COVID-19. From the beginning, there have been worries that this virus might combine the worst of other coronaviruses: highly infectious, deadly, and not generating a lasting immune response. That nightmare scenario has had researchers, and a lot of nonresearchers, holding their breath for months. Well … breathe. COVID-19 is a rat bastard of a disease, but the latest indications are that it’s not going to turn into an endlessly spinning cycle of disaster. We really can put this thing behind us.

The fact that some coronaviruses do not create a lasting immune response has been a shadow over the COVID-19 pandemic from the beginning, and there have certainly been a series of reports that have made that shadow seem darker.

Early on, officials in Hubei Province indicated that as much as 15% of patients were testing positive for COVID-19 a second time after having a negative result. These numbers were seriously alarming, especially as this 15% rate of secondary infection happened in a very brief period. However, it’s almost certain that these results were more related to testing errors in China’s early antibody-based testing. No other country has reproduced these results, or anything like them.

However, as researchers began looking into the immune response generated by COVID-19, it became clear that in many cases patients with the mild or asymptomatic cases had relatively low levels of antibodies when compared with patients—especially older patients—who had gone through more severe cases. And follow-up studies indicated that the level of antibodies for all cases dropped off 15%-40% over a period of just two or three months, meaning that some of those mild cases dropped to the point where they no longer tested positive. Antibodies are far from the only measure of immune response, but this did increase the worries that immunity to COVID-19 might be weak and fleeting.

However, a paper that reached preprint last week provides some reassuring information right in the title: “SARS-CoV-2 infection induces robust, neutralizing antibody responses that are stable for at least three months.” This study, based on a large database of nearly 20,000 patients treated at New York City’s Mount Sinai Hospital, showed that the “vast majority” or patients with mild or moderate COVID-19 still had strong antibody responses to the viral spike protein from SARS-CoV-2 three months later. The expectation of the authors is that at least 90% of all patients are immune to reinfection for at least three months.

This is absolutely not the last word on this subject. For one thing, this paper is still undergoing peer review. For another, the number of anecdotal cases of someone testing positive, then negative, then positive again indicates that, at the very least, some people experience a resurgence of the virus, if not a true second infection, within a short period. It still seems entirely possible that people who tested positive on a PCR swab test but had a very mild immune response might be susceptible to a second infection within a short period.

All of this makes it more important that any potential COVID-19 vaccine produce an immune response robust enough to avoid any concerns about rapid drop off. And there’s good news on that front as well. Phase 2 results of the Oxford vaccine have been published in The Lancet, and they’re as good—and maybe even better—than anyone had hoped. In earlier animal testing, the Oxford vaccine had produced a less robust antibody response than either the Moderna or Pfizer vaccines, and actually a lower level than found by patients experiencing a moderate case of COVID-19. However, the actual vaccine in actual patients worked better.

As with the Moderna vaccine, the Oxford vaccine involves two shots given 28 days apart. And just as with the Moderna results released earlier this month, a number of the Oxford patients experienced relatively mild side effects (fever, chills, muscle aches, headaches) similar to the experience of patients receiving a flu vaccine. Unlike the Moderna trial where one person developed a serious fever, there were no strong side effects. After the first shot, 91% of patients had a measurable neutralizing antibody response against SARS-CoV-2. After a second shot, that number was 100%. The rate of the response was in the mid-range of levels seen in convalescent plasma—which is lower than the response seen in the Moderna phase 1 numbers, but there’s no indication that the Oxford numbers aren’t sufficient.

Full development of a response in all patients took until about 14 days following the booster shot—so even when the vaccine is available, everyone may face something of a maddening six weeks between visiting the doctor and feeling fairly safe from COVID-19. However, some people in the U.K. may get to start that countdown surprisingly soon as the Phase 3 studies could be done in September if everything goes well. It’s entirely possible that some healthcare workers could be getting their initial injection around Halloween.

Overall, the results from vaccine tests have been good, and the latest studies on lasting immunity to COVID-19 look good. Everything indicates that this nightmare does have an end.

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