News about emerging coronavirus variants can sound scary to a public not accustomed to genomic jargon. But viruses undergo mutations frequently, both within infected people and as they travel from one person to another. That’s why it’s important to remember this (modified) adage: All variants are innocent until proven guilty.
The coronavirus responsible for the pandemic, SARS-CoV-2, has nearly 30,000 bases, or nucleotides. As the virus evolves and spreads from host to host, some of these bases change. If just 20 bases changed, that would yield more than a trillion possible variants different from the strain responsible for the first outbreak. Of the 136 million confirmed Covid-19 cases in the world to date, one million individuals have had their virus sequenced. And of those one million sequences, scientists have been concerned about only a handful of variants, because they are more infectious, cause more severe illness or partly evade our immune response or all of the above.
In other words: Hundreds of thousands of sequences have not been associated with substantive changes in the virus’s behavior. These changes can help scientists track how and where the virus is spreading, but they have no medical significance.
Five variants have now been proved guilty, as shown by the Centers for Disease Control and Prevention’s designation “variants of concern.” They are B.1.1.7 (first identified in Britain), B.1.351 (first found in South Africa), P.1 (identified in Brazil) and two more recent variants found in California and New York. Each has fewer than two dozen notable mutations, many of which are in the virus’s spike protein, which binds to our cells and is the vaccines’ principal target. Some mutations enhance the virus’s ability to bind to the cells lining our upper airway, while others interfere with our bodies’ capacity to mount a full immune response.
Critically, the number of mutations does not necessarily correlate with any change in the virus’s infectiousness. For example, a variant in Angola was recently found to have the most mutations to date, but there isn’t any clear evidence that it causes more disease. It takes considerable work — studies in the lab as well as in large numbers of people — to ascertain whether a variant might cause an increase in cases, hospitalizations, fatalities and reinfections.
The vaccines being administered in the United States were developed before some variants emerged. But so far, they appear to be effective in fighting those viruses. The Moderna and Pfizer vaccines, which use a technology called mRNA, have been shown in laboratory studies to be effective against each of the major variants. Even when the variants make the vaccines less effective, the mRNA coronavirus vaccines in use right now are so good that a reduction would not likely affect the efficacy rate in a meaningful way.
The limited amount of evidence available for the Johnson & Johnson, AstraZeneca and Novavax vaccines suggests that they remain mostly effective at tackling the variants. So far, the B.1.351 variant appears to be the most able to evade the vaccines, but studies indicate the shots still succeed at preventing significant illness.
In the United States, B.1.1.7 has become the dominant variant. Think of B.1.1.7 as a superspreader version of the virus, able to outrun variants that can’t transmit as efficiently. We know from Britain, where this variant has been responsible for nearly 100 percent of infections, that vaccinations have been highly effective in reducing cases, hospitalizations and deaths. Reports from Israel, which has vaccinated its population more quickly than any other country, have shown that the mRNA vaccines’ efficacy was not diminished by the three most common variants of concern.
The United States is seeing the beginning of a fourth wave of Covid-19, most dramatically in Michigan, where in the past two weeks the number of new cases has risen 60 percent and deaths and hospitalizations have more than doubled. Vaccines weren’t available in previous surges, but now with an influx of vaccines, we can stop a spike in cases as soon as it appears. Unfortunately, the United States is rigidly committed to allocating vaccines based only on population, rather than using a targeted approach to tamp down hot spots like Michigan. This approach is contrary to what has been proved to work in Israel, Britain and other countries.
The major variants pose a challenge, but the extraordinary efficacy of our vaccines will ultimately override them. That’s in part because vaccines induce a far broader and powerful immune response than humans do in response to coronavirus infections. But it’s critical that we contain the virus so it’s unable to evolve further and theoretically dodge our vaccines.
Vaccines are a vital tool, but masks and distancing work well against the variants. Combining these mitigation strategies with vaccination is the fastest way for us to emerge from the pandemic. The science of virus variants and evidence from our vaccine armamentarium should instill confidence that we’re moving toward the exit ramp.
Eric J. Topol (@erictopol) is a professor of molecular medicine at Scripps Research and served on the advisory board of the Covid Tracking Project.
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