Viruses mutate all the time, including the novel coronavirus that’s caused the global Covid-19 pandemic. Most of the changes have no apparent effect. But recent variants that have emerged in the U.K., South Africa and Brazil are causing particular concern. They don’t appear to be any more virulent, but studies suggest they are more contagious than other strains. More people getting infected could lead to a surge in hospitalizations -- as has happened in England and elsewhere -- and potentially more deaths. Authorities have imposed new travel curbs and continue to urge people to take precautions in public, like wearing masks. Drugmakers say their vaccines should still be effective, while research is ongoing.

1. How serious is this?

The variant that emerged in southeast England in September, dubbed the B.1.1.7 lineage, contributed to a spike in cases in December that sent the U.K. back into lockdown. It also prompted many places, including the U.S., to halt air and train travel from the U.K. or impose new restrictions. Other countries have followed with tighter lockdowns, particularly in Europe. Health officials warned the strain could become dominant in the U.S. as soon as March. In southern Africa, hospitals are facing pressure from a resurgence driven by another variant there, 501Y.V2. Brazilian researchers are warning that a so-called P.1 variant spotted in Manaus, Amazonas state, in December could be aggravating an outbreak there. Four Japanese travelers returning from Amazonas in early January were found to have the virus during routine screening at Tokyo’s Haneda airport. The U.K. imposed its own ban on travelers from South America.

2. What’s causing this?

Preliminary analyses suggest these new variants are more likely to spread among people than other circulating SARS-CoV-2 strains. South Africa’s genomic scientists have found the new strain there is about 50% more transmissible than earlier versions. The variant in the U.K. has been found to be 56% to 70% more transmissible. It has acquired 17 mutations compared to its most recent ancestor -- a faster rate of change than scientists typically observe. Researchers have found no evidence that it causes a more severe illness. A report by Imperial College London researchers released on Dec. 31 found “a small but statistically significant” indication that the B.1.1.7 strain affects younger people -- those under 20 -- more than others do, though the reason could be circumstantial. An analysis of 641 Covid-19 cases in the U.K. found those with the variant had 10-to-100 times higher concentrations of the coronavirus in their noses compared with infections caused by “regular” SARS-CoV-2, which may explain the higher transmissibility.

3. How quickly have they spread?

Rapidly, becoming the dominant strains in multiple countries, aided by year-end holidays that are traditionally associated with increased family and social mixing. By early January, cases caused by the B.1.1.7 variant had been identified in some 50 countries or territories, including the U.S., Australia, Canada, Germany, Italy, Japan, Lebanon, the Netherlands, Singapore and South Korea. Similarly, the 501Y.V2 variant that was first detected in Nelson Mandela Bay, South Africa, in early October has led to a steep rise in cases across nine southern African countries as well as the Seychelles and Mauritius. In mid-January a case was reported in Denmark.

4. How much are the variants increasing transmission?

Factors such as people congregating indoors more in colder weather may also contribute to spread. But the new variants appear to have some advantage over other versions that has enabled them to quickly predominate. The U.K.’s New and Emerging Respiratory Virus Threats Advisory Group noted in December that the B.1.1.7 lineage may result in an increase in the basic reproduction number, or R0 (the average number of new infections estimated to stem from a single case) in the range of 0.39 to 0.93 -- a “substantial increase in transmissibility compared to other variants.” Infection rates in areas where the strain has been circulating have increased faster than expected, Public Health England said Dec. 20. It reported in January that patients infected with the variant were more likely to infect their contacts than if they had a “regular” strain.

5. How many mutations are there?

Many thousands of mutations and distinct lineages have arisen in the SARS-CoV-2 genome since the virus emerged in late 2019. A variant with a so-called D614G mutation emerged in early 2020. By June, it had replaced the initial strain identified in China to become the dominant form of the virus circulating globally. Months later, a novel variant linked to farmed mink was identified in a dozen patients in North Jutland, Denmark, but doesn’t appear to have spread widely. As mutations continue to arise, they will lead to more new variants.

6. Are some mutations more important?

Yes. Scientists pay most attention to mutations in the gene that encodes the SARS-CoV-2 spike protein, which plays a key role in viral entry into cells. Targeted by vaccines, this protein influences immunity and vaccine efficacy. The B.1.1.7, 501Y.V2, and P.1 variants all carry multiple mutations affecting the spike protein. That raises questions about whether recovered and vaccinated patients will be able to fight off the new variants with an antibody response. Research by Public Health England in January found that those previously infected with the “regular” coronavirus are likely to mount an effective antibody response against the B.1.1.7 variant. But that same month the first known instance of a person being reinfected with the P.1 variant was reported in Brazil.

7. So will vaccines be effective?

Drugmakers including Pfizer Inc., BioNTech SE, AstraZeneca Plc and CureVac NV have said they don’t believe their vaccines’ efficacy will be affected, and scientists at the U.S. National Institute of Health are studying the issue. A small study at the University of Texas Medical Division found the Pfizer-BioNTech vaccine would likely still be effective against a key mutation in the U.K. and South African variants, but they didn’t look at the full set of mutations involving the spike protein in the rapidly spreading strains. Over time, as more mutations occur, vaccines may need to be altered. This happens annually with seasonal flu, which evolves quickly. Unlike flu, coronaviruses have a genetic self-correcting mechanism that minimizes mutations. Covid-19 shots that have proved effective in trials can be easily tweaked if necessary, vaccine makers said.

8. Are there any other implications?

The U.S. Centers for Disease Control and Prevention has said new strains might undermine the performance of some PCR-based diagnostic tests. The impact, though, isn’t likely to be significant, according to the World Health Organization.

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